Patent Publication Number: US-9897523-B2

Title: Contact mechanic tests using stylus alignment to probe material properties

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application No. 62/128,753 filed Mar. 5, 2015, U.S. Provisional Patent Application No. 62/237,950 filed Oct. 6, 2015, and U.S. Provisional Patent Application No. 62/270,416 filed Dec. 21, 2015, the disclosures of which are incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the use of contact mechanics to gain data and information related to material state and properties, and more specifically to the sampling of material surface characteristics, including mechanical behavior, without requiring the use of conventional cutting or machining tools to remove a large sample from an existing structure, component or product. 
     BACKGROUND ART 
     Engineers and other decision-making agents utilize data about the materials of fabrication of load bearing structures to determine their durability, reliability and the overall safety. The data can be from a number of sources including the original manufacturing specifications, from manufacturing quality control, or from measurements done after the fact as part of condition assessment. Non-destructive testing (NDT) methods are appealing because they allow for estimating the characteristics and properties of assemblies and structures without damaging or jeopardizing the function of the structure during testing. 
     Non-destructive testing during condition assessment on existing structures in the field is very important to safety and the protection of the environment. We have a large inventory of existing infrastructures that may have changed from the time they were originally manufactured as well as existing infrastructures that would not meet the current standards of design and fabrication. One goal with condition assessment is to minimize the risk of a catastrophic event such as the break of a large oil or gas pipeline, the collapse of a bridge or the failure of a large pressure vessel. These events still occur too frequently in our society. 
     Non-destructive testing can be used to evaluate, among others, the existence and size of cracks, changes in material thickness for corrosion, and the properties of the materials. Properties of the materials that can be of interest include the chemistry, mechanical properties and the cracking resistance under the service environment and/or the cyclic loads. 
     Current industrial non-destructive techniques for mechanical properties can be limited in scope to measuring the hardness of a material by indentation, which provides an index of a material&#39;s resistance to penetration by a hard indentor or stylus. Although indentation testing is widely used, the traditional equipment provides a hardness value which is not a reliable measure of mechanical properties such as yield strength or ultimate strength, and provides no measure of ductility. A recent variation of the indentation hardness test uses a series of spherical indentations of progressively increasing depth at the same material location to provide an estimate of the stress-strain curve of the material. This technique requires generating multiple indents in each region of the structure where an estimate of the material properties is desired. Therefore, these series of indents have limitations with respect to the study of microstructural gradients, such as changes in properties through welds and surface modifications. This apparatus and method are detailed in U.S. Pat. No. 6,945,097 B2 dated 20 Sep. 2005. Another variation is instrumented indentation, whereby the reaction force on the stylus and its relative displacement is monitored during a loading and unloading cycle. The load-displacement information is then used to predict material hardness and elastic stiffness as described in Oliver and Pharr&#39;s 1992 paper, “An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation techniques.” More recently, Dao et al. utilized the load-displacement information along with numerical models to develop predictive algorithms for determining the complete stress-strain curve. 
     It is known in the prior art to use a hard indentor or stylus to deform materials by applying a vertical force and displacement and inducing a lateral movement of the indentor or stylus. These tests are often called scratch, or contact mechanics experiments. They introduce material and geometrical changes to the substrate surface. Contact mechanics tests have been used for material characterization throughout history, including in 1812 with the publishing and later broad adoption of the Mohs scale of mineral hardness. Over the past decades, advances in instrumentation to perform contact mechanic experiments have helped to elevate the amount of information that can be obtained through contact mechanics experiments. A number of test apparatus and methods have been developed and disclosed. However, the apparatus and techniques known to the inventors assume that the substrate can be brought at a desired angle with respect to the stylus. 
     Currently, contact mechanics tests are used to measure the strength of thin-films and coatings. This test is done by using a hard stylus to engage with the material while moving the stylus along the material&#39;s surface and controlling the load being applied to the stylus until failure occurs. This testing method is described in U.S. patent application Ser. No. 10/362,605, and is limited to select applications where materials utilize thin-films or coatings. This restriction makes the technology unsuited for assessing mechanical properties of common engineering materials. In addition to coating strength, recent academic research by A. T. Akono et al. has used contact mechanics tests in an attempt to correlate with the fracture toughness of materials. The implementation assumes that the crack forms at the apex of the stylus in-front of the direction of sliding. Contact mechanics tests have also been utilized to predict the yield strength and ductility of metals through the use of numerical modeling and dimensional analysis. All of these contact mechanics methods utilize existing laboratory testing devices and systems, but the underlying test apparatus is either too complex or not sufficiently accurate for broad commercial use. As a result, existing testing systems provide only partial solutions for evaluating mechanical properties. 
     Based on the above, contact mechanics experiments are not performed in the field or in industrial facilities as much as they could be if the capabilities were improved. Field testing solutions have been developed using indentation techniques. Examples include the King Portable Brinell Tester, Telebrinell Tester, Shear Pin Brinell Tester, Leeb (or rebound) Tester, and Automated Ball Indentation (ABI) Tester. These field devices use various methods of aligning the system with the structure being tested. Each method, however, requires the use of contact points that remain stationary. As a result, the devices must be connected and disconnected for each individual test location, or alignment of the devices is not maintained. Furthermore, these indentation testers provide limited information about the ductility of the material, especially within the heat affected zone of welded joints. Indentation testing also typically provides limited information with respect to the cracking resistance and toughness of the material under service conditions. The ductility of a material is an indication of how it will stretch or deform permanently before it breaks. The alternative solution for evaluating existing structures in the field is material removal for laboratory testing, which requires repair and limits the number of locations that can be tested without jeopardizing the integrity of the structure. 
     In some instances, the surface properties of the material that is measured through contact mechanics may not be representative of the bulk behavior. This is because gradients in properties may exist due to prior fabrication and manufacturing processes. These processes include heat treatments, cold forming, hot rolling, shot-peening, and others. There are currently no existing methods to systematically account for these gradients in mechanical properties, and therefore contact mechanics tests are only applicable for the small volume of material that is directly probed. 
     SUMMARY OF THE EMBODIMENTS 
     In one embodiment of the invention, an apparatus for performing a contact mechanics test on a substrate, the apparatus comprising (i) a stylus having a principal axis and shaped to deform the substrate at a stylus contact location, (ii) a core, in which the stylus is hosted, configured to engage the stylus against the substrate, (iii) a stylus engagement mechanism, coupled to the core or the stylus, configured to induce a contact load or a penetration depth to the stylus, (iv) a core engagement mechanism, coupled to the core, configured to maintain contact of the core and to move the core along the substrate surface, (v) a frame, in which the core engagement mechanism is hosted, configured to be fixed with respect to the apparatus or to be moved together with the core engagement mechanism as an assembly, (vi) a frame engagement mechanism configured to engage the frame with the substrate surface, and (vii) a substrate monitoring device configured to measure characteristics of substrate contact response, collect material machined from the substrate, or both. In this embodiment, the core, the core engagement mechanism or the frame engagement mechanism includes an alignment mechanism configured to provide a desired local angular orientation of the principal axis of the stylus relative to the substrate surface at the stylus contact location. In another embodiment of the invention, a method for performing a contact mechanics test on a substrate surface using one or more styluses, each stylus having a principal axis and shaped to deform the substrate surface, the method comprising (i) maintaining the principal axis of the stylus at a desired local angular orientation with respect to the substrate surface, (ii) causing the stylus to engage and deform the substrate surface, (iii) re-aligning the stylus as or after the stylus engages the substrate surface, and (iv) measuring a substrate contact response. 
     In another embodiment of the invention, a method for determining the distribution of material properties at any location of a structural component through a local measurement obtained at a known position. This is achieved by (i) obtaining a local measurement with experimental testing, (ii) developing a computational model of the changes in the initial material properties within a structural component induced by one or more manufacturing processes, (iii) developing an algorithm through multiple computational models considering various initial stress-strain curves to correlate fabricated material condition gradients with initial uniform material properties, and (iv) verification and refinement of the algorithm based on material properties directly measured through contact mechanics from exemplar materials in the field or laboratory. 
     In some embodiments of the apparatus, one or more coupled components are contiguous. The apparatus may further include a mount, configured to attach to the substrate surface, having a magnetic device or attachment mechanism that allows the apparatus to be portable. The apparatus may be coupled to the substrate surface in order to perform contact mechanics with a frictional sliding test on the substrate surface. The apparatus may also be coupled to the substrate surface in order to perform contact mechanics with a series of indentation tests on the substrate surface. The core may further comprise an alignment mechanism that includes two or more floats configured to contact the substrate surface away from the stylus contact location in order to perform contact referencing without significantly damaging an area of the substrate being tested. The frame engagement mechanism may include an alignment mechanism utilizing a pre-set track in order to perform path referencing. The alignment mechanism may be configured to adjust for position and contour of the substrate surface through control of the local angular orientation of the stylus with respect to the substrate surface to perform scanning referencing. The stylus engagement mechanism may measure force or displacement in an orientation normal or in plane with the substrate surface. The core may host two or more styluses in parallel or in sequence, wherein the styluses have similar or dissimilar geometries, to perform two or more contact mechanics tests in parallel or in series. The core may host one or more wedge-shaped styluses which are used to generate a substrate contact response, including micromodifications on or beneath the sample surface. Two or more cores may be provided along with corresponding core engagement mechanisms for performing the contact mechanics test simultaneously or sequentially in different substrate surface areas or orientations. The core engagement mechanism may include at least one torsional spring. 
     In some embodiments, the method of utilizing stylus alignment may further include the preparation of the substrate surface prior to engaging the substrate surface with the stylus. The method may further include rehabilitating the substrate surface subsequent to measuring the substrate contact response. The method may utilize a contact mechanic test in a frictional sliding test mode. The method may utilize contact mechanics in a series of indentation tests mode. The method may re-align the stylus by contact referencing. The method may re-align the stylus by path referencing. The method may re-align the stylus by scanning referencing. The method of claim  15 , further comprising controlling surface friction through the condition of the contact surfaces or lubrication. The method may further include the determination of the surface-to-surface friction coefficient experimentally through repeated frictional sliding tests on the same location of the substrate surface. The method may further include measuring the thickness of the substrate before and after preparing the substrate surface and/or before or after the contact mechanics test. The method may further include a contact mechanics test that is performed in more than one direction and orientation with respect to the sample surface. The method may further include the implementation of two or more contact mechanics tests performed in series or parallel while utilizing different stylus geometries to induce different effective strains within the substrate. The method may further include measuring the substrate contact response at multiple times to quantify rate-dependent and time-dependent strain release through viscoelastic and viscoplastic relaxation. The method may further include the use of the characteristics of the substrate contact response to predict mechanical properties using predictive equations derived from finite element analysis or by correlation of experimental data. 
     In some embodiments, the method determining the distribution of material properties at any location of a structural component through a local measurement obtained at a known position further may use local surface measurement taken on the surface of a structural component using a contact mechanics test. The method may further include the use of local measurement is of the material yield strength, ultimate tensile strength, strain hardening exponent, hardness, or fracture toughness. The method may further include a validation database which is used to develop and iterate the predictive algorithms. The method may further comprise the prediction of an effective property from the material condition gradient to obtain a single representative value for comparison with standardized tests that probe a larger sample volume. The method may further include the prediction of an effective property through further computational modeling, analytical equations according to homogenization theory, or validation database. The method may further include the consideration of an effective property that is the material yield strength, ultimate tensile strength and/or strain hardening exponent that is measured experimentally through laboratory tensile testing or contact mechanics. The method may further include an effective property which is the material fracture toughness or material properties from Charpy V-Notch testing. 
     DEFINITIONS 
     Definitions. As used in this description and the accompanying claims, the following terms shall have the meanings indicated, unless the context otherwise requires: 
     A “substrate” is the material being probed for mechanical properties through a contact mechanics test. 
     To “deform” or producing “deformation” includes making a permanent or time-dependent change in the shape of the substrate, including by removal of material from the substrate. In some instances, the deformation will also include micromodifications. 
     A “stylus” is an element engaging the substrate. The stylus geometry may be conical, spherical, 3-sided pyramid, 4-sided pyramid, wedge-shaped, or a combination thereof. 
     A “contact mechanics test” is the use of one or more styluses to create localized deformation and probe the mechanical response of a substrate while the rest of the structure remains unchanged. Specific implementations include a series of indentation tests, whereby for each indentation a hard stylus deforms the surface of a softer substrate by moving with its principal axis at a target angle approximately perpendicular to the substrate surface. Another implementation is a “frictional sliding test,” whereby a hard stylus deforms the surface of a softer substrate while moving the stylus in a direction tangential to the local substrate surface. A contact mechanics test may be performed in a “machining” mode, where the stylus geometry, frictional contact conditions, and stylus travel velocity are selected to ensure that a ribbon or chip of material is removed from the sample surface. A contact mechanics test may also be performed in a “ploughing” mode, where the stylus geometry, frictional contact conditions, and stylus travel velocity are selected to ensure a ductile material response without any chip formation. Finally, the deformation can be in an opening mode where the material is flowing on each side of a wedge-shape. 
     An “irregular” surface is a substrate surface having local deviations from a planar orientation. 
     A “principal axis” of a stylus is defined as (i) the axis of revolution of the leading portion of the stylus, or as (ii) the axis intersecting the center of mass of the stylus with the leading portion of the stylus penetrating the furthest into the substrate. 
     A “local angular orientation” is the relative angle formed between a principal axis of the stylus and the direction tangent to the substrate surface at the position of engagement with the stylus. 
     A “frame” is a stiff element connecting the various apparatus devices, components, and subassemblies to a frame engagement mechanism. 
     A “frame engagement mechanism” is a combination of supports and mounts which engage the frame with the substrate surface. 
     A “mount” is a device or subassembly which operate and may consist of any combination of magnets, cables, belts, rails, wheels, rollers, fasteners, or adhesives. 
     A “multiaxial attachment” is a connecting member that may limit, transfer, or alter one or more degrees of relative motion between two or more devices and/or links connecting devices. 
     A “translational attachment” is a multiaxial attachment which limits the relative translation along up to two local axes and the rotation about at least two local axes. 
     A “rotational attachment” is a multiaxial attachment which limits the relative rotation about up to two local axes and the translation about at least three local axes. 
     A “float” is an element contacting the substrate outside of the area being engaged by the stylus for the purpose of maintaining a local angular orientation of the stylus. 
     A “rocking float subassembly” is an assembly of devices that allows for the independent relative motion between two or more floats, and may be configured to include,
     (i) “independent floats” which are floats that move with respect to floats mounted directly to the core,   (ii) a rotational attachment,   (iii) an “on-core attachment” which is a subassembly attachment location on the core that the rocking float subassembly can be mounted to via a rotational attachment,   (iv) an “off-core component” which is a supporting member that may be attached to the core independently of the rocking float subassembly,   (v) an “off-core attachment” which is a subassembly attachment location on an off-core component that the rocking float subassembly can be mounted to via a rotational attachment,   (vi) a “float subassembly stabilizer” which is any number of springs and/or limit stops that controls the motion of the rocking float subassembly,   (vii) a “pivot attachment” which is a subassembly attachment location where the rocking float subassembly directly contacts the core to provide independent motion while being mounted or stabilized by a float subassembly stabilizer.   

     A “mode of displacement” is a combination of linear and/or rotational displacements about relative axes which describes the allowable motion of an attachment and connected devices and/or linkages. 
     An “alignment mechanism” is an apparatus to establish the position and/or local angular orientation of the principal axis of the stylus relative to an irregular substrate surface which may be accomplished through
     (i) “path referencing,” which is when the alignment mechanism is defined by a pre-set path which guides the mode of displacement of the core,   (ii) “contact referencing,” which is when the alignment mechanism utilizes two or more floats which contact the substrate surface outside of the area engaged by the stylus in order to orient the stylus relative to the substrate surface, or   (iii) “scanning referencing,” which is when the alignment mechanism probes the substrate surface topography, either before or during a contact mechanics test, and makes continuous adjustments of the local angular orientation of the principal axis of the stylus to adequately engage with the substrate.   

     A “stylus engagement mechanism” is a device that transfers forces to the stylus to penetrate the substrate surface during a contact mechanics test by either (i) applying force through the stylus or (ii) developing a reaction force locally normal to the substrate surface by setting an engagement depth of the stylus relative to the substrate surface. The stylus engagement mechanism may be directly coupled to the stylus or integral to the core. The stylus engagement mechanism may also be configured to measure a normal force and/or tangential force resulting from the engagement between the stylus and the substrate. 
     A “load control” test is when the stylus engagement mechanism is set to apply a known and nearly constant load (through the stylus) to the substrate. 
     A “displacement control” test is when the stylus engagement mechanism is set to maintain a constant the stylus relative to the surface of the substrate which is set by floats. 
     A “constant demand” condition is setting the stylus engagement mechanism in load control or displacement control. 
     A “core” is an element that transfers the action from external devices to the stylus. The stylus and the stylus engagement mechanism can be contiguous with the core so that the core and the stylus are formed from the same material (such as zirconia), or can be separate components. These external devices may include the alignment mechanism and core engagement mechanism. 
     A “core engagement mechanism” is a device configured to control the path of the core during the test. The path can be translational, rotational, or a combination thereof. 
     A “normal force actuator” is a device that, when a contact referencing alignment mechanism is used, applies a sufficient force to maintain the contact between the core and the substrate surface. 
     A “yoke” is a connecting member that may transfer the translational and rotational forces and displacements from the core engagement mechanism to the core without impeding the functionality of the normal force actuator(s). 
     A “transfer module” is an assembly that transfers the desired displacements and forces from one or more actuators to an alternate point of application, and is configured to couple the frame, core engagement, and core, or any combination thereof. For a specific application, one or more load transfer modules may be used separately or in series. 
     A “substrate contact response” is the characteristics that remain in the substrate after a contact mechanics test has been performed. Each substrate contact response may contain,
     (i) a normal or tangential reaction force response   (ii) a normal or tangential displacement response   (iii) a “depth” which is the offset between the undeformed substrate surface and the distance of penetration of the stylus,   (iv) a “pile-up height” which is the offset between the undeformed substrate surface and the material that accumulates along the sides of the stylus above the original substrate surface,   (v) a “contact width” which is the peak-to-peak distance between pile-up heights which form on opposing sides of the stylus,   (vi) an “uncontacted substrate surface” which is the substrate surface that was deformed by movement of surrounding material but was not directly contacted by the stylus,   (vii) a “contacted substrate surface” which is the substrate surface that was deformed by engagement with the stylus through direct contact with the stylus,   (viii) a “microcrack” which is the creation of new surfaces in the substrate having an initiation position, length, and direction,   (ix) a “microstructural change” which is any change in the internal structure of the material. This includes, but is not limited to, the volume fraction of each crystalline structure, crystallographic and molecular texture, the free volume in the material, and the molecular arrangement,   (x) a “microvoid” which is the creation of additional space in the material such as crazes, interface debonding, and other phenomena generally associated with tension in the material, and   (xi) a “micromodification” which is any combination of microcracks, microvoids, or other noticeable changes in the substrate that is not a microstructural change.   

     A “substrate monitoring device” is an apparatus configured to allow for the measurement of one or more characteristics of the substrate contact response and/or the collection of material removed from the substrate. 
     A “field environment” is any location outside of a controlled laboratory setting which includes, but is not limited to, construction sites, manufacturing plants, trenches, repair or inspection facilities, but may also include locations on structures such as ships, bridges as well as any component of an assembly. 
     “Substrate surface preparation” is a method of removing large asperities and irregularities from the substrate surface through the use of physical or chemical processes such as etching, sanding, grinding, milling, and/or cleaning through traditional resources or guided tools. 
     “Substrate surface restauration” is a method of removing the substrate contact response from the substrate surface through the use of physical or chemical processes such as deformation, etching, sanding, grinding, milling, and/or cleaning through traditional resources or guided tools. 
     “Existing stresses” are stresses within a substrate which may arise due to existing service loads imposed on the substrate component and/or residual stresses from prior-manufacturing operations. 
     A “structural component” is any load bearing geometry which has been developed from a raw material, including but not limited to a plate, shell, pipe, I-beam, channel, angle, tubular sections, and more complex shapes that are cast, formed, machined or produced through additive manufacturing. 
     A “manufacturing process” is one or more steps used to produce and form a raw material into a fabricated structural component, including but not limited to casting, forming, heat treating, surface engineering and additive manufacturing processes. Examples of forming include rolling, bending and forging. Examples of surface engineering include shot-peening. Manufacturing processes can be further defined to include:
     i. A “permanent mechanical deformation” which arises due to tension, compression, or shear loading, in addition to localized processes such as shot-peening or abrasive wear. These processes cause greater strain hardening in regions of higher stress, and an associated change in mechanical properties.   ii. A “thermal load” which includes the input or removal of heat to expose a material to a specific temperature at a pre-defined rate, such as during casting or heat treating. The material condition gradients will then develop due to differences in temperature from the heating or cooling of the material, in addition to microstructural changes from phase transformation or grain growth.   

     A “material condition gradient” is the change, if any, in the material characteristics, material properties or existing stresses in the material. The “material condition gradient” is a function of position within the structural component, such as in the through-thickness direction. 
     “Material characteristics” include the microstructural parameters, such as grain size and chemical composition. 
     An “effective property” is a value which represents the overall response of the non-uniform material condition gradient existing within a structural component. This value is representative of the bulk material property of a greater sample volume that is measured through standardized testing methods, such as tensile, Charpy V-notch or fracture toughness testing. 
     “Local measurements” are indicators of material properties or characteristics obtained by probing a small volume of material. The material property may be a direct measurement or indirect estimation of yield strength, strain-hardening exponent, ultimate tensile strength, elongation, Young&#39;s modulus, hardness, and fracture toughness. Material characteristics may be the chemistry, the grain size or other microstructural characteristics. The indicators are obtained at a known location within a gradient. 
     A “computational model” is a numerical tool, such as Finite Element Analysis (FEA), finite difference methods or molecular dynamics, used to simulate the material condition gradient caused by the fabrication of a structural component with a known geometry using a specific manufacturing process and material model. 
     A “validation database” is a set of empirical test results where the technique has previously been used, with some of the previous testing including a verification that the predictions were correct by testing at multiple positions with respect to the material condition gradient. 
     An “algorithm” is a predictive function that is developed through a computational model, with or without additional calibration input from a validation database, to correlate local measurements with material condition gradients and effective material properties. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing features of embodiments will be more readily understood by reference to the following detailed description, taken with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic perspective view of a contact mechanics test apparatus according to exemplary embodiments. 
         FIG. 2  is a flow chart indicating the essential components of the apparatus according to embodiments of the present invention. 
         FIG. 3  is a schematic side view of a stylus with irregular geometry according to embodiments of the present invention. 
         FIG. 4  is a schematic side view of a stylus with axisymmetric geometry according to embodiments of the present invention. 
         FIGS. 5A-B  are schematic front views of a stylus and substrate contact response after deformation of the substrate by the stylus according to an exemplary embodiment. 
         FIG. 6  is a flow chart indicating the general process of developing algorithms with computational models, and using local measurements to predict material condition gradients and effective material properties for a structural component of known geometry and manufacturing process. 
         FIGS. 7A-B  are schematics detailing component geometry for exemplar embodiments of structural components. 
         FIG. 8  is a schematic demonstrating the change in initial material properties induced by manufacturing processes. 
         FIG. 9  is a schematic describing the relationship between local measurements along a material condition gradient in material properties. 
         FIGS. 10A and 10B  are schematics representing the use of a material condition gradient to obtain an effective property of a larger material volume measured through standard tests. 
         FIGS. 11A-C  are schematics of gradients in material properties induced by permanent plastic deformation from mechanical loading. 
         FIGS. 12A-C  are schematics representing the processes associated with the standard test method for performing a standard tensile test for pipeline components. 
         FIGS. 13A and 13B  are schematics of gradients in material properties induced by thermal loads by adding or removing heat to a structural component. 
         FIG. 14  is a schematic of combined effects from thermal and mechanical effects. 
         FIG. 15  is a schematic perspective of a stylus having a wedge-shaped profile. 
         FIG. 16  is a schematic perspective view of a stylus with a wedge-shaped, cutting tool profile engaging with the substrate. 
         FIG. 17  is a schematic side view of a contact mechanics test apparatus and path referencing alignment mechanism according to embodiments of the present invention. 
         FIG. 18  is a schematic side view of another exemplary contact mechanics test apparatus and path referencing alignment mechanism according to embodiments of the present invention. 
         FIG. 19  is a schematic perspective view of a contact mechanics test apparatus according to exemplary embodiments. 
         FIG. 20  is a schematic side view of a contact mechanics test apparatus and contact referencing alignment mechanism according to an exemplary embodiment. 
         FIG. 21  is a schematic front view of a contact referencing alignment mechanism for the apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. This includes exemplary testing apparatuses capable of performing both displacement and load control experiments. 
         FIG. 22  is a schematic front view of the contact referencing alignment mechanism of  FIG. 21 , showing a contact indicator according to embodiments of the present invention. 
         FIG. 23  is a schematic perspective view of an exemplary contact referencing alignment mechanism for the apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 24  is a schematic perspective view of another exemplary contact referencing alignment mechanism for the contact mechanics testing apparatus of  FIG. 1  according to embodiments of the present invention. 
         FIG. 25  is a schematic perspective view of another exemplary contact referencing alignment mechanism for the contact mechanics testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 26  is a schematic perspective view of another exemplary contact referencing alignment mechanism for the contact mechanics testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIGS. 27A-F  depict various schematic views of an exemplary testing apparatus with an alignment mechanism capable of contact referencing according to embodiments of the present invention. 
         FIGS. 28A and 28B  are schematic views of an exemplary rocking float subassembly according to embodiments of the present invention. 
         FIGS. 29A and 29B  are schematic views of an exemplary rocking float subassembly according to embodiments of the present invention. 
         FIGS. 30A and 30B  are schematic views of an exemplary rocking float subassembly according to embodiments of the present invention. 
         FIG. 31A-C  are schematic views of an exemplary rocking float subassembly according to embodiments of the present invention. 
         FIGS. 32A and 32B  are schematic perspective views of a contact mechanics test apparatus and contact referencing alignment mechanism according to an exemplary embodiment. 
         FIG. 33  is a schematic perspective view of an exemplary scanning referencing alignment mechanism for the contact mechanics testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIGS. 34A and 34B  are schematic side views of another exemplary scanning referencing alignment mechanism for the contact mechanics testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIGS. 35A-C  are schematic perspective view, front view, and side view, respectively, of an exemplary testing apparatus core capable of hosting two styluses according to embodiments of the present invention. 
         FIGS. 36A-C  are schematic perspective view, front view, and side view, respectively, of another exemplary testing apparatus core capable of hosting two styluses according to embodiments of the present invention. 
         FIG. 37  is a schematic perspective view of an exemplary normal force actuator for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 38  is a schematic perspective view of an exemplary normal force actuator for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 39  is a schematic perspective view of an exemplary normal force actuator for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 40  is a schematic side view of an exemplary normal force actuator for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 41A  is a schematic perspective view and  FIG. 41B  is a schematic side view of an exemplary portion of a frame engagement mechanism for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 42A  is a schematic perspective view and  FIG. 42B  is a schematic side view of an exemplary portion of a frame engagement mechanism for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 43  is a schematic top view of an exemplary portion of frame engagement mechanisms coupled to create multiaxial movement according to embodiments of the present invention. 
         FIG. 44  is a schematic top view of an exemplary core for stylus rotation according to embodiments of the present invention. 
         FIG. 45  is a schematic perspective view of exemplary frame and core engagement mechanisms for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 46  is a schematic top view of exemplary frame and core engagement mechanisms for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 47  is a schematic perspective view of exemplary frame and core engagement mechanisms for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIGS. 48A and 48B  are schematic views of an exemplary frame and frame engagement mechanism for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIGS. 49A and 49B  are schematic views of an exemplary frame and frame engagement mechanism for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 50  is a schematic view of an exemplary frame and frame engagement mechanism for the testing apparatus of  FIGS. 1 and 19  according to embodiments of the present invention. 
         FIG. 51  is a schematic perspective view of an exemplary substrate monitoring device for the testing apparatus of  FIG. 1  according to embodiments of the present invention. 
         FIG. 52  is a schematic perspective view of an exemplary substrate monitoring device for the testing apparatus of  FIG. 1  according to embodiments of the present invention. 
         FIG. 53  is a schematic cross-sectional view of an exemplary substrate monitoring device that monitors more than one substrate contact response feature according to embodiments of the present invention. 
         FIGS. 54A and 54B  are schematic perspective views, and  FIGS. 54C and 54D  are side view and front view, respectively, of an exemplary substrate monitoring device according to embodiments of the present invention. 
         FIGS. 55A-C  are schematic perspective view, cross-sectional perspective view, and bottom view, respectively, of an exemplary testing apparatus and substrate monitoring device according to embodiments of the present invention. 
         FIG. 56A  depicts a schematic perspective view and  FIG. 56B  depicts a schematic side view of an apparatus capable of substrate surface preparation according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     Overview of Apparatus, Methods and Applications 
     Provided in one embodiment is a contact mechanics test apparatus, as shown in  FIGS. 1 and 19 , configured to deform a substrate with at least one stylus, and the monitoring of the substrate response with at least one substrate monitoring device. In at least one embodiment, the apparatus may be also referred to as a testing apparatus, particularly when the apparatus is configured to perform a contact mechanics test. In one version of the embodiment, the deformation and the measurement device are part of a single sequence of travel on the substrate. The apparatus embodiment, as shown in  FIG. 19 , can be comprised of the following elements: a stylus  20 , a core  32 , a stylus engagement mechanism  41 , a core engagement mechanism  36  a frame  320 , a frame engagement mechanism  321  and a substrate monitoring device  39 .  FIG. 1  is a schematic diagram of an apparatus capable of performing a multi-directional frictional sliding test. This embodiment requires a test apparatus frame  320  which is fixed to the substrate surface  12  via the frame engagement mechanism  321  further comprised of supports  68  and mounts  38 , which may include magnets. The test apparatus frame  320  acts as a structural support for two displacement actuators  66 , which provide translational displacement to the core  32  along two perpendicular axes. This displacement is guided via two load transfer modules  35  and applied via two translation transfer modules  35 . In this embodiment, a yoke  316  is also utilized to transmit the translational and rotational displacements to the core  32  with respect to the substrate surface. A normal force is applied to the core  32  via normal force actuators  37 , which are coupled to a yoke  316 . The testing apparatus may also be configured to be portable so that it may be attached to existing large structures in a field environment, or may be used in small-scale laboratory testing. The apparatus provided herein simplifies, expedites, and improves the testing procedure in comparison to existing contact mechanics test apparatuses. 
     One novelty of the present apparatus over the prior art is the ability to perform stylus alignment with respect to the substrate surface through the use of an alignment mechanism  40  that adapts to the local substrate surface  16 . The impact of this novelty is that tests on a curved substrate can be done at different locations on the sample while ensuring that the alignment is the same at each of these locations. For a series of indentation tests, the stylus  20  is either aligned by the apparatus as it travels along the substrate surface  16  or aligned as needed prior to each indent. For a frictional sliding test, the stylus  20  is continuously aligned as it travels along the substrate surface  16 . The alignment mechanisms of the apparatus ensures stylus alignment for any in-plane substrate surface geometry, whereas prior art methods used two separate operations, deformation and surface scanning, to correct for curvature only in the direction of stylus translation. The alignment mechanism  40  can be embodied in a number of different ways which are discussed in detail later in this document along with demonstrative images. The general concept is to maintain reference of the apparatus with the substrate surface  16  when the stylus  20  moves along the surface (See Alignment Mechanism). Another novel feature of the apparatus is the shaping of one or more stylus  20  geometries to obtain different substrate contact responses. Some embodiments include multiple styluses  20 , to either gain more reliability in the response we measure, or to capture the response of different testing conditions at the same time. In general, the testing conditions produced by the stylus  20  or multiple styluses  20  have one or more purposes: to deform the substrate  10  to generate permanent deformation and/or time-dependent response characteristics and/or capture the built-in residual stress of the substrate  10 . Some embodiments can further have multiple cores. The specific embodiments for these different styluses  20  are further discussed after the general description of the testing methods and their effect (See Stylus). A summary of all of the essential components of the apparatus described herein is provided in  FIG. 2 . 
     One method is a novel use of contact mechanics testing to maintain a local angular orientation of a stylus  20  relative to the substrate  10 , engaging the stylus  20  with the substrate  10 , deforming the substrate  10 , and characterize the response of the material by measurement of the substrate contact response  12 . The testing apparatus may determine a full set of mechanical properties of a substrate  10  without destroying the function of the structure. In addition, the testing apparatus allows for the measurement of changes in local material mechanical properties along the length of deformation through characteristics of the substrate contact response  12 . 
     One method is a novel use of iterations of contact mechanic tests along with other physical measurements and analysis to predict property gradients and effective mechanical properties of a substrate based on substrate surface tests and additional manufacturing information available about the substrate. Although analysis techniques have previously been developed to perform a simulation of the effect of manufacturing on property gradients, the new method incorporates a combination of a series of laboratory tests to develop and validation the predictive equations, including the use of contact mechanic tests on cross-sections of representative samples. 
     The testing apparatus and methods may therefore be utilized for material property characterization in advanced small-scale fabrication, as well as in traditional industries involving welded structures, damaged structures, wear applications and other locations that are susceptible to failure. The testing apparatus and methods are also suitable as a tool for accurately probing mechanical material properties in manufacturing quality control, condition assessment, and diagnostic testing applications. The testing apparatus may provide a system configured to perform a testing method for evaluating mechanical properties of engineering, or structural, materials, including a measure of the strength, hardness, ductility, fracture toughness, charpy v-notch properties, fatigue resistance, and both existing and pre-existing stresses. The testing apparatus provides an apparatus and instrumentation to simplify the implementation of the testing method. It also allows for characterizing material anisotropy. 
     For many applications, mechanical properties of interest include yield strength, strain hardening behavior, ductility and toughness. Contact mechanics testing has recently been proven to allow users to accurately quantify the strength and ductility of metals and other materials. The ploughing of material during a contact mechanics test by a hard stylus  20  induces a steady flow of permanent deformation in the softer substrate  10 . The material displaced from the deformation is piled on both sides of the stylus  20 , and the piles have an identifiable height relative to the surface of the substrate  10 . The characteristics of the substrate contact response  12 , along with the reaction force from engagement between the stylus  20  and the substrate  10 , are used as inputs into reverse algorithms which output mechanical properties of the substrate  10 . 
     In addition to substrate mechanical properties, the testing apparatus and method are suitable for evaluating residual stresses that exist in the substrate prior to testing, as well as the intrinsic coefficient of adhesive friction for sliding contact between the material of the stylus  20  and substrate  10 . Additional applications include the quantification of time or rate-dependent material behavior, such as viscoelastic, viscoplastic, or strain-rate dependent properties. In other applications, the mechanical characterization may be combined with chemical and geometrical characterization techniques, such as non-destructive substrate thickness measurements. 
     In certain applications, the apparatus may be used to perform a series of indentation tests by using the same stylus engagement mechanism to apply the load and the core engagement mechanism to relocate the stylus  20  between indentations. 
     In other applications, a frictional sliding test is conducted in a machining mode to remove one or more ribbons or chips of material. These removed materials are collected using a substrate monitoring device  39 , and may be tested using existing methodologies for microstructure, chemistry, and mechanical properties. With this approach, more sophisticated laboratory testing techniques can be used to study a substrate  10  while only removing a superficial amount of material. 
     This apparatus and method will greatly impact practicing engineers and scientists, who can use the apparatus and method to obtain a quantitative assessment of the mechanical properties of substrates from assembled components. This allows for the measurement and prediction of the remaining service life in aging infrastructure and equipment without the removal of the substrate for traditional mechanical testing in a laboratory. In addition, the apparatus and method can be used on production lines to continuously perform quality control and assurance in manufacturing. These capabilities will greatly impact many professions, such as civil, mechanical, nuclear, naval, aerospace, and automotive engineering. The ultimate result will be greater confidence in the structural integrity and mechanical behavior of both newly manufactured and existing structures, promoting lower costs, less uncertainty, and greater public safety. 
     Following below are more detailed descriptions of various concepts related to, and embodiments of, a contact mechanics testing apparatus and a method of contact mechanics test. It should be appreciated that various concepts introduced above and discussed in greater detail below may be implemented in any of numerous ways, as the disclosed concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes. 
     Detailed Description of the Methods 
     The method of using the apparatus can be generally described as follows. Referring to  FIGS. 1, 3-5B, and 19 , a stylus  20  is forced to engage with a substrate  10  with the principal axis of the stylus  21  at a specified local angular orientation  23  to the substrate surface  16 . A novel characteristic of one of our methods is stylus alignment utilizing an alignment mechanism that maintains the stylus local orientation for a series of indentation tests and/or a frictional sliding test. Depending on the embodiment, the alignment mechanisms can be implemented by different components of the apparatus. When the method of stylus alignment is used for a series of indentation tests, it is important that the surface in the area of subsequent tests remains unaffected by contact of the apparatus. Similarly, the test results should not be affected by contact of the apparatus over an area of the substrate deformed in a prior test. This effectively allows for precise and efficient positioning of one or more styluses that are properly aligned with the local substrate surface for each test within the series. This is important for curved or irregular surface geometries where the local surface orientation changes as the stylus is repositioned along the substrate surface. 
     During a contact mechanics test, the stylus  20  engages with the substrate  10  through the stylus engagement mechanism  41  to deform the substrate  10  and create a substrate contact response  12 . The deformation of the substrate  10  may form piles  14  on one or both sides of the stylus  20 , which then remains as a characteristic of the substrate contact response  12 . During a frictional sliding test, the core engagement mechanism  36  further deforms the substrate  10  by moving the stylus  20  along the substrate surface  16 . During an indentation test, the core engagement mechanism  36  translates the stylus to different locations along the substrate surface  16  for additional tests. The amount of substrate deformation by the stylus  20  may be dependent on the geometry of the stylus  20  (e.g., the stylus included angle  22 ), the magnitude of the engagement load applied to the stylus  20 , physical properties of the substrate  10 , and the type of contact mechanics test (i.e. frictional sliding or indentation). The physical properties of the substrate  10  may be determined by analyzing the substrate contact response  12 . Other novelties of this method include how the material response is studied and how the stylus  20  is shaped and aligned to obtain specific responses. 
     An embodiment of the method includes utilizing data collected by the substrate monitoring device  39  of the contact width  24 , depth  26 , and pile-up height  28  along with reverse algorithms to predict the stress-strain curve of the substrate  10  and establish a quantitative index for the hardness, yield strength, ultimate testing strength, strain hardening behavior and elongation at break of the substrate  10 . 
       FIG. 5A  provides an example of an idealized substrate contact response  12  which may be expected in a substrate being deformed by a conical or pyramid-shaped stylus  20 . This substrate contact response  12  is typical of an indentation test or frictional sliding test in a ploughing mode to induce plastic deformation. Distortions of this profile occur from the relaxation of elastic strains from removing the stylus  20 , time-dependent strain relief like viscoelasticity or viscoplasticity, or the redistribution of existing stresses which may be caused by either existing service loads or prior manufacturing processes. In  FIG. 5B , multiple substrate contact response  12  profiles are shown. The contacted substrate surfaces, designated  250 ,  252 ,  254 , are in direct contact with the face of the stylus  20 , and the uncontacted substrate surfaces, designated  251 ,  253 ,  255 , are created by deformation of the substrate  10  being pushed around the stylus  20 . Profiles  250  and  251  represent the geometry of the loaded substrate, where the contact profile  250  matches the geometry of the stylus. Profiles  252  and  253  represents a substrate which has relaxed, with resulting changes in the depth  26 , pile-up height  28 , contact width  24 , and stylus included angle  22 . Profiles  254  and  255  represents a substrate that has experienced greater strain relaxation than profiles  252  and  253 . These measurements of deviations in substrate contact response characteristics may be utilized for predicting material properties related to strain relaxation. For a viscoelastic or viscoplastic substrate, profiles  250  and  251  represent the geometry under loading, profiles  252  and  253  represent the geometry after unloading, and profiles  254  and  255  represent the geometry a longer time after unloading. For a substrate with existing stresses, profiles  252  and  253  may exhibit the geometry of a substrate contact response parallel to the direction of maximum stress, and profiles  254  and  255  may exhibit the geometry of a substrate contact response  12  perpendicular to the direction of maximum stress where greater strain relaxation will occur. Additionally, regions  256  may undergo some form of micromodification. 
     Based on these observations of changes in the substrate contact response  12 , another embodiment of the method includes utilizing data collected by the substrate monitoring device  39  to predict the extent of existing service loads and/or pre-existing residual stresses. Loads (e.g., weight on a beam) induce stresses within a material during service in addition to residual stresses which remain from prior loading during manufacturing, e.g., welding. A common method for evaluating the magnitude of these existing stresses within a material is to measure the extent of elastic strain relief when those stress distributions are changed. For instance, this may be done by drilling a hole in the material and measuring the change in diameter of the hole from strain relief. For one embodiment, the apparatus is used to perform a contact mechanics test to change the existing stress distributions, and the strain relief may be observed by distortions from the idealized substrate contact response  12 , specifically deviations of the contacted substrate surface after the stylus  20  has been removed. In one embodiment, the directional nature of stress and strain is used to quantify the magnitude of existing loads. For example, a beam in bending has significantly greater stresses along its length than in the transverse direction perpendicular to its length. This understanding is used to examine the effects of the greater stress direction on the resulting substrate contact response measurements by performing a series of frictional sliding tests, including at least one in the direction of the anticipated maximum principal stress (e.g., length direction for a beam in bending or axial loading), and another roughly perpendicular to the first test in the direction of minimum principal stress (e.g., transverse direction), if these may be determined. The substrate contact response  12  from these deformations can then be directly compared to assess the extent of built-in or existing stresses within the substrate  10 . In another embodiment, the strain-relaxation of residual stresses may be quantified by examining the change in substrate contact response  12  geometry along the length of a single contact mechanics test. For example, when performing a contact mechanics test through a welded connection it can be expected that the area closest to the weld will contain significantly more residual stresses than the substrate  10  farther from the weld. This difference will be observed by measuring the differences in substrate contact responses  12 , where the greater release of elastic compressive strains in the area closer to the weld would lead to a closing displacement in the direction of the contact width  24 . 
     Another application of measuring deviations in the substrate contact response is for observing rate-dependent material properties such as viscoelasticity or viscoplasticity. This may be accomplished by performing contact mechanics tests at multiple speeds, using styluses with dissimilar geometries, or by repeatedly measuring the substrate contact response at different time intervals. 
     Another embodiment of these concepts is to compare the substrate contact responses  12  made with different engagement loads and stylus geometries, allowing for information to be obtained regarding the mechanical behavior of the substrate  10 . Consider, for example, a case where two simultaneous deformations were made at a fixed load and velocity, but one stylus  20  had an included angle  22  of 140° and a second stylus  20  had an included angle  22  of 170°. These two styluses  20  would create different amounts of deformation  11  in the substrate  10  and different strain rates. Being able to collect data on different amounts of strain would allow us to get more accurate yield (using the 170° included angle stylus) and strain hardening data (using the higher deformation 140° included angle stylus). Being able to compare strain rates allows viscoelastic deformation to be ascertained in materials where such behavior is possible and relevant. In this multi-deformation setup, the ability to adjust the engagement load on each stylus  20  would allow us to fine tune the stress-strain regime we are measuring, ranging from very low plastic strain at the yield point to extremely high strains for enhanced strain hardening data. Using various engagement loads allows for different penetration depths below the substrate surface  16 . By comparing the substrate contact response  12  from a low load (shallow) test and high load (deep) contact mechanics test, information concerning the gradients of existing stresses within the substrate  10  can be measured. These gradients through the thickness direction of a substrate  10  often exist from the manufacturing processes associated with forming a structural component from a raw material. 
     In addition to substrate  10  mechanical properties, the intrinsic coefficient of friction between the stylus  20  material and substrate  10  may be measured using embodiments of the apparatus and methods. This is accomplished through repeated frictional sliding tests performed at the same location within the substrate. During a frictional sliding test, the tangential load between the stylus  20  and substrate  10  is considered to contain two components, the adhesive component from friction which is dependent on the surface conditions of the materials in contact, such as roughness and lubrication, and the ploughing component which is dependent on the material properties of the substrate material and depth of penetration of the stylus. With repeated frictional sliding tests performed at a constant load, the ploughing component of the tangential load will go to zero and only the adhesive component remains, allowing for a simple description of the coefficient of friction between materials. The use of various lubricants may also be included in the experiment to assess the changes in friction coefficient. 
     In certain embodiments, the method may include a series of indentations in conjunction with frictional sliding tests. Such a method may be used, for example, for calibration and alignment verification. In other embodiments, the core is set to rotate during the contact mechanics test, such that the trajectory of the contact mechanics test changes in order to study the behavior of the substrate when deformed at different orientations. 
     Gradients and Effective Properties from Local Measurements 
     Material properties can be different at the substrate surface test location than within the substrate. The following new method enables the use of contact mechanics test results to predict the material condition gradients within a fabricated structural component as well as the effective property measured through standardized tests, including but not limited to tensile tests and contact mechanics. Material condition gradients arise due to existing stresses within the material, which occur due to the manufacturing processes required to fabricate a structural component from a raw material. These manufacturing processes include permanent mechanical deformation, thermal loads, or the combination of the two processes. The method may comprise the use of one or more local measurements that are input into predictive algorithms to obtain a material condition gradient as a function of position within the structural component. The algorithms are developed through computational models that simulate the creation of these gradients from an initially homogeneous material. These algorithms are verified and refined through the direct testing of material condition gradients via contact mechanics in the field and the laboratory. The models consider the changes in the material properties induced by manufacturing processes by including the relevant structural component geometry, mechanical or thermal loads, and boundary conditions. By considering multiple initial stress-strain curves, algorithms can be derived to correlate fabricated material condition gradients with the initial stress-strain curve. With this approach, a local measurement, obtained through a contact mechanics test or otherwise, is correlated to material properties throughout the structural component. In one embodiment, this local measurement is taken on the exposed surface of the structural component. 
     An effective property can be obtained from the material condition gradient through an additional computational model, such as the simulation of a tensile test with the material condition gradient, or analytical expressions through established techniques like homogenization theory. A validation database developed through prior empirical tests may also be used. 
     The general approach to predicting bulk mechanical properties from local measurements is provided in  FIG. 6 . Algorithms are developed based on a computational model specific to the type of manufacturing process, the structural component and standard test procedure, when a standard test equivalent is desired. The computational models and algorithms are validated against known databases built from field and laboratory test results. These algorithms are used to describe the changes in material properties from chemical and microstructural segregation, strain hardening from shape forming, and microstructural changes induced by manufacturing processes. Once these algorithms are developed, the application of the method no longer requires computational modeling; the inputs are the component geometry of the structural component and a local measurement, and the outputs are the material condition gradients and the effective property value. 
     Computational models are used to develop algorithms by simulating changes in material characteristics and/or material properties from the initial material to a fabricated material. This includes the true stress true strain material response in viscoelasticity or plasticity. It also includes approximations of changes in material characteristics as a function of the distance within the structural component, such as away from the surface. Computational modeling also offers the ability to predict residual stresses from forming and other prior or post manufacturing process. For example, residual stresses can be used and included in algorithms where contact mechanics is used to obtain and use indirect measurements of mechanical properties from the surface. Computational modeling and/or the algorithms can be improved using a validation database. This may include, for example, correction factors for expected material condition gradients that are typical for the application such as alloy and microstructure segregation. 
     The component geometry is dependent on the type of structural component as shown in  FIG. 7 , and can generally be described as the dimensions necessary to build a representative computational model. For the specific embodiment of a cylindrical pipe  FIG. 7A  this includes two parameters, the wall thickness  413  and radius  411 . For another embodiment involving a more complicated channel  FIG. 7B , three parameters describing the thickness  413  and lengths of the web  415  and flange  417  would be required. 
     Material models include equations on how the material characteristics and properties vary for different manufacturing processes. In  FIG. 8 , a metal or alloy material exhibits an initial stress-strain curve  419 . Manufacturing processes apply loading to the material  421 , which may or may not be subsequently removed  423 . These manufacturing process result in permanent plastic strain  425  if the material is loaded beyond the initial yield strength  427 . This causes a change in the mechanical properties of the material, such as an increase in the fabricated yield strength  429 . A stress-strain curve representative of the fabricated material  431  is shown along with the reloading segment  432  (offset for clarity). Other changes between the initial and fabricated material include the strain hardening behavior ( 433  and  435 ) and ultimate tensile strength ( 437  and  439 ). The changes in yield strength ( 427 ,  429 ), strain hardening ( 433 ,  435 ), and ultimate tensile strength ( 437 ,  439 ) may be inverse to what is shown in  FIG. 8 , depending on the type of manufacturing process. 
       FIG. 9  illustrates how a local measurement  0441 , obtained at a known location within a structural component  443 , can be related to a material condition gradient  445 . The shape and magnitude of the gradient  445  is dependent on dimensions of the structural component ( FIG. 7 ) and the changes to the initial material from manufacturing processes ( FIG. 8 ). Predictive algorithms are thus established to solve this reverse problem, where a unique solution will exist for a local measurement  441  obtained at a known location  543  for a given manufacturing process, geometry and initial stress-strain curve  419 . These predictive algorithms can be verified and refined with contact mechanics data from field and laboratory testing. The prediction illustrated by  445  could be directly compared to contact mechanics measurements across the range of normalized positions. In the case of a cylindrical pipe, this could be a measurement of material conditions across the full thickness of the pipe wall; from the outer diameter to the inner diameter. The prediction illustrated by  445  will vary due to metallurgical variations including grain size, processing history, and chemistry. These data will need to be confirmed via appropriate laboratory or field testing. Improvement of the algorithm requires iterative refinement based on knowledge of metallurgical variations and contact mechanics measurements of material conditions through the wall thickness. In one embodiment, the local measurement  441  may be obtained at the exposed surface of the structural component through a contact mechanics test. In another embodiment, the local measurement  441  may be obtained within the structural component through another suitable method. The embodiment shown in  FIG. 9  is for changes in normalized yield strength  447  as a function of normalized position  449  within the structural component. Normalized yield strength  447  is the ratio between the fabricated material yield strength  429  and initial material yield strength  427  that was shown on  FIG. 8 . Additional embodiments include other material properties such as strain hardening behavior, ultimate tensile strength, hardness, Young&#39;s modulus, and fracture toughness. The position may be through the thickness, or away from other features such as stress risers and welded seams. Normalized values allow for more general dimensionless predictive functions. 
     A material condition gradient  445  is shown within a structural component  451  in  FIG. 10A . In this embodiment, the relevant position is through the thickness of a plate geometry.  FIG. 10B  demonstrates how a tensile test on the structural component  451  homogenizes the material condition gradient  445  to obtain an effective property  457  representative of a greater sample volume. This process considers the full distribution of material properties to obtain a single representative value. Effective properties may be obtained through a computational model of a tensile test of the structural component with a material condition gradient, analytical equations through homogenization theory, or other suitable means. Specific embodiments of the general approach for different manufacturing processes are given below. 
     Embodiments of Manufacturing Processes 
     In one embodiment the algorithms are based on a computational model of permanent deformation from mechanical loads. An example is shown in  FIG. 11 , as the bending of an initially flat plate  459  with a specified thickness  413  into a curved shell or pipe geometry  463  with a known radius  411  ( FIG. 11B ). Bending may be accomplished through an applied moment  461 , four-point bending test, contact with a die, or other suitable means. The bending induces a material condition gradient  445  that is dependent on the distribution of strain through the thickness  413 . Material closest to the outer  467  and inner  469  diameters of the component have experienced the greatest change in material properties due to strain hardening, whereas almost no change has occurred near the mid-wall  471  where the material remains elastic or experiences the least permanent strain. If the bending load  461  is removed, elastic recovery  473  will occur resulting in a decrease in the measured material condition gradient  475  and increase in radius  477 . An application of this embodiment is the extraction of tensile test coupons from fully formed pipes  483  which is shown  FIG. 12A . Test coupons may be extracted from the longitudinal  479  or circumferential  481  direction of the formed pipe  483 . These tensile coupons may undergo additional manufacturing processes when the initial curved geometry  485  is pressed to a flat plate  489  between two parallel plates  487  moving in the direction shown by the arrows in  FIG. 12B . Flattening may occur through compression between rigid plates  487 , a bending moment, or other suitable means. Flattening results in additional changes to material condition gradients because of the permanent shape change from the curved pipe section  485  shown in  FIG. 7B  and the flat plate  489  section shown in  FIG. 12C . Although  FIGS. 11 and 12  represent permanent mechanical deformation of pipe or shell geometries, other manufacturing processes are also applicable. These embodiments include, but are not limited to, rolling, stamping, forging, bending and shot-peening. 
     In another embodiment, thermal loads are considered to induce material condition gradients, as shown in  FIG. 13 . One embodiment of thermal loads is the input of heat, as shown by the arrows in  FIG. 13A , to elevate the temperature of a structural component  451 . This is performed at a controlled rate and to a desired temperature. Fast heating rates will result in material condition gradients  445  from differences in thermal expansion. Other gradients may arise due to microstructural changes from sustained heating at elevated temperatures. One embodiment of this process is annealing, resulting in a decrease in the yield strength and increase in strain hardening exponent of the initial material. Another embodiment of thermal loads is the removal of heat, as shown by the arrows in  FIG. 13B , to reduce the temperature of a structural component  451 . Similar to rapid heating, the rate of heat extraction may induce significant material condition gradients  445  in the material. An embodiment of this process is quenching. An embodiment that considers both rapid heating and cooling is the deposition of filler metal during the construction of a welded joint. 
     In another embodiment, the effect of mechanical and thermal loading is coupled as shown in  FIG. 14 . This results in material condition gradients through similar mechanisms observed in the prior embodiments, however, the magnitude of these changes will generally be reduced. An example of this embodiment includes hot rolling and forming. 
     Detailed Description of Apparatus 
     Stylus 
     The stylus  20  profile that engages with the substrate  16  is what influences the substrate  10  response. As such, we can differentiate between different types of styluses  20  based on their produced response. Styluses intended to generate primarily permanent or time-dependent deformations in the substrate utilize a ploughing action. Referring again to  FIG. 5A , according to an exemplary embodiment, the stylus  20  has a conical geometry with a total included angle  22  between about 120° and about 170°, which corresponds to about 5° to about 30° of cone surface elevation with respect to the substrate surface  16 . The included angle  22  of the stylus  20  has an effect on the substrate contact response  12  during testing, and is selected based on the contact conditions, such as friction. The stylus  20  may have other types of geometries (not shown in the figure). For example, the stylus may be pyramidal, spherical, a wedge, or any other suitable geometries. For example, the stylus may have any suitable bottom cross-section, such as a triangular cross-section. In one example, the stylus  20  may be any commercially available shape, including Vickers, Rockwell, etc. The stylus  20  may be formed of any material with a sufficient hardness to penetrate the substrate  10  and form a deformation  11  in the substrate  10 , including, but not limited to, silicon, titanium oxide, sapphire, diamond, and steel with an appropriate coating or surface treatment. 
       FIG. 15  shows a wedge stylus configuration. Preferably, the stylus includes a blunted front as indicated by angles  270  and  271  to cause the plastic flow of the material without the formation of chips or the creation of dead-zones (areas where the material remains stationary with respect to the stylus) and, further downstream, has the ability to grab the material and push it away using a wedge  272  from the substrate contact response centerline to create enough biaxial tension to create the deformation. In one embodiment, as shown in  FIG. 16 , the wedge stylus  20  may be simplified to near triangular in order to use advanced machining techniques such as focused ion beam milling instead of other techniques such as additive manufacturing by laser sintering or other lithography techniques. A wedge stylus configuration will typically be shaped to enforce a machining or non-ductile response in the substrate  10 , resulting in chip or ribbon formation  750 . 
     Embodiments of Alignment Mechanisms 
     One category of embodiment is a path referencing system that is preset as part of the frame engagement mechanism before the contact mechanics test and guides the movement of the stylus to ensure that it maintains the desired local angular orientation with the substrate surface. In this category of embodiments, the core engagement can be contiguous with the frame. One embodiment of a path referencing alignment mechanism is a set of curved tracks that are fairly stiff and selected, for example, to be coaxial with the radius of a pipe. For a round pipe, the path referencing alignment mechanism can also be a track that has points of contact with the substrate surface and conforms and is normal to the local substrate surface. In the latter case, the surface can have multiple curvatures.  FIG. 17  shows a possible embodiment of the alignment mechanism  40  where a pre-set track  601  is configured to the geometry of the substrate surface  16  and allows for alignment of the core  32  (and stylus  20 ). In this embodiment, the track is rigidly attached to the substrate  10  of the component being tested. In another embodiment, as seen in  FIG. 18 , the conforming track  602  contacts the substrate surface  16  to match the geometry, but the contact does not require attachment that may damage the substrate  10 . In both embodiments, the direction of movement  200  of the core  32 , and therefore stylus  20 , is maintained by the respective path referencing embodiments of the alignment mechanism  40 . 
     Detailed Description of Contact Referencing 
     Referring now to  FIGS. 20-27B , a testing apparatus  30  is shown in detail according to several exemplary embodiments. As shown schematically in  FIGS. 20 and 21 , the testing apparatus  30  includes a core  32  to which the stylus  20  is coupled. The core  32  provides structural support for the apparatus by accommodating reaction forces on the stylus  20  from engagement with the substrate  10  and applied loads from the stylus engagement mechanism  41  and core engagement mechanism  36 . During a frictional sliding test, the stylus  20  is moved relative to the substrate surface  16  to deform the substrate  10  by applying an engagement load to the stylus  20  with a stylus engagement mechanism  41  and applying a transverse load to the core  32  with a core engagement mechanism  36 . During an indentation test, the stylus  20  is moved relative to the surface  16  of the substrate  10  to travel to different testing locations as part of a series of one or more indentations. According to an exemplary embodiment, the core engagement mechanism  36  is coupled to the core  32  with a transfer module  35 , shown as a mechanical link. The core engagement mechanism  36  may have a normal force actuator  37  that applies a normal force to the core  32  to maintain contact between the contact referencing alignment mechanism and the substrate surface  16 . The testing apparatus  30  may be coupled to the substrate  10  by a frame engagement mechanism  321 . As the deformation in the substrate  10  is formed by the stylus  20 , the testing apparatus  30  simultaneously measures the substrate contact response with a substrate monitoring device  39  coupled to the core  32 . The contact mechanics test and substrate contact response  12  measurements need not occur simultaneously. In one embodiment, these two processes may take place sequentially. In one embodiment, regardless of whether the two processes take place simultaneously or sequentially, the two processes are carried out by one single apparatus. Another embodiment involves multiple deformations being produced simultaneously with measurement of the substrate contact response which may occur simultaneously or sequentially. 
     Referring to  FIGS. 21-26 , a core  32  enables reliable monitoring and/or control of the position and principal axis  21  of the stylus  20  at a desired local angular orientation  23  to the substrate surface  16  of the substrate  10  at the same time that the deformation is being made. This process is referred to as contact referencing, and represents one embodiment of the alignment mechanism. The contact referencing alignment mechanism is configured to operate in either a monitor mode or a control mode. In the monitor mode, the core  32  allows the testing apparatus  30  to establish the local angular orientation of the principal axis of the stylus  20  under a predetermined applied engagement load with the substrate surface  16 , allowing for a load control experiment. In the control mode, the core  32  allows the testing apparatus  30  to form a deformation of a constant and known depth within the substrate  10 , and to detect the reaction force from engagement of the stylus  20  with the substrate  10 , allowing for a displacement control experiment. In either the monitor mode or the control mode, testing apparatus  30  induces deformation in the substrate  10 , resulting in a characteristic substrate contact response  12  which may be utilized with reverse algorithms to predict mechanical properties. 
     Embodiments of Contact Referencing 
     Embodiments include setting the local angular orientation of the stylus  20  based on a survey of the substrate surface  16  profile. This can be done with the use of contact floats  58 , as shown in  FIG. 32A  and  FIG. 32B . The floats are in contact with the substrate surface  16  and cause the core  32  (and stylus  20 ) to automatically re-orient with respect to the local substrate surface. As the local angular orientation of the stylus  20  is adjusted, the direction of the engagement load provided by the stylus engagement mechanism  41  is also modified. As discussed in detail below, the contact referencing may be implemented using floats. 
     According to exemplary embodiments, a core  32  may comprise two floats  58  ( FIG. 22 ), three floats  58  ( FIG. 23 ), four floats  58  ( FIGS. 24 and 27A ), or more, which contact the substrate  10  outside of the location being deformed by the stylus  20  in order to perform contact referencing alignment. Contact of the floats  58  with the substrate  10  is accomplished by applying sufficient load to the core  32 . For a two float  58  alignment mechanism, the floats  58  contact the substrate  10  at the same plane as engagement of the stylus  20  with the substrate  10  in the length direction of deformation. For a core  32  comprising three or more float  58 , additional floats are included either forward or rearward of the stylus  20  (e.g., in the direction of the deformation). In one embodiment, the core  32  may include a single member  60  positioned in line with the trajectory of the stylus  20  as shown in  FIG. 24 . In another embodiment, the core  32  may include two or more members  60  positioned rearward from the stylus  20  as shown in  FIG. 25 . The members  60  may be in line with the trajectory of the stylus  20 , or they may be positioned laterally, to the side of, the trajectory of the stylus  20 . The rearward members  60  and the members  60  positioned on either side of the stylus  20  may be utilized to reference the substrate surface  16  in the direction of the trajectory of the stylus  20 . In another embodiment incorporating three or more floats  58 , the span length between the stylus  20  and the front floats  58  and the span length between the stylus  20  and the rear floats  58  may be set at a predetermined ratio. This configuration allows for the correction of an irregular substrate surface with substantial curvature in the length direction and contact width  24  direction of deformation. For these embodiments, the floats  58  and stylus  20  are coupled by the core  32  to allow for the core  32  to be utilized in a monitor mode to perform load control or control mode to perform a displacement control experiment. 
     Referring to  FIG. 22 , the elevations  46  of the coupling members  60  of a two float  58  contact referencing alignment mechanism  40  are shown on either side of the stylus  20 . In control mode, the elevations  46  sets the relative offset between the stylus  20  deforming the substrate  10  and the floats  58  contacting the substrate  10  outside of the area being deformed, allowing for a constant and known substrate contact response depth  26  for a displacement control experiment. The same principles apply to contact referencing systems with more than two floats  58 , where contact between the multiple floats  58  and substrate  10  sets the penetration depth  26  of the stylus  20 . In monitor mode, the offset between the stylus  20  and floats  58  is not maintained, as the stylus  20  may translate in the direction of the penetration depth  26  based on the load applied by the stylus engagement mechanism  41  and the reaction force with the substrate  10  to perform a load control experiment. For this embodiment, the alignment mechanism  40  controls the local angular orientation but not the depth of the stylus  20 . 
     Cores  32  comprising 2 or more floats  58  in either monitor or control mode may allow for correction of the local angular orientation of the principal axis of the stylus  20  with the substrate  10 . For high load applications, the testing apparatus  30  is sufficiently rigid to transform the contact force between the substrate  10  and the floats  58  into a rotation of the core  32 . Local angular orientation may also be set by the predetermined lengths between the floats  58  and stylus  20  in the length and contact width  24  directions of deformation. In another embodiment, the local angular orientation is set by a transfer module  35  attached to the core engagement mechanism  36  that allows for low friction torsional rotation of the rigidly connected core  32  and core engagement mechanism. In low load applications, where the corrective torque provided by the core engagement mechanism to the core  32  is insufficient to provide local angular orientation correction, the core  32  may only provide elevation correction. Low load applications may include applications in which the contact force between the substrate  10  and the floats  58  is not translated into a rotation of the core  32 . Local angular orientation correction may not be needed when the substrate  10  and stylus  20  are set perpendicular or close to perpendicular (e.g., to within a few degrees of perpendicular) depending on the accuracy needed. Alignment using elevations  46  may reference the substrate surface  16  in a direction transverse to the direction of the deformation. 
     The floats  58  may include electrical contact indicators or contact load indicators  57  such that an error message may be provided if contact between the floats  58  and the substrate surface  16  is lost. The floats  58  may establish contact with the substrate surface  16  through frictional sliding, rolling contact, air flow or other contact mechanics mechanisms. The contact between the floats  58  and the substrate surface  16  may be elastic, although in some instances plastic contact may be possible. The floats  58  may be adjustable to allow for a change in the deformation depth. For example, in one embodiment, the floats  58  may be movable relative to static members  60  that are part of the core  32 . The floats  58  may be movable in a direction normal to the substrate surface  16 . Other directions of movement are also possible. 
     Two possible embodiments of a core configured for contact referencing alignment will include either three or four floats. The benefit to three floats is that, with sufficient normal force, all three will remain in contact with the substrate surface regardless of surface topography. However, mounting three floats symmetrically without interfering with the path of the frictional sliding test, which can cause premature surface deformation, or compromising stability, which may result in the core tipping, is a challenge. A core with four floats does not have this concern, but will have more difficulty keeping all floats in contact with the substrate surface at all times during a contact mechanics test, due to slight variations in float height or substrate surface topography, which can cause the core to suddenly rock between floats. One possible solution is to mount two of the four floats such that the effective point of contact is the average between them, determined mechanically.  FIGS. 28-23  show embodiments of the core  32  with a stylus  20  and two floats  58 , and a rocking float subassembly  300 , which includes two additional independent floats  302 . The rotation of the rocking float subassembly  300  is capable of keeping both independent floats  302  in contact with the substrate surface (not shown) during a frictional sliding test.  FIG. 28  shows an embodiment which includes an on-core attachment  304  to support the rotational attachment  52 .  FIG. 30  shows an embodiment which includes an off-core component  306  with an off-core attachment  308 , which the rocking float subassembly  300  and rotational attachment  52  can mount to independently of the core  32 .  FIG. 31  shows an embodiment that utilizes both an on-core attachment  304  and off-core component  306  with off-core attachment  308  to significantly increase the stiffness of the rocking float subassembly  300  and rotational attachment  52 .  FIG. 31  shows an embodiment which includes a pivot attachment  310  and two rocking float stabilizers  312 , though only one rocking float stabilizer  312  may also be used. 
     Embodiments of Scanning Referencing 
     Another embodiment for orienting the stylus, as shown in  FIG. 33-34B , performs a survey of the substrate surface  16  to gather surface topographic measurements using a topographic probe  43  and then actuate the core  32  (and stylus  20 ) using one or more translation actuators  67  as the stylus  20  travels along the substrate surface  16 . The topographic probe  43  can be mechanical, optical, and/or electromagnetic. The surface topographic probing can be done before and/or during the contact mechanics test. The core  32  is actuated by the core engagement mechanism  36  to rotate around one or two axes of rotation set approximately in plane with the local substrate surface  16  using information obtained from the scanned substrate surface  42 . The translation actuator  67  can be mechanical, hydraulic, electrical, or magnetically actuated. The selection depends greatly on the size-scale required for the testing objective. 
     Core 
     In some embodiments, the stylus  20  is supported by or continuous with the core  32 , which is a load bearing assembly accommodating reaction forces from the substrate  10  as well as applied loads from the stylus engagement mechanism  41  and core engagement mechanism  36 . Referring to  FIGS. 37-40 , the core  32  may be configured to provide lateral support to isolate the lateral frictional load from the engagement load reaction force on the stylus  20 . In one exemplary embodiment, as shown in  FIGS. 37 and 38 , the core  32  may include a rib  59  extending parallel to the trajectory of the stylus  20  and the direction of the deformation. The rib  59  may be a plate, gusset or other reinforcement. In another embodiment, as shown in  FIG. 40 , the core  32  may be configured to have an enhanced stiffness per weight—such as by altering the cross-section shape of the core  32 . In another embodiment, as shown in  FIG. 40 , the core  32  may include a brace  61 , extending between the stylus  20  and the core  32 . 
       FIGS. 27A-B  and  55 A-C show an example of a core  32  which is part of a testing apparatus  30  and substrate monitoring device  39 . The testing apparatus  30  may include floats  58  on the core  32  that supports the stylus  20 . A contact referencing alignment mechanism is shown in  FIG. 27C  with four floats  58 . The number of floats may be adjusted based on the application. Two of the floats  58  may be located closer to each other to avoid an intermittent three-point contact between the core  32  and the substrate surface  16 . The two floats  58  located closer together are shown at the front of the device, but may be located at the back of the device. The configuration shown in  FIG. 27C  provides more room for the substrate monitoring device  39 . The testing apparatus  30  may include one or more tension ties  101  to limit the tangential contact force between the stylus and the substrate.  FIGS. 27D-27F  provides an exemplar embodiment of tension ties  101  for a testing apparatus  30 . Floats  58  are not shown, but may be used. The tension ties  101  may comprise one or more slender cross-sections which are sufficiently strong to resist axial and shear loads but compliant enough to be flexible in bending. The testing apparatus  30  may be machined from a block, manufactured by etching methods, or constructed using 3D printing techniques, including laser sintering. A 3D printing method may be employed to form the testing apparatus  30  from steel, nickel alloys, or titanium. Other materials and fabrication techniques are also possible. The testing apparatus  30  may be formed from a unitary block of material. In one embodiment, the testing apparatus  30  may include a stylus engagement mechanism  41 , residual substrate measurement device  39  and core  32 , as described above, which may be integrated in one body, such as a unitary block of material. According to one embodiment, the testing apparatus  30  may include a core  32  formed from a unitary block of material. The unitary block of material may be formed by any suitable process, e.g., machining a block of material or building up the block of material through 3D printing. Portions of the testing apparatus  30  may have a surface coating or treatment providing increased wear resistance. The testing apparatus  30  may also include load transfer points  102  to maximize stability with the core engagement mechanism. The load transfer points  102  may be set between the stylus  20  and the rear floats  58  to help distribute the load between the floats  58 . The testing apparatus  30  may also include substrate monitoring device mounts  103  located on the side, bottom, and/or the top of the testing apparatus  30 . 
     In the testing apparatus  30 , the substrate monitoring device  39  may be mounted after the stylus  20  is installed. As shown in  FIG. 27B , the rear end of the testing apparatus  30  may be extended to host the substrate monitoring device  39 , protecting it from potential damage and providing locations for monitoring and measuring the substrate contact response  12 . Additionally, the substrate monitoring device  39  of other forms described above may be included within the testing apparatus  30 , either being attached to the core  32 , or utilized in a stand-alone system. 
     The testing apparatus  30  including multiple styluses  20  may also be utilized to perform multiple concurrent deformations  11  with varying engagement loads and varying stylus  20  geometries. A multi-deformation apparatus could be configured in a number of ways. Some embodiments can be seen in  FIGS. 35A-36C . In another embodiment, three floats  58  are used as a contact referencing alignment mechanism to maintain the local angular orientation of the styluses relative to the substrate surface  16 . Within the area of these three or more floats  58 , is one or more styluses  20 , each of which are free to move along their principal axis in the core  32  with a stylus engagement mechanism. The styluses  20  could each have the same geometry, or dissimilar geometries. Once the multiple deformations  11  are made, the mechanical properties can be calculated from measurement of the individual substrate contact responses  12 , but also from the comparison of the substrate contact response behavior relative to differences in stylus  20  geometry, engagement loads, sliding loads, or other variable factors. Multiple deformations  11  could be run concurrently or by multiple sequential contact mechanics tests using the same stylus  20 . In  FIGS. 35A-C , the center points of the stylus  20  are not aligned in the Y direction, as they are in  FIGS. 36A-C . The styluses are staggered in the Y direction and thus closer in X, bringing the deformations  11  closer together. By rotating the multi-stylus assembly, deformations  11  could be brought as close together as desired. In  FIGS. 36A-C , the closest the styluses  20  can be placed is the diameter of the bushings or bearings, or the styluses  20  themselves if no external bushing is added. The distance between the styluses  20  is equal to the distance between deformations  11 . In some instances, a minimum distance between deformations  11  must be observed to not have strain effects from the leading edge affect the trailing edge. However, strain effects could be measured on purpose by having the trailing edge within the strain hardened area produced by the leading edge. 
     In another embodiment, the apparatus consists of more than one cores, which host one or more styluses. A multi-core apparatus could be configured in a number of ways. For example, two or more cores may travel in parallel or they can travel in directions perpendicular to one another. The apparatus may use multiple core engagement mechanisms to connect to a single frame. 
     Stylus Engagement Mechanism 
     In one embodiment, the testing apparatus is configured to form a deformation in a substrate  10  using an stylus engagement mechanism  41  operating in either load or displacement control. If the stylus engagement mechanism  41  is operated in displacement control mode than the testing apparatus is configured to perform a displacement control test.  FIG. 22  shows an embodiment where the stylus  20  is fixed to the core  32 , the penetration depth of the stylus  20  is controlled and the stylus load with the substrate  10  is measured. In one embodiment, this is controlled by adjusting the elevation  46  of the alignment mechanism  40 , as discussed above. The stylus engagement mechanism  41  may constantly measure a component of the reaction force (e.g., normal or frictional reaction force) on the stylus  20 . The stylus engagement mechanism  41  may measure the stylus load by a variety of direct or indirect methods. In one embodiment, the stylus load reaction force is detected by monitoring the deformation of the stylus  20 , such as with a strain gauge detecting the strain on the surface of the core  32  or other component of the alignment mechanism, or by monitoring the change in height of all or a portion of the core  32 ; e.g., with linear voltage displacement transducers (LVDT) or optical sensors (such as a laser sensor, an inductance sensor, etc.). In another embodiment, the engagement load reaction force is detected with an in-line force transducer hosted within the core  32 . 
     The contact mechanics test may also be conducted in load control. In one embodiment, the stylus  20  may be movable relative to the core  32  through the use of a stylus engagement mechanism. Embodiments of the stylus engagement mechanism include a threaded connection, spring, piezoelectric element, dead weight, lever arms, piston or other means. For example, the stylus  20  may be coupled to a movable piston actuated by any appropriate method, including electromechanically, mechanically, hydraulically, pneumatically, etc. The apparatus described deforms the substrate with a fixed load, but is free to move vertically within the core  32 . As the apparatus is driven across the substrate surface  16 , the substrate contact response depth will vary according to the local mechanical properties of the substrate. Load controlled tests eliminate the need for monitoring the normal load of the stylus  20  during contact mechanics testing. This confers distinct advantages in contact mechanics testing over irregular surfaces, and in measuring changing properties in a single material, such as across a weld, encompassing base metal, the heat-affected zone, and the weld itself. The load controlled embodiment allows for multiple concurrent deformations to occur with varying engagement loads and varying stylus  20  geometries, which is discussed later as a specific embodiment of the core  32 . Furthermore, load control allows the stylus to travel over asperities that may exist on the substrate surface. 
     Normal Force Actuator for Contact Referencing 
     For apparatuses operating using a contact referencing stylus alignment mechanism, external loads must be applied to the core  32  to ensure engagement of the stylus  20  and/or floats  58  with the substrate  10 . Referring now to  FIGS. 37-41 , the normal force actuator  37  applies an engagement force to the core  32  and the stylus engagement mechanism  41  applies an engagement load to the stylus  20 . For a control embodiment, the engagement load is applied to the core  32  such that the load at the stylus  20  is greater than the reaction force between the stylus  20  and substrate surface  16 . The magnitude of the engagement load reaction forces is dependent on the substrate  10 , the geometry of the stylus  20 , and the residual substrate contact response depth  26 . As shown in  FIG. 37 , in one embodiment, the normal force actuator  37  includes a torsional spring  62 . The torsional spring  62  is anchored to a structure fixed to the substrate  10 , such as the core engagement mechanism  36 , and engages an arm applying an engagement load to a portion of the core  32 . In another embodiment, the normal force actuator  37  may include another mechanism, such as a linear actuator. As shown in  FIG. 38 , the normal force actuator  37  may include a translation actuator  67  coupled to a transfer module  35  that is anchored to the core engagement mechanism  36  and applying an engagement force to a portion of the core  32 . As shown in  FIG. 39 , the normal force actuator  37  in another embodiment may include a translation actuator  67  mounted to a transfer module  35  anchored to the core  32  and applying an engagement load to the core  32  through a transfer arm. 
       FIG. 40  illustrates a schematic side view of an embodiment of a core load applicator which uses one or more normal force actuators  37 , in this case four (one not shown), to apply a normal force to the core  32  via one or more multiaxial attachments  50 . The normal force actuators  37  may be coupled to a yoke  316 , which provides additional translational displacement and/or force application from the drive mechanism. The core  32  is shown connecting the stylus  20  and floats  58  to the multiaxial attachments  50 , though the stylus  20  and floats  58  may also be coupled independently of the core  32 . In this embodiment, the yoke  316  is shown mounted to a rotational displacement actuator  318 , which allows for controlled rotation of the core  32  independently of the displacements and forces being applied by the drive mechanism. These displacements and forces would be applied through the rotational displacement actuator  318  and yoke  316  to the core  32 . 
     Core Engagement Mechanism 
     According to an exemplary embodiment, the testing apparatus  30  is configured such that one or more core engagement mechanisms  36  may transmit translational motion to the core  32  and the stylus  20  while the core  32  and the stylus  20  may move independently of the core engagement mechanism  36  at a local angular orientation to the substrate surface  16 . The core engagement mechanism may be operated at multiple translational velocities, which will impose different strain rates into the substrate for a frictional sliding test. The core  32  may be coupled to the core engagement mechanism  36  with a transfer module  35 . In one embodiment, the transfer module  35  is configured to transfer translations to the core  32  from the core engagement mechanism  36  with pinned connections  63 . 
     Referring to  FIGS. 41A-42B , the core engagement mechanism  36  for providing translational motion along the substrate surface  16  is shown according to several exemplary embodiments. The core engagement mechanism  36  provides translational motion through the transfer module  35  without interfering with the alignment of the stylus  20  as prescribed by the core  32 . In other embodiments, the core engagement mechanism  36  may be coupled to the core  32  with another suitable connection. The translational motion may be applied with a lateral force in the pushing or pulling force; e.g., a force in a direction towards or away from the stylus  20 . According to an exemplary embodiment, the lateral force is applied with a displacement actuator  66  operating in the direction parallel to the substrate surface  16  being tested. The displacement actuator  66  may be any suitable mechanism (e.g., mechanical, hydraulic, pneumatic, electro-magnetic, etc.) capable of providing a sufficient force to overcome the friction resulting from the engagement load applied by the stylus engagement mechanism  41 . 
     Referring to  FIGS. 41A-B , the displacement actuator  66  acts upon a sliding guide  73 . The sliding guide  73  is held in place using support structures  68  and mounts  38  (for example, magnets  71 ), which may also act to align the sliding guide  73  with the desired load application point, e.g., the transfer module  35 . The load application point connecting the core engagement mechanism  36  to the core  32  is preferably positioned close to the substrate surface  16  to reduce the moment imparted on the stylus  20  when a sliding load is applied. This also prevents the effective reduction of the engagement load applied to the stylus  20  when a sliding load is applied. To provide stability in the core engagement mechanism, a plurality of mounting support structures  68  may be used at multiple locations along the sliding guide  73  path to guide an optional secondary sliding guide  74  connected to the sliding guide  73  by a connecting member  75 . Each of the mounting support structures  68  may be coupled to the substrate  10  by the frame engagement mechanism mounts  38 . 
     Referring to  FIGS. 42A-B , in another embodiment, the core engagement mechanism  36  may include multiple sliding guides  73 . The sliding guides  73  are held in place using multiple support structures  68  which also act to align each of the sliding guides  73 . The multiple sliding guides  73  may be connected by connecting members  75  such that they act in unison upon the desired load application point. In such an embodiment, the substrate monitoring device  39  may be included in the core engagement mechanism. 
     Referring to  FIG. 43 , in another embodiment, the testing apparatus  30  may include multiple core engagement mechanisms  36 , each with a different orientation, to move the core  32  (and stylus  20 ) through independent line trajectories, including a two-dimensional, non-linear trajectory. Each core engagement mechanism  36  may be coupled to one or more pinned connections  63 . Referring to  FIG. 44 , the core  32  may rotate through the use of bearings and a rotational core engagement mechanism  36  to maintain the local angular orientation of the core  32  (and stylus  20 ) with respect to the instantaneous direction of movement  200  of the core  32  (and stylus  20 ), and as such also the direction of the deformation  11 . 
       FIG. 45  shows a schematic isometric view of an embodiment of the apparatus drive mechanism capable of performing a multi-directional frictional sliding test. Two displacement actuators  66  apply a translational displacement to the core  32  via a yoke  316 . A rotation actuator (not shown) may also apply a rotational displacement to the core  32  via the yoke  316 . A normal force is applied to the core  32  and floats  58  by four normal force actuators  37  (one not shown). The displacement actuators  66  are coupled to sliding guides  73 , which may include translational attachments, and may be coupled to mounts  38 , and supports  68 . In this embodiment, each support  68  is fixed to the substrate surface  12  using magnets  71 . The core  32  and yoke  316  shown in this embodiment are presented in greater detail in  FIG. 40 . 
       FIG. 46  shows a schematic top view of the embodiment described in  FIG. 45 , except configured to operate with the use of secondary sliding guides  74 , which are coupled to the transfer module  35  by a connecting member  75 . The secondary sliding guides  74  provide additional stiffness to the transfer modules  35 . 
       FIG. 47  shows a schematic isometric view of another embodiment of the apparatus core engagement mechanism configured to increase the overall stiffness. In this embodiment, a displacement actuator  66  applies a translational displacement to the core  32  via a transfer module  35 . A normal force is applied to the core  32  and floats  58  via two normal force actuators  37 . The normal force actuators  37  are mounted to normal load actuator mounts  332 , which are coupled to the transfer modules  35 , which may include translational attachments, mounts  38 , and supports  68 . In this embodiment, the supports  68  are fixed to the substrate surface using magnets  71  as mounts  38 . 
     In another embodiment (not shown in figures), the testing apparatus may include a position measuring device that measures, with respect to the substrate surface or the alignment mechanism, the movement and position of the one or more reference points on the styluses. The position measuring device can be one or more of the following string potentiometer, encoder, LVDT, optical measurement device including confocal, photonic triangulation or spectral laser system. In certain modes, the displacement can be measured using a charge-coupled device (CCD). Other embodiments use the same measurement methodologies as used for the substrate monitoring devices. 
     Frame and Frame Engagement Mechanism 
     The testing apparatus is structurally supported by the frame and the frame is coupled to the substrate through the frame engagement mechanism. The frame engagement mechanism is further comprised of mounts which provide direct contact with the substrate and supports which provide a fixed or adjustable connection between the mounts and the frame. In one exemplary embodiment the frame and frame engagement mechanism are fixed rigidly to the substrate and provide structural support for the test apparatus as it is driven by the displacement actuators along a path of fixed distance. In another exemplary embodiment the frame and/or frame engagement mechanism are configured to move with the testing apparatus allowing for an infinite range of motion such as continuous testing around the circumference of a pipe. 
     Referring to  FIG. 48A-B , in another embodiment, the frame is configured as moveable object which follows a path around a circular substrate  10  set by the circular frame engagement mechanism  321 . The frame engagement can conform to circular substrates of varying diameter via the height adjustable mounts  38 . The frame  320  engages with the frame engagement mechanism  321  via the normal force applicator  37  and is driven around the circular path via displacement actuator  66 . 
     Referring to  FIG. 49A-B , in another embodiment, the frame  320  is fixed rigidly to the frame engagement mechanism  321  while the frame engagement mechanism  321  is translated around the circular substrate  10  via displacement actuator  66  mounted to the frame  320  and the wheel mount  38  opposite the core  32 . Normal force is applied to the core  32  through the normal force applicator  37 . The frame engagement mechanism  321  contains adjustments which all the device to conform to substrates  10  of varying diameter. 
     Referring to  FIG. 50 , in another embodiment, the frame  320  translates around the circular substrate  10  and is engaged with the substrate  10  via the mounts  38  and the frame engagement mechanism  321 , which is comprised of a cable  701  held in tension via a pulley  702  around the substrate  10 . The cable  701  provides flexible structural support for the frame  320  which is engaged with the frame engagement mechanism  321  via the normal force actuator  37 . The frame  320  is driven around the circular substrate  10  via pulley-style displacement actuator  66  to the frame. The frame engagement mechanism mounts to the substrate via mounts  38  which allow the frame to freely translate around the circular substrate  10 . 
     Portable Attachment Mechanism 
     One embodiment of the support  38 , shown in  FIGS. 41A-42B , may be a portable attachment structure that is configured to couple the testing apparatus to the substrate. In a field environment, there may be many mounting configurations necessary to collect the required data. For testing seam welded pipes, the mounting structure must accommodate performing a frictional siding test in the circumferential direction of the pipe. For butt-welded pipe, the mounting structure would have to allow the device to contact mechanics test along the length of the pipe. In other instances, such as on structural beams or bridges, the testing apparatus would have to mount securely to flat surfaces. In one exemplary embodiment for a portable testing apparatus, the mounting structure may include magnetic devices such as electromagnets similar to those utilized in mag-drills to create the contact, as well as high pressure suction, with a ferro-magnetic substrate. In some exemplary embodiments, the testing apparatus may be utilized in a field environment, and the material sample may be prepared (e.g., with a surface preparation) prior to a contact mechanics test. 
     Substrate Monitoring Device 
     In one embodiment, the substrate monitoring device  39  shown in  FIG. 1  is configured to collect ribbons or chips of material that are removed during a frictional sliding test performed in a machining mode. The substrate monitoring device  39  may consist of one or more components such that it is still capable of measuring characteristics of the substrate contact response  12 . This device is placed on the trailing side of the stylus and collects material removed from the substrate surface using one or more methods such as magnetic traction, suction or adhesion. In one embodiment, the material collection device is a wheel that engages with the substrate surface and picks-up the material removed. In another embodiment, suction is used to gather the material and storage is based on adhesion or the use of compartments. 
     In one embodiment, during a contact mechanics test, the substrate contact response depth  26  is known through the core  32 , and the engagement load reaction force on the stylus  20  is either controlled or measured. The substrate monitoring device  39  is configured to detect additional parameters of the substrate contact response  12 . Computer algorithms may be used to predict the physical properties of the substrate  10  using these measurements. As shown in  FIG. 21 , the substrate monitoring device  39  may be positioned behind the stylus  20 . In other embodiments, the substrate monitoring device  39  may be positioned under the stylus  20 , or be coupled to one of the trailing floats  58  of the core  32 . The substrate monitoring device may include both contact and non-contact devices. 
     The pile-up height  28  may be measured directly using at least one optical, electromagnetic, or mechanical method. Optical methods include laser confocal displacement meters, although other suitable methods are possible. The pile-up height  28  may be measured with a contact mechanism or a non-contact mechanism. When detecting the pile-up height  28 , the average of the pile-up heights  28  from each side of the substrate contact response  12  may be measured to simplify post-processing methods. 
     Referring to  FIG. 51 , according to one exemplary embodiment, the substrate monitoring device  39  may include a leaf spring  79 . The leaf spring  79  is coupled to the core  32  such that the distal end of the leaf spring  79  is positioned at or below the elevation of the stylus  20 . A protrusion  80  (e.g., a wedge or ridge) is provided at the distal end of the leaf spring  79 . The protrusion  80  is configured to contact the top of the piles  14  on either side of the substrate contact response  12 . The biasing properties of the leaf spring  79  may allow maintaining contact between the protrusion  80  and the piles  14 . The contact between the piles  14  and the protrusion  80  deflects the distal end of the leaf spring  79  upward. The magnitude of the deflection of the leaf spring  79  may be detected with a displacement transducer  81  located over the protrusion  80  and used to calculate the pile-up height  28 . The transducer  81  may be an LVDT, a plate capacitor, a piezoelectric unit, a laser sensor, an optical focus sensor, or any other suitable device. If included with a core  32  as part of device testing apparatus  30 , the profiles for the tracers may span from the front of the device towards the back and across the stylus  20 , and may have sufficient compliance to accommodate the entirety of a measurement range. 
     Referring to  FIG. 52 , according to another exemplary embodiment, the substrate monitoring device  39  may include a transducer  84  coupled to the core  32  in a generally vertical orientation. A mount  86  is disposed below the transducer  84 , proximate to the substrate surface  16 , and is coupled to the transducer  84  via a connection rod  83 . A wedge beam  88  is coupled to the mount  86  on a freely rotating pin  87 , the pin being oriented generally in line with the trajectory of the stylus  20  and the wedge beam  88  being transverse to the trajectory of the stylus  20  and extending across the contact width of the substrate contact response  12  such that it contacts the piles  14  on either side of the substrate contact response  12 . The magnitude of the deflection of the mount  86  may be detected with the transducer  84  and used to calculate the pile-up height  28 . The transducer  84  may be an LVDT, a plate capacitor, a piezoelectric unit, a laser sensor, an optical focus sensor, or any other suitable device. 
     In another embodiment, the measurement apparatus  39  may instead be configured to measure the contact width  24 . The contact width  24  may be measured with profilometry, or by direct imaging with a microscope or magnifying device. 
     As shown in  FIG. 53-54D , a substrate monitoring device  39  allows for monitoring additional information about the substrate contact response  12 . According to one embodiment, the substrate monitoring device  39  may include a combination of tracers. The tracers may be separate or combined by branching off from a larger tracer or another apparatus. A deformation center tracer  91  allows for monitoring the substrate contact response depth  26 , and the deformation center tracer  91  may have a smaller included angle than the included angle  22  at the center of the substrate contact response, as shown in  FIG. 54 . The deformation center tracer  91  may also identify and measure surface roughness and local variations caused by pores, inclusions and micromodifications in the material. A pile-up height tracer  92  may be similar to the one shown in  FIGS. 54A-B , but is utilized in conjunction with a substrate surface tracer  93 . The pile-up height tracer  92  and the substrate surface tracer  93  may be sufficiently compliant under torsion to ensure contact on both sides of the substrate contact response even in the presence of tilt. All tracers may be elastically preloaded to ensure sufficient contact pressure when the testing apparatus engages with the substrate. In addition, the contact pressure may be induced through other mechanisms; e.g., self-weight or air pressure. The pile-up height tracer  92  may have a protrusion  80  for pile-up contact, a pile-up tracer corner  96 , or a straight end. The substrate surface tracer  93  may have substrate surface tracer floats  97 , a straight end, or both. 
     The tracers, which are a part of the profile monitoring apparatus  90 , may be monitored through electronic, optical, mechanical and other like methods. Electrical methods may include monitoring capacitance, inductance, piezo-electric properties, or any combination of the like. Optical methods may include confocal and optical micrometry with the light source illuminating from any suitable direction, e.g., from the top or side. Mechanical methods may include the use of an LVDT or other displacement transducers. According to one embodiment, the instrumentation may be mounted to the substrate surface tracer  93 . An additional embodiment includes a tracer extension  98  for use with optical methods. Tracer extensions  98  may be mounted to the deformation center tracer  91 , the pile-up height tracer  92 , the substrate surface tracer  93 , or any combination of these to be used as reference point for monitoring and each respective profile property. Alternatively, the end of the tracers may be flat, to be used with, for example, optical methods such as with the use of confocal lenses. 
     As an alternative to the profile monitoring apparatus  90 , a 2D profilometer, either contact-based or optical, may be mounted to the testing apparatus  30  behind the stylus  20 . The 2D profilometer may allow for a full description of the substrate contact response. In addition, a laser confocal displacement sensor, or similar residual substrate measurement device  39 , may be utilized to obtain a complete description of the substrate contact response  12 . 
     Electronic Controls 
     In one embodiment, the test apparatus is configured with an electronic control system which may automate the motion of moving components of the test apparatus. The electronic controls may monitor motions of devices or test processes using electronic sensors and manage or direct their respective response. For example, the motion of the core may be monitored via position sensors and directed via the electronic controls, or the motion of the stylus may be monitored via a load cell and the electronic controls send commands to an actuator to maintain the desired tip force. 
     Substrate Surface Preparation 
       FIGS. 56A-B  show an embodiment of an apparatus utilizing a substrate surface preparation device  107 . Surface preparation may be utilized prior to performing a contact mechanics test, or subsequent to conducting a test to remove the deformation  11  from the substrate surface  16 . The apparatus may include a surfacing tool  104  mounted with or without a substrate surfacing tool tilt  105  to engage the substrate as guided by a surfacing referencing device  106 . The surfacing referencing device  106  may include a guiding tool  108  set having a set curvature. The substrate surface preparation device  107  may introduce a predetermined curvature to the substrate surface, which may also be corrected for by the alignment mechanism  40 . For example, a material sample curvature introduced by the substrate surface preparation device  107  may be corrected for by actuating floats  58 . 
     In one application, the substrate surface preparation allows for smooth transitions from the substrate to a weld. The substrate surface preparation device  107  may be based on abrasive techniques or machining, e.g., such as end milling. The detail of the surfacing tool  109  and the curvature of the surfacing referencing device  106  may be employed as an input to adjust the ratio of the span between the stylus  20  and the front floats  58  to the span between the stylus  20  and the rear floats  58 . 
     Substrate surface preparation is optional. In general, any type of processing to precondition the substrate surface  16  may be considered substrate surface preparation. In one embodiment, a surface preparation device allows for verifying and/or improving at least one condition of the material substrate surface  12  before a contact mechanics test is performed. According to one embodiment, the substrate surface may be lubricated to reduce the friction of the substrate surface and/or the variation of the friction of the substrate surface. According to some embodiments, sample surface rehabilitation is used to remove the deformation and changes on or beneath the substrate surface. This includes grinding, sand-blasting or polishing. It also includes sample surface rehabilitation devices based on machining processes similar to those that can be used for automated surface preparation that can be integrated with the main apparatus or used sequencially. 
     Multiple Apparatuses 
     The embodiments of the testing apparatus discussed above may be utilized as part of an assembly of multiple devices. These devices may be linked in series or parallel, and contain cores containing one or more styluses, various styluses, or various substrate monitoring device to measure various characteristics of the deformation imposed in a substrate through contact mechanics tests. The assembly of devices may be driven by one or more core engagement mechanisms. In another embodiment, a variety of testing apparatuses  30  may be provided, each having a different relative height between the floats  58  and the stylus  20 . 
     Fillet Welds 
     The testing apparatus  30  may be employed for the characterization of surfaces up to the toe of and through fillet welds and groove welds. For such an application, the floats  58  may be located behind the stylus  20 . According to one embodiment, two floats  58  may be located behind the stylus  20 . This arrangement allows the stylus  20  to approach a sloped portion of the weld. In some cases, two operations may be utilized to obtain the substrate contact response information up to the end of the trajectory of the stylus  20  when the floats  58  are located behind the stylus  20 . A first operation includes the formation of a deformation utilizing an alignment device  40 , and a second operation may include measuring the substrate contact response using an alignment mechanism  40 . Transverse markers may be added on the substrate surface  16  prior to forming a deformation to establish a relationship between the engagement load reaction force and the substrate contact response. To combine the two operations, the residual substrate measurement device  39  may be mounted opposite to the orientation shown in  FIGS. 51-54D . For example, the substrate monitoring device  39  may be attached at the rear of the testing apparatus  30  and the interaction with the substrate contact response may be just behind the stylus  20 . 
     Computer System 
     The testing apparatus  30  may be connected to, or include, an analysis system that is configured to predict or estimate the physical properties of the substrate  10  based on the measured data produced during the contact mechanics test. The analysis system may be a computing device. According to one embodiment, the testing apparatus  30  may be connected to an analysis system by a wired connection, wireless connection, a USB connection, or any other connection or combination of connection types. 
     SUMMARY 
     The testing apparatus  30  as described above provides a simple to implement and reliable method of performing a contact mechanics test to determine mechanical properties of a substrate  10 . The testing apparatus  30  is capable of performing a contact mechanics test and monitoring the inputs needed to predict mechanical properties. Further, through the use of an alignment mechanism  40 , the testing apparatus  30  may maintain a prescribed stylus orientation with respect to the surface throughout a contact mechanics test. The alignment mechanism  40  may also be utilized to monitor the undeformed substrate surface or control the local angular orientation of the stylus  20  through multiple methods. The testing apparatus  30  may control the engagement and sliding loads to accurately control the substrate contact response depth  26  during a contact mechanics test. 
     The testing apparatus  30  as described above is a relatively compact mechanism that is suitable for attachment to both portable and stationary implementations. This would allow for in situ testing of larger structures in a field environment with a portable device, as well as laboratory testing of smaller samples with a stationary device. The testing apparatus  30  can have a core engagement mechanism  39  capable of operating in either a push configuration or a pull configuration, and may be utilized with multiple core engagement mechanisms  39  based on the desired deformation, engagement load, sliding load, and substrate geometry. 
     The testing apparatus  30  described herein is able to continuously monitor the engagement load reaction force at the stylus  20  during a contact mechanics test. The testing apparatus  30  includes instrumentation to continuously measure the substrate contact response along the length of the deformation using both contact and non-contact methods. 
     A novel method is provided to obtain the material substrate response at different locations on the sample surface using a prescribed stylus alignment with respect to the sample surface. A novel method is also provided to infer about the property gradient and effective properties of the substrate. 
     Although the description contains the above specificities, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments of this invention. For example, the testing apparatus described may be incorporated within a continuous quality control system where deformations are used to monitor changes in material properties throughout production, such as a metal fabrication shop or automotive manufacturer. It should be noted that any of the components of the testing apparatuses described herein, or any of the steps of the testing methods described herein using the testing apparatuses described herein, may be operated manually or by a computing device. The operation by a computer device may, for example, be carried out through the execution of the computing device by an algorithm (such as through a computer program). Similarly, the algorithms described herein may be computer algorithms stored as software on a non-transitory computer-readable medium. A computing device may refer to any device that comprises a processor. In addition, the testing apparatus may be manufactured from a variety of materials including aluminum and brass, with various polymer covers to house the important instrumented components. The alignment mechanism and associated mounting components may be made smaller or larger based on the desired substrate contact response, engagement load, sliding load and substrate geometry. The core engagement mechanism may exist in many different embodiments such that it may be attached to portable or stationary systems. The testing apparatus described herein may be packaged as modular units to offer specific features such as enhanced measurement resolution or different deformation properties. According to one embodiment, the substrate contact response parameters may be monitored by an independent substrate monitoring device that is located behind, and follows, the stylus. Also, the testing apparatus may include an optional substrate surface preparation device which provides substrate surface preparation by milling, grinding, polishing or the like. Other embodiments include configurations specific to creating or measuring deformations specific to applications referenced above, including the parameters necessary to generate an uniaxial stress-strain curve and measure existing service loads. These embodiments may be linked together through a variety of means to perform multiple contact mechanics tests simultaneously or sequentially. Additionally, the methods described herein may further include using equations derived from a computer simulation, such as finite element analysis, to establish predictors for the yield strength, the strain hardening exponent, the ultimate tensile strength, and/or an index of the elongation at break. Other analytical methods, such as analytical algorithms, may be employed to derive material property parameters. 
     The above-described embodiments of the invention may be implemented in any of numerous ways. For example, some embodiments may be implemented using hardware, software or a combination thereof. When any aspect of an embodiment is implemented at least in part in software, the software code may be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers. 
     In this respect, various aspects of the invention may be embodied at least in part as a computer readable storage medium (or multiple computer readable storage media) (e.g., a computer memory, one or more floppy discs, compact discs, optical discs, magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other tangible computer storage medium or non-transitory medium) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments of the technology discussed above. The computer readable medium or media may be transportable, such that the program or programs stored thereon may be loaded onto one or more different computers or other processors to implement various aspects of the present technology as discussed above. 
     The terms “program” or “software” are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that may be employed to program a computer or other processor to implement various aspects of the present technology as discussed above. Additionally, it should be appreciated that according to one aspect of this embodiment, one or more computer programs that when executed perform methods of the present technology need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present technology. 
     Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments. 
     Also, the technology described herein may be embodied as a method, of which at least one example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments. 
     As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. 
     Although the above discussion discloses various exemplary embodiments of the invention, it should be apparent that those skilled in the art may make various modifications that will achieve some of the advantages of the invention without departing from the true scope of the invention.