bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Test Mode, Test Rate, Specimen Geometry, and Bending on Tensile Mechanical Behavior of a Continuous Fiber Ceramic Composite
Authors: Piccola JP , Jenkins MG , Lara-Curzio E
Published: March 2009

ASTM Test Method for Monotonic Tensile Strength Testing of Continuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-Section Specimens at Ambient Temperatures (C 1275) was used to investigate the effects of test mode (load versus displacement), test rate (fast versus slow), specimen geometry (straight-sided versus reduced-gage section), specimen volume (long/thin versus short/fat), and bending in tension for a twelve-ply, two-dimensional, plain weave SiC fiber reinforced / SiC matrix continuous fibre ceramic composite. Although it appeared that “graceful failure” is sometimes accentuated by displacement control at slow rates, a two-way analysis of variance (ANOVA) with replication at the 95% significance level of all the test results showed that there was no significance of test rate, test mode or specimen geometry for proportional limit stress. Similarly, for ultimate tensile strength there was no significance of test rate or test mode although there was a significance of specimen geometry. Finally, for this two dimensional, plain weave fiber architecture there was no significance of test rate, test mode, or specimen geometry (including straight-sided specimens) on fracture location. Proportional limit stress decreased with increasing bending while ultimate tensile strength appeared independent of bending.
Shear Strength of Continuous Fiber Ceramic Composites
Authors: Lara-Curzio E , Ferber MK
Published: March 2009

The applicability of ASTM Test Method for Shear Strength of Continuous Fiber-Reinforced Advanced Ceramics at Ambient Temperatures (C 1292) was investigated to determine the shear strength of one-dimensional and two-dimensional continuous fiber-reinforced ceramic composites. The advantages and disadvantages of the test method are addressed, and the effect of notch separation on the measured interlaminar shear strength by the compression of double-notched specimens are discussed. Experimental results are presented for the interlaminar and in-plane shear behavior of two-dimensional Nicalon™/SiC and the interlaminar shear strength of one-dimensional carbon/carbon composites both at room temperature and 1000°C. The effect of fiber coating thickness on the interlaminar shear strength of two-dimensional Nicalon™/SiC is also discussed.
Tensile and Fatigue Behavior of a Silicon Carbide/Silicon Carbide Composite at 1300°C
Authors: Ünal Ö
Published: March 2009

Monotonic and fatigue properties of a silicon carbide/silicon carbide composite were studied at 1300°C in tension. All tests were conducted in nitrogen (N2) to eliminate oxidation. Because of the composite architecture and the differences between matrix and fiber properties, the composite failure under both monotonic and cyclic loads took place in stages. In a monotonie test, the composite failure occurred by the creep of bridging fibers, and thus, fibers displayed nonbrittle fracture features. In fatigue tests, although creep was also occurring under cyclic loads, the fracture surface analysis showed that final fracture took place in a brittle manner.
Stress-Temperature-Lifetime Response of Nicalon Fiber-Reinforced Silicon Carbide (SiC) Composites in Air
Authors: Lin H-T , Becher PF
Published: March 2009

Time-to-failure tests were conducted in four-point flexure and in air as a function of stress levels and temperatures to study the lifetime response of various Nicalon fiber-reinforced silicon carbide (designated as Nic/SiC) composites with a graphitic interfacial coating. The results indicated that all of the Nic/SiC composites exhibit a similar stress-dependent failure at applied stress greater than a threshold value. In this case, the lifetimes of the composites increased with decrease in both stress level and test temperature. The lifetime of the composites appeared to be relatively insensitive to the thickness of graphitic interface layer and was enhanced somewhat by the addition of oxidation inhibitors. Electron microscopy and oxidation studies indicated that the life of the Nic/SiC composites was governed by the oxidation of the graphitic interfaces and the formation of glass(es) in composites as a result of the oxidation of the fiber and matrix, as well as any inhibitor phases.
Fatigue Crack Growth Behavior of a Woven HPZ/Silicon Carbide Ceramic Matrix Composite
Authors: Kramb VA , John R
Published: March 2009

This paper discusses the results of an investigation of the fatigue crack growth behavior of a silicon-nitrogen-carbon-oxygen/silicon carbide (HPZ/SiC) ceramic matrix composite containing an 8 harness satin weave fiber architecture. Crack growth during the tests was monitored using optical and scanning electron microscopy as well as specimen compliance. The fatigue crack growth behavior of the composite and the monolithic matrix was used to characterize the fiber bridging mechanism during fatigue loading. A shear lag crack bridging model was used to deduce the fiber/matrix interfacial shear stress during the crack propagation. The effect of fatigue loading on the predicted fiber bridging stresses and crack opening displacements are also discussed.
Characterization of Damage Progression in Ceramic Matrix Composites Using an Integrated NDE/Mechanical Testing System
Authors: John R , Buchanan DJ , Stubbs DA , Herzog JA
Published: March 2009

This paper discusses the use of an unique integrated Nondestructive Evaluation (NDE)/Mechanical test system to characterize the damage progression in a ceramic matrix composite (CMC) under tensile and fatigue loading conditions. During the tests, the effects of damage were characterized in situ using conventional extensometry, and ultrasonic surface and longitudinal wave transducers. The surface wave technique clearly identified the proportional limit of the composite, while the longitudinal wave technique captured the overall deformation behavior during the tension tests. Both ultrasonic NDE techniques showed equal or greater sensitivity to damage progression in the CMC compared to conventional extensometer-based modulus data.
On the Optimal Design of Fiber-Reinforced Laminates
Authors: Kalamkarov AL
Published: March 2009

The optimal design of the fiber-reinforced laminates is based on the application of the general homogenization model for the composite shell developed earlier by the author. The optimal design algorithm for the fiber-reinforced laminates with the prescribed set of effective stiffnesses is developed. The set of prescribed effective stiffnesses for which the design problem is solvable, is described, and the effective method of the design parameters calculation based on the convex analysis is developed. The sufficient number of plies required for the design of the fiber-reinforced angle-ply laminate with the prescribed set of effective stiffnesses is determined. The design problem is generalized on account of minimization of the fiber volume content. The effectiveness and advantages of the developed approach are illustrated by several design examples.
Testing within the Continuum of Multiple Lubrication and Failure Mechanisms
Authors: Wedeven LD , Totten GE , Bishop RJ
Published: March 2009

The inherent difficulty of bench testing for the tribological performance of hydraulic fluids is the interaction of multiple lubrication and failure mechanisms. The engineer judges the performance limits in descriptive terms relating to what the load bearing surfaces have experienced. The lubrication and failure pathway that leads to the final surface condition is at the mercy of what lubrication and failure mechanisms have been invoked. Lubrication mechanisms, such as hydrodynamic, elastohydrodynamic, and boundary can be isolated with specialized testing, along with failure mechanisms, such as those described in general terms of wear, scuffing, and pitting. The interaction and competitive nature of these mechanisms, which exist in hardware, makes bench testing a nightmare.

A rational approach using a highly flexible and computerized test machine, WAM3, is described. The approach demonstrates how performance attributes of fluids and materials can be evaluated as they are made to travel through multiple lubrication and failure pathways. The testing protocol is terminated when the test specimen's surface reaches the same failure condition the engineer uses to judge performance limits of component hardware. Testing pathways are demonstrated that lead to wear, scuffing and micro-pitting. Along the testing pathway, viscous film-forming attributes and chemical boundary lubrication attributes of the fluid are characterized. Tests conducted with a range of fluid types, including two hydraulic fluids, demonstrate a wide range of traction, viscous film-forming and boundary film attributes. The continuum approach, which maps out performance in terms of hardware relevant criteria, provides a means to determine the impact of development strategies based on fluid and material technologies.
Pump Testing Strategies and Associated Tribological Considerations-Vane Pump Testing Methods ASTM D 2882, IP281, and DIN 51389
Authors: Reichel J
Published: March 2009

Various test methods have been developed to determine the performance limits of various classes of hydraulic fluids. Lubrication capacity depends on various fundamental fluid parameters including viscosity and anti-wear properties. Critical elements of hydraulic pump and motor lubrication, which is characterized by sliding line-contact wear, will be discussed here. In vane pumps, the pressure loaded tips of the vanes are under Hertz-type load in contact with the surface of the cam ring, and rotate at a high speed creating a sliding line-contact. Due to this sliding line contact, the vane pump is the best-suited instrument for determination of the anti-wear performance of hydraulic fluids within acceptable time and at reasonable expense.

Alternatively, hydraulic pump and motor testing may require greater energy, 150 kW or more over a period of more than 1000 hours significantly increasing the cost of testing. Furthermore, tests on smaller versions of one type of pump or motor do not necessarily correlate with larger units of similar design. Therefore, it would be desirable to develop a laboratory test that: utilizes a rig with standard wear parts, provides a selective method for identifying various forms of lubricant failure, and that permits tests correlation with a wide variety of hydraulic pumps and motors used in the industry today.
Section D02.N.7 Status Report on Vickers 20VQ5 Vane Pump Test Development
Authors: Nahumck WM , Marougy T
Published: March 2009

Concerns about operational difficulties with the ASTM D2882 Test Method and whether the Vickers 104C vane pump will be continued in production has prompted the need to develop a replacement test for the ASTM D2882 Test Method. ASTM Section D02.N.7 has been investigating for the last five years such a potential replacement test using the Vickers 20VQ5 vane pump. The goal is to develop a replacement test that uses a pump of current and expected future manufacture that will provide results consistent with results obtained previously using the D2882 Test Method. The initial study that was the basis for test development was originally published in May 1992 in the STLE publication, “Lubrication Engineering”. Since that time there has been an ongoing effort to complete a comparison using four (4) reference oils in nine (9) laboratories, including European participants. Difficulties and problems related to test operation and test cartridge preparation have occurred and are reviewed in this paper.
Evaluation of Vickers V-104 and 20VQ5 Vane Pumps for ASTM D-2882 Wear Tests Using Water-Glycol Hydraulic Fluids
Authors: Totten GE , Bishop RJ
Published: March 2009

Work is currently underway within the ASTM D.02 N.07 “Hydraulic Fluid Testing” Committee to evaluate the potential of replacing the Vickers V-104 vane pump with a newer, more current model, 20VQ vane pump for use in an updated ASTM D-2882 and other national standards. All of the round robin work conducted within the committee thus far has involved the use of non-aqueous hydraulic oils. Although there are some significant inter-laboratory reproducibility problems, it appears that the overall ranking of the hydraulic oils by most laboratories appears to be consistent.

To further evaluate the potential utility of replacing the Vickers V-104 pump with the 20VQ pump, a series of different water-glycol hydraulic fluid formulations with significantly different wear rates were evaluated using a “modified” ASTM D-2882 testing procedure. The results showed that expected catastrophic pump failures, which occurred with the V-104 pump, not only did not occur with the 20VQ pump, but the relative orders of wear rates for some of the fluids were also different.

In this paper, a brief history of the development of the ASTM D- 2882 test, as currently conducted, will be presented, a comparison of the features of the V-104 and 20VQ pump and cartridge assemblies will be given and a comparative tabulation of the pump test using the V-104 pump and the 20VQ pump using different testing conditions will be provided. Finally, recommendations for future work will be made.
Standardized Hydraulic Fluid Testing — an Overview and History
Authors: Jackson JM , Marty SD
Published: March 2009

In order for a hydraulic fluid to be approved by the various pump manufacturers for use in their products, it must qualify for acceptance according to certain test methods. Chief among these tests are the Denison HF-0, the Vickers 35VQ25, and the John Deere Sundstrand piston pump test.

The Denison HF-0 test evaluates hydraulic fluid performance based on flow, deposits, and wear in both a Denison P46 axial piston pump and a Denison T5D vane pump. Both pumps are run for 100 hours and are periodically disassembled for inspection. Obtaining satisfactory pump results is the largest step in the process for a fluid to qualify under the HF-0 Standard. In the past, the P46 and T5D pumps could be tested separately or “bootstrapped” with a 46 series motor to reduce horsepower requirements.

The Vickers 35VQ25 test measures the anti-wear characteristics of a hydraulic oil according to cam ring and vane weight loss in a 35VQ25 vane pump. A minimum of three cartridges are tested for 50 hours each. The first three, or four of five cartridges, must perform satisfactorily in order for a fluid to pass this test.

The John Deere piston pump test screens oils that cause corrosion of copper containing metals. A Sundstrand 22 series axial piston pump is operated for 25 hours. Water is then added to the test oil. The test is then run for 200 more hours. Over this time multiple parameters are monitored to determine the effect of the added water.
Testing Method for Biodegradable Hydraulic Pressure Media Based on Natural and Synthetic Esters
Authors: Remmelmann A
Published: March 2009

This article describes a special test procedure for biodegradable fluids based on natural and synthetic esters and gives results of their examination. The test allows the evaluation of the special properties of these fluids, e. g. hydrolytic stability. By using a long endurance test, the fluid's behaviour during its use can be examined. The test rig works with serial hydraulic components. The loads are higher than in practice applications in order to reduce testing time. Therefore the results are transformable to practice and it is possible to give a precise description of the fluid's behaviour. The change of the fluid's properties and the ageing behaviour can be determined by analysing samples. With this knowledge the technical performance of the fluids can be improved, by changing additive packages or base fluid types.
A Review of Four-ball Methods for the Evaluation of Lubricants
Authors: Perez JM
Published: March 2009

A review of four-ball wear tester and test methods developed at Penn State by Prof. Emeritus E.E. Klaus (Deceased) and students of Klaus. The test methods include standard methods for fluid and additive evaluation, microliter tests to evaluate tribochemical reactions in the contact zone, Ball-on-Three Flat tests to evaluate materials and fluids, scuffing test methods and sequential four-ball tests, one of which was developed to screen hydraulic fluids for full-scale pump stand tests and field vehicles. Applications range from room temperature to over 425 °C. The variety of methods demonstrate the versatility of the FBWT, including applications related to the tribology of hydraulic fluid systems.
The Physics of Baseball; the Standardization of Balls and Bats for Recreational Softball
Authors: Adair RK
Published: March 2009

An analysis of the effects on ball velocity and flight of the development of highly elastic softballs and bats suggests that it is necessary to constrain the elasticity of ball and bat to preserve the integrity of slow-pitch softball and to ensure the safety of the players.
Dynamic Hardness (SDH) of Baseballs and Softballs
Authors: Giacobbe PA , Scarton HA , Lee YS
Published: March 2009

Impact research of soft materials has led to a new general dynamic hardness test method and hardness scale entitled the Scarton Dynamic Hardness (SDH) Method. Experimental impulse modal analysis testing is used to evaluate the transient or response characteristics of test materials such as sports equipment. The SDH method was used to evaluate and classify different types of sports balls by dynamic hardness and damping. A direct relationship was found between ball damping and the coefficient of restitution (COR). Sports safety applications show that a ball with a lower SDH has a reduced chance of inflicting head injury; if the SDH is too low, chest impacts may contribute to heart anomalies. Acoustical and impacter design research indicates that keeping the impacter resonances above the ball SDH will prevent their excitations. Subsequent reductions in acoustic “pinging” and enhanced performance are anticipated. The study included: baseballs, softballs, golfballs, racquetballs, marbles, ping pong, bowling, lacrosse, cricket, bocce, squash, tennis, and billiard balls.
Creep Damage and Creep-Fatigue Damage Interaction Model for Unidirectional Metal-Matrix Composites
Authors: Kruch S , Arnold SM
Published: March 2009

A multiaxial, isothermal, continuum damage mechanics model for creep and creep-fatigue interaction of a unidirectional metal-matrix composite (MMC) volume element is presented. The model is phenomenological, stress based, and assumes a single scalar internal damage variable with directional-dependent evolution. The present creep damage model is an extension of the Leckie-Hayhurst creep damage model to unidirectional MMCs and is shown when taken to its isotropic limit, to directly simplify to this previously developed and validated isotropic creep damage model. This extension is accomplished by introducing into the isochronous damage function physically meaningful stress invariants that reflect the local stress and material orientation within a metallic, transversely isotropic material (for example, hexagonally packed unidirectional metal-matrix composite). These invariants are included based on the anticipation that the associated stress may strongly influence void growth at the fiber-matrix interface (as this interface is postulated to play a role, on the mesostructural scale, analogous to that of grain boundaries on the microstructural scale and interfacial degradation); and, consequently may correlate with a creep rupture mechanism based on interfacial degradation through diffusion-related void growth.

Creep-fatigue interaction is accomplished by directly adding together the mechanical effects of creep and fatigue damage. A uniaxial parametric study is performed under pure creep and creep-fatigue conditions, to demonstrate the sensitivity of the various material parameters and the capability of the formulation in attempting to characterize a class of composite materials. Specifically, two interaction regions will be examined, the first being important for low-frequency loading cycles (<5 Hz) and is termed “creep-dominated” interaction; whereas the second is for high-frequency loading cycles with a non-zero mean stress, and is termed “fatigue-dominated” interaction. Results are presented in the form of S-N and damage accumulation curves.
A Model for Predicting the Effect of Environmental Degradation on Damage Evolution of Metal-Matrix Composites
Authors: Allen DH , Foulk JW , Helms KLE , Lagoudas DC
Published: March 2009

A life prediction model is being developed by the authors for application to continuous fiber metal-matrix composites (MMCs). The specific systems considered in this study are silicon-carbide fibers imbedded in titanium matrix. Due to multiple nonlinearities, the model utilizes a computationally based framework derived from thermodynamics and continuum mechanics. Matrix inelasticity, damage evolution, and environmental degradation due to oxidation-related effects are also included within the model. To computationally implement the model, the finite element method is used with an evolutionary analysis of a unit cell accomplished via a time-stepping algorithm. Matrix inelasticity is modeled with the Bodner anisotropic hardening viscoplastic model. Damage growth such as fiber-matrix debonding, surface cracking, and matrix cracking is modeled via the inclusion of cohesive zone elements in the unit cell. The locations of these elements are chosen to correspond with experimentally observed damage. As environmental degradation varies in form, depending on the specific system, it is accounted for by including either an outer surface layer that is embrittled due to oxidation or degraded material properties that result from oxygen-induced changes in microstructure.

The current paper outlines the formulation utilized by the authors to solve this problem, and recent results are discussed. Specifically, results are given for a four-ply unidirectional composite subjected to monotonic and fatigue loadings. In both cases, environmental degradation influences the initiation and evolution of damage.
Microscopic and Mesoscopic Damage Localization
Authors: Agha YH , Hild F , Billardon R
Published: March 2009

Initial defects are the main cause of the failure of structures made of brittle or quasi-brittle materials. The aim of this paper is to model within the framework of continuum damage mechanics these defects and their influence on the mechanical behavior of the structure they lie in by using a strain localization criterion. The microscopic and mesoscopic conditions for localization are studied by utilizing isotropic or anisotropic damage variables. A representative volume element (RVE) containing one defect is defined and the failure criterion of such an RVE is derived. The initial defect is modeled by an initial damage parameter. The evolution law of this damage value depends upon the nature of induced damage. Finally, an extension of this study to the case of high-cycle fatigue is proposed.
Effects of Damage Distribution on Evolution
Authors: Lacy TE , Talreja R , McDowell DL
Published: March 2009

Recent micromechanically inspired phenomenological theories using internal state variable (ISV) representations of damage have been used to predict the thermomechanical behavior of microcracked solids. These models do not, in an explicit manner, account for distributions of microcracks in a representative volume element (RVE) and have been used successfully only to determine the effective moduli of damaged solids. It has been demonstrated that while the distribution and interaction of damage entities within an RVE generally have a minor effect on the effective moduli, it has a significant effect on the evolution of damage and failure at the macroscale. Damage evolution rates, in general, cannot be described adequately by such theories because of their inability to account for interactions between damage entities in an arbitrary distribution.

Key issues pertaining to the development of viable damage evolution equations using a continuum damage mechanics approach are addressed. In particular, limitations associated with the use of ISVs that can be expressed either in terms of macroscopically measurable quantities or through a spatial average of the geometric features of individual damage entities are discussed. Numerical simulations of evolving crack systems in two-dimensional perfectly brittle solids indicate that “effective stress” models may have difficulty in characterizing damage evolution in brittle microcracked solids when the damage consists of cracks of variable size or spatial distributions. An argument for implementing ISVs based on higher-order moments of the damage distribution within an RVE is presented.
A Unified Approach to Metal Fatigue Based on the Theory of Damage Mechanics
Authors: Chow CL , Yu LG
Published: March 2009

This paper presents a unified approach to fatigue damage in metals based on the theory of damage mechanics. The theory that takes into account the gradual material degradation or deterioration under load is ideally suited for characterizing material behaviors progressively damaged under fatigue loading. This is because fatigue damage is caused by material degradation resulting from the initiation, growth, and coalescence of microcracks/voids in real-life materials under repeated/cyclic loading. In addition, a unified fracture criterion based on the damage mechanics theory has been developed to predict the threshold conditions of macrocrack initiation and propagation as well as damage evolution in a material element with or without the presence of a macrocrack. This type of unified approach would not otherwise be possible using the conventional fatigue design methodology based on either the S-N diagram or the concept of fracture mechanics.

The proposed fatigue damage model is based on the thermodynamic theory of irreversible processes with internal state variables. With the introduction of a new damage effect tensor, the necessary constitutive equations of elasticity and plasticity coupled with damage are developed. The constitutive equations derived enable the formulation of a fatigue damage dissipative potential function and a fatigue damage criterion. The criterion is designed to subdivide the overall damage into two domains, namely, “fatigue damage” and “plastic damage.” The fatigue damage evolution equation is subsequently developed based on the hypothesis that the overall damage is induced by the summation of “fatigue” and “plastic” damages. The model has been applied to predict successfully the fatigue life of smooth, notched, and center-cracked specimens under a wide range of loading cycles.
Assessment of a Semielliptical Crack in the Interface Between Ferritic and Austenitic Material on the Basis of the Gurson Model
Authors: Sun DZ , Schmitt W
Published: March 2009

In safety analyses of nuclear reactor pressure vessels, hypothetical cracks are often postulated in the ferritic base material beneath the austenitic cladding that is used to protect against corrosion. The criticality of the hypothetical cracks is strongly influenced by the integrity of the cladding. If the cladding is intact, the crack tip loading is significantly reduced compared with the case where the cladding is assumed to be broken. The assessment of the load-carrying capacity of such a cladding cannot be done on the basis of the J-integral concept since its application is problematic at the interface of two materials and steep gradients in the material properties in the heat-affected zone cannot be characterized by fracture mechanics tests meaningfully. Moreover, the shape of cracks is usually assumed as semielliptical and the conventional J-concept has to be modified to take into account the effect of the constraint, changing along the crack front, on the crack resistance behavior. To avoid these problems, the behavior of a flaw in the interface between ferritic and austenitic material has been analyzed by a micromechanical material model based on the Gurson flow function.

A three-point-bend specimen consisting of a ferritic block with an austenitic cladding and a semielliptical crack in the ferritic base material beneath the cladding was tested and evaluated. The global (that is, load versus displacement curve) and local (that is, ductile crack extension in ferrite and austenite) behaviors of this specimen were predicted by means of two- and three-dimensional finite element analyses with the Gurson parameters determined for different material zones. The material characterization was done by utilizing subsized tension tests with improved evaluation and fracture mechanics tests with precracked Charpy-type specimens.
Stress History Dependent Localization and Failure Using Continuum Damage Mechanics Concepts
Authors: Horstemeyer MF , Revelli V
Published: March 2009

Since the notion of damage was introduced by Kachanov and Rabatnov in the late 1950s and early 1960s, the paradigm to better capture the physics of the internal state of a material has been realized in developing macroscale constitutive relationships for monolithic and composite materials. For ductile metals, damage occurs mainly in the form of void nucleation, growth, and coalescence. Localization and failure occur at two different stages in the deformation history and are very much functions of the void (porosity) evolution, which can be interpreted as the damage evolution, and the stress state history. The damage evolution of a polycrystalline metal is fully coupled to the stress history. In this study, different initial material properties are varied in four different boundary value problems to reflect the stress state and deformation history effects. Special attention is paid to three internal state variable evolution equations; one represents scalar damage, and the other two represent isotropic (scalar) hardening and kinematic (tensorial) hardening. Internal state evolution equations that capture history effects are necessary when trying to solve complex boundary value problems. This constitutive framework is embedded into a finite element formulation to solve such boundary value problems. Mesoscale analyses of A356- T6 aluminum under different stress states and initial material states are used to give insight into the void nucleation, growth, and coalescence issues that arise when formulating an internal state porosity evolution rule within a macroscale framework. This work was based on previous studiesrelated to the four boundary value problems. Numerical calculations were performed to compare to 6061-T6 aluminum notch tension tests with different notched radii. The various notch radii induce different levels of stress triaxiality and allow for correlation of different void growth rules. Numerical calculations of forming limit diagrams for 6061-T6 aluminum compared favorably to experimental results. Finally, penetration analyses were performed with 6061-T6 aluminum disks as targets.
An Advanced Multiple Frequency ACPD System for Crack Detection and Calibration
Authors: Tiku S , Marchand NJ , Unvala B
Published: March 2009

On-line crack detection and crack depth measurements have been carried out using a novel sensor. The sensor is based on an advanced alternating current potential difference (ACPD) technique. This sensor makes use of a new technology called current focusing (CF) which allows the current distribution on the surface to be selectively confined to a precise region (e.g., in a high stress gradient domain). The use of AC currents in conjunction with the current focusing technique results in having a three — dimensional control of the current density distribution in a solid. As a result, the technique can be used on large structures as well as on standard specimens. The associated advanced electronics, having variable frequency capabilities (500 Hz to 240 kHz) and variable currents up to 5 Amperes has been designed and will be briefly described. To assess the performance of the system and ACPD/CF technologies, a fatigue testing program was carried out on single edge notch specimens made of Al 7075 alloys. Naturally initiated fatigue cracks in the range of 200 μm to 6mm have been detected. Potential difference versus crack depth calibrations curves were obtained for various combinations of currents and frequencies with a reliability better than 99%. Furthermore, off-line measurements have been carried out to assess the applicability of the technique for NDI applications.
BISMAP: A Non-Contact Biaxial Displacement Measurement System
Authors: McKeighan PC , Seida SB , Franke EA , Davidson DL
Published: March 2009

The development and validation of a prototype BISMAP (Biaxial Displacement Measurement by Machine Vision Processing) system is described. The non-contact biaxial displacement measurement system adapts machine vision technology to create a unique extensometer. The BISMAP system is built around a vision processing system that tracks and recognizes surface texture features around specific control points by using a normalized correlation technique. The system has numerous advantageous features including non-contact measurement in two-dimensions, variable gage length, direct surface measurement (no attached target) and real-time measurement of multiple, discrete points. The performance of the system is demonstrated with evaluations of the monotonic (and in some cases cyclic) stress-strain response for four different materials: aluminum, LEXAN, rubber and baboon tendon. The system has a measured accuracy of 370 μϵ with ±50 μϵ variability when compared to a strain gage. It is best-suited for measuring strains in excess of 5000 μϵ and there is no practical upper limit on the measurable strain with retraining. The BISMAP system shows promise for development from prototype into a laboratory instrument capable of measuring strains in pliable or delicate materials.
A Review of Strain Measurement Techniques Using the Grid Method
Authors: Cárdenas-García JF , Wu MM , Hashemi J
Published: March 2009

The grid method is the oldest and simplest method for strain measurement. It is an experimental technique in which a grid is applied to the surface of a specimen. A grid is defined as one or more lines, dots or other shapes assembled in regular or irregular patterns. A comparison of the deformed grid on the specimen, undergoing a general state of loading, to that of a reference state yields the state of deformation. The emphasis in this paper is on reviewing experimental techniques emphasizing optical, non-contact, non-interfering and automated means of making deformation measurements using the grid method. Thus, the objectives of this paper are: to briefly review the basic principles and applications of the grid method in transparent and opaque solids, to describe the state-of-the-art, and, to point in the direction of its future evolution.
New Developments in Full Field Strain Measurements Using Speckles
Authors: Chiang F-P , Wang Q , Lehman F
Published: March 2009

Speckle photography is a versatile full field technique for measuring displacement and strain. However, the wet photographic process and tedium of fringe analysis had made it impractical for application to industrial problems. This paper describes a recent development of combining digital recording and image analysis that has rendered the technique a practical tool. In addition, through the development of SIEM (Speckle Interferometry with Electron Microscopy) the technique has been extended into micromechanics domain whereby strain fields within a region only a few micron square can be mapped with confidence. Several examples of this application are presented.
An Array Measurement System for Thermoelastic Stress Analysis
Authors: Welch CS , Cramer KE , Lesniak JR , Boyce BR
Published: March 2009

Thermoelastic Stress Analysis (TSA) is defined, and an overview is given to show its potentially wide applicability and brief history. A simplified calculation of instrumental response characteristics shows the substantial improvement in data acquisition speed that can be gained in a system using a staring array in comparison to that using a scanned detector. Descriptions are given of several methods which have been used to obtain data for thermoelastic stress analysis. Finally, image representations are presented of TSA data taken with a staring array imager showing the resolution attainable in practice using some laboratory fatigue samples and a prototype part.
Thermoelastic Stress Analysis of the Human Tibia
Authors: Hyodo K , Yamada M , Tateishi T
Published: March 2009

The thermoelastic stress analysis method is a non-contact technique which utilizes the thermoelastic qualities of hard tissues such as bones. It enables easy measurement and imaging of surface stress distributions. Using this approach, we performed stress analyses of human tibias in simulated loading conditions at various modes of varus valgus loading on the knee joint. In normal loading, the greatest stress image was obtained on the posterior aspect, indicating that the majority of the stress was concentrated in the posterior part of the tibia. The epiphysis of the proximal tibia, which consists predominantly of cancellous bone, showed tensile stress and the diaphysis which consists of compact bone showed compressive stress in every plane. These results indicate that the tensile stress in the epiphyseal surface indirectly reflects the impact-absorbing properties of cancellous bone. Also, results demonstrated that small changes in the alignment of the knee joint have a great influence on the stress pattern of the proximal tibia.
Process-Induced Effects in Compression Molding of Ultra-High Molecular Weight Polyethylene (UHMWPE)
Authors: Ramani K , Parasnis NC
Published: March 2009

Manufacturing of high quality compression-molded parts requires a thorough understanding of the effect of processing conditions on the quality of the final part. The effect of eight different processing variables on the quality of compression-molded patella buttons was investigated using a design of experiments approach based on Taguchi methods. The quality of the patella buttons was characterized using density, crystallinity, tensile strength, tensile modulus, and optical microscopy for microstructure. Tension testing was carried out on microtomed films and was found to be sensitive to the consolidation of the powder. The tension testing was used to reveal the effect of processing on tensile modulus and tensile strength. Density was affected the least by the variations in processing conditions, crystallinity and Young's modulus were moderately affected, while tensile yield strength was affected the most. Among the different processing variables, soak time at melt, cooling rate from melt, and the pressure applied during the processing cycle caused the maximum changes in the crystallinity, strength, and stiffness of the part. The presence of incompletely fused flakes in the poorly consolidated parts led to a viscous behavior of films with a low crystallinity and modulus. However, well-consolidated parts had a high crystallinity and modulus.
Viscoelastic Recovery of Creep-Deformed Ultra-High Molecular Weight Polyethylene (UHMWPE)
Authors: Lee K-Y , Pienkowski D
Published: March 2009

Viscoelastic creep recovery of ultra-high molecular weight polyethylene (UHMWPE) was quantified as a function of time and applied pressure for both static and dynamic loading. Unirradiated extruded GUR 4150HP UHMWPE specimens were compressed by using static and dynamic (1-Hz sinusoidal) loads with clinically relevant (hip) peak pressures of 2, 4, and 8 MPa in 37°C bovine serum for 10 000 minutes. Thereafter, loads were removed and the thicknesses of the specimens were measured periodically in air for up to 10 000 minutes.

The creep strains recovered as a function of log time for all pressures in both static and dynamic loading. Regardless of load amplitude, load type, and radial location from which the specimens were machined from the extruded rod stock, approximately 51 % of the total creep deformation was ultimately recovered, and 73% of the recovered creep strain occurred during the first 1000 min after unloading. These data emphasize the need to account for the amount of creep recovery when estimating wear rates with in vivo radiographic penetration measurements and the dimensions of retrieved implants.
A New Method to Determine the Locus of Radiation Damage in Retrieved Ultra-High Molecular Weight Polyethylene (UHMWPE) Components
Authors: Muratoğlu OK , Imlach H , Jasty M , Harris WH
Published: March 2009

Gamma-sterilization can damage ultra-high molecular weight polyethylene (UHMWPE) that, after three to five years or more, can lead to the embrittlement of the polymer. In many cases, thin cross sections (100 μm) of the polymer have a gross appearance of a “white band,” generally 1 to 2 mm below the surface. This white band consists of cracks induced during sectioning in areas of embrittlement. We studied oxidation changes resulting in chain scission by exploring the effects of hot (110°C) xylene extraction on aged UHMWPE acetabular components. Hot xylene is a good solvent for polyethylenes and extracts the lower molecular weight species from UHMWPE. In so doing, it also extracts the lower molecular weight species that result from chain scission.

The xylene extraction studies revealed two interesting observations. First, the extent of extraction-induced white band was substantially in excess of the sectioning-induced white banding. The infrared determination of the oxidation extent was more accurately indicated by extraction than sectioning. Secondly, microscopic observation of the material prior to and after xylene extraction showed that the regions of greatest extraction of polyethylene were at the interfaces between individual flakes of the starting material. This observation indicates that a major site of preferential removal of polyethylene was at the interfaces and supports the concept of preferential O2 diffusion along the boundaries between the flakes of the original polyethylene resin.
A Review of the Use of Modularity in Total Shoulder Arthroplasty
Authors: Zuckerman JD , Cavallo RJ , Kummer FJ
Published: March 2009

Modularity is a recent advance in total shoulder arthroplasty (TSA). The use of a separate head-stem combination permits intraoperative adjustment of soft tissue tension necessary for successful TSA. Modular glenoid components allow auxiliary fixation by various coatings or screws. Short-term clinical results (<5 years) indicate that the results of modular TSA are equivalent to those of monolithic TSA. Several cases of headstem disassociation have been observed. It is possible that taper corrosion and polyethylene insert failure could occur in the long term, as has been seen with modular hip replacement.
The Fibrous Tissue Interface Surrounding Well-Fixed, Revised, Cementless Acetabular Components for Hip Replacement
Authors: Goodman SB , Huie P , Song Y , O'Connor M , Woolson ST , Maloney WJ , Schurman DJ , Sibley R
Published: March 2009

Ten well-fixed, cementless, metal-backed acetabular components were revised due to recurrent hip dislocation, polyethylene wear or during femoral revision due to aseptic loosening. Eight cups were modular and two cups were nonmodular. Seven of the eight modular cups were fixed with one or more screws; the two nonmodular cups had two pegs but no screws for fixation. The cups were revised after a period of 3.5–72 months. The fibrous tissue surrounding the implant was harvested, and frozen sections were processed using immunohistochemistry and in situ hybridization. The tissue formed a thin, gritty, incomplete fibrous layer that was tightly adherent to the surface of the metal-backed components. Scattered macrophages and lymphocytes were present within the fibrous stroma in all tissues. Gross, black metallic staining of 3 tissues was associated with increased cellularity. Generally, macrophages expressed mRNA for EL-1, IL-6, PDGFa, and TNFa, and fibroblasts were TGFb positive; these factors are known to modulate the remodeling of bone. No relationship was found between the cellular and cytokine profiles and modularity, the type of metal backing, the presence of screws or the time in situ. The fibrous tissue surrounding well-fixed, cementless, metal-backed acetabular cups undergoing revision surgery contained many of the cellular elements and cytokines associated with loosening and osteolysis.
Effects of Neck Extension, Coverage, and Frequency on The Fretting Corrosion Of Modular THR Bore and Cone Interface
Authors: Brown SA , Abera A , D'Onofrio M , Flemming C
Published: March 2009

Examination of retrieved modular total hip replacements (THR's) has identified fretting corrosion as one of the principal mechanisms of implant corrosion at the bore and cone interface. Increased instability due to increased neck extension has been attributed to one of the design factors affecting corrosion rates. A series of experiments was conducted on THR's with cobalt chromium molybdenum alloy heads and Ti 6Al 4V stems, which demonstrated higher fretting corrosion currents with longer neck extensions. Shortening the skirt reduced corrosion rates. In a second series, the effects of wave form and cycling frequency demonstrated higher currents with a ramp versus a sine wave, and higher currents with higher frequencies. Examination of the frequency components of the Paul curve for loads on the hip during gait demonstrated that higher frequencies may be appropriate for device testing.
Ultrasonic Measurement of the Regression Rate of the Melting Interface in Burning Metal Rods
Authors: Steinberg TA , Veidt M
Published: March 2009

Results of tests in which metallic rods are burned in oxygen-enriched atmospheres often include the regression rate of the melting interface for the burning test specimen. This regression rate is used as an indication of a metallic materials' relative flammability when different metallic materials burn at the same test pressure and as an indication of a metallic materials' general ability to sustain burning under the test conditions. Most past methods for determining this regression rate have been based on visual interrogation which is costly, time consuming and often inaccurate. Inaccuracies typically result due to the specific method used (scale factors, optics, visualisation techniques, etc.), and often a limited access time with which to view the combustion event, or obscuration of the burning by condensed-phase products. An ultrasonic transducer has been fabricated to directly measure the regression rate of the melting interface established during the burning of metal rods, thus eliminating many of these problems. The transducer is described, typical results for an iron rod burning in pure oxygen are given along with a comparison of these results with regression rates obtained from visual interrogation. Excellent agreement is obtained between the regression rate obtained from the new ultrasonic transducer and regression rates obtained visually, thus demonstrating the transducer's usefulness.
Promoted Ignition-Combustion Behavior of Alternative High Performance Engineering Alloys in Oxygen-Enriched Atmospheres
Authors: McIlroy K , Zawierucha R , Million JF
Published: March 2009

Promoted ignition and more recently promoted combustion are terms which have been used to describe a situation where a substance with low oxygen compatibility ignites and supports the combustion of a more combustion resistant material. Previous work has been reported on the investigation of this phenomenon as it relates to carbon steel, stainless steels and a number of significant engineering alloys in the nickel, cobalt and copper families.

Alloys which were tested in this investigation included: AL-6XN stainless steel, 347 stainless steel, INCO A weld filler metal, HAYNES HR-160, HAYNES 214, HAYNES 230, HAYNES 556 and HAYNES ULTIMET.

These alloys represent a substantial range of alloy composition, capability and cost. Potential service environments include hazardous waste, marine, heavy industrial, electronics and various elevated temperature applications where oxygen enriched environments may be encountered.