bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the Influence of Low Density Polyethylene Modification (Novophalt) of Asphalt Concrete on Mixture Shear Strength and Creep Deformation Potential
Authors: Little DN
Published: March 2009

Low density polyethylene (LDPE) when dispersed in asphalt cement through a high shear blending process produces asphalt concrete mixtures (Novophalt) with superior resistance to deformation at high service temperatures. The dispersion of LDPE within the asphalt results in rheological changes in the binder which not only significantly improve resistance to creep deformation but also improve mixture shear strength. The ratio of induced octahedral shear stress in a paving mixture to the octahedral shear strength of the paving mixture at the specific conditions of loading is used to demonstrate the ability of Novophalt to reduce deformation potential of asphalt pavements through improved shear strength. The results of the shear strength analysis are corroborated by creep deformation and accumulated permanent strain analyses.
The Determination of Bitumen and Recycled Tire Rubber Content on Rubberized Asphalt Road Mixtures
Authors: Ista EJ , Choquet FS
Published: March 2009

The improvement of road user comfort associated with environmental protection by waste disposal has been incentive to the modification of bituminous binders by incorporating powdered rubber recovered from used tires. The adhesive properties of rubber-bitumen binders make it possible to construct porous asphalt surfacings the advantages of which lie in easy drainage of surface water, resistance to skidding, flexibility at low temperatures, and reduced noise levels. The construction of such surfacings involves the introduction of powdered rubber into the bitumen, in a known proportion which must be controlled. It is also important to be able to determine the binder content of such mixtures while allowing for the presence of rubber. The procedure for the cold extraction of the bitumen and the separation of the insoluble constituents by centrifugation is modified to enable powdered rubber to be distinguished from aggregates. This separation is obtained by suspending the rubber in trichloroethylene and then filtrating.
Thermo-Oxidative Degradation of Polymer Modified Bitumen
Authors: Linde S , Johansson U
Published: March 2009

Mixtures of the styrene-butadiene-styrene (SBS) and styrene-ethylene-butene-styrene (SEBS) respectivly with different types of bituminous materials or oils have been investigated. We can here, with the aid of size exclusion chromotography (SEC), suggest that pronounced molecular size changes occur both in the bitumen and the polymer phase due to processing and ageing. The processing temperature was chosen to 200 °C (392 F) and the ageing temperature to 70 °C (158 F). The changes in molecular size are correlated to changes in mechanical properties. Compatibility conditions also seem to influence the degradation course. Prolonged exposure of the materials to 200 °C in inert, nitrogen, atmosphere has also been performed. No detectable difference in molecular weight could be found. The results give important implications for both processing handling and long term properties of modified bitumen.
Characterisation of Polymer Modified Asphalt Binders for Roads and Airfields
Authors: Jain PK , Bose SS , Arya IR
Published: March 2009

This paper elaborates on the characterisation of styrene butadiene styrene, ethyl vinyl acetate, low density polyethylene, polypropylene wax and hydroxylterminated polybutadiene modified asphalts by penetration temperature sensitivity, thermogravimetric analysis, penetration ratio, cohesion, adhesion, stability, tensile strength and flexural fatigue test. The benefits obtained by the modification of asphalt with polymers are improvement in quality of asphalt as defined by increased cohesion, adhesion, elastic recovery and reduced temperature sensitivity. The significant characteristics of polymer modified asphalts are high stability, tensile strength, stiffness and extended fatigue life. The effects of wax in waxy asphalts is reduced by incorporation of polymers.
HPLC Analysis for Epoxy Coatings Resins
Authors: Sheih DP , Benton DE
Published: March 2009

A review of the recent progress in development of HPLC techniques for the analysis of epoxy resins is presented in this paper. Three categories of epoxy resins, i.e., liquid, solid, and novolac epoxy resins, are included in the discussion. For analyzing oligomers and other components of these resins, HPLC has been recognized as the best choice based on speed, reliability, and accuracy of analysis. Successful resolutions of major components in the epoxy resins have been reported based on using reversed phase HPLC, UV detection, and acetonitrile/water or tetrahydrofuran/water solvent mixes and gradient elution techniques. Different components of the epoxy resins can be responsible for the success or failure in the performance of a coating formulation. Examples are given of some component identifications and their possible relationships to epoxy coatings properties, such as adhesion, viscosity, and flexibility.
X-Ray Techniques for Coatings Analysis
Authors: Snider AM
Published: March 2009

X-ray diffraction (XRD) and X-ray fluorescence spectrometry (XRFS) are powerful, well-established tools used by analytical chemists in many areas of technology. However, their potential in the coatings industry has not been fully exploited. XRD is convenient for the identification of diverse crystalline solids encountered in paint research laboratories and production plants. It is particularly well suited for use in the identification and quantitative analysis of crystalline pigments and extenders, either alone or when present in pastes or paint. XRFS is useful as a stand-alone technique for elemental analysis and as a complementary tool for use with other analytical techniques. X-ray spectrometers typically can analyze all elements with an atomic number of about 11 and higher, but some units can reach as low as atomic number 5. XRFS spans the concentration range from parts per million to high percentages for most elements in liquid or solid samples. Dedicated XRFS units, much lower in cost than scanning spectrometers, can be set up to detect and quantify one or a few specific elements. Portable XRFS units are available for field investigations. A survey of the principles, applications, and limitations of XRD and XRFS is given.
Chemical Characterization of Cross-Linked Polyurethane Films
Authors: van der Ven LGJ , van Houwelingen GDB , Lamping RR
Published: March 2009

The chemical composition and the physical properties of two-component polyurethane coatings are influenced by the curing conditions, viz. relative humidity and temperature. Apart from the formation of urethane, carbon dioxide can be released by hydrolysis of the isocyanate groups, leading to the formation of urea groups.

Chemical-analytical methods have been developed to characterize cross-linked polyurethane coatings based on hydroxy-functional acrylic resins and trifunctional isocyanates. Spectroscopic and wet chemical methods as well as carbon dioxide measurements were applied. Quantitative data were obtained on the content of isocyanate, hydroxyl, and amino groups and on urethane and urea cross-links.

The influence of the curing temperature, relative humidity, and type of hydroxyl groups on the network structure has been investigated. The relative humidity influences the composition of the coating cured at ambient temperature. During curing at elevated temperatures, the relative humidity hardly affects the chemical structure of the film. However, during storage after baking, urea groups are formed.
Principles and Applications of Photoelectron and Ion Spectroscopy for the Analysis of Polymer Surfaces
Authors: Gardella JA
Published: March 2009

Advances in the development of techniques for the energy and mass analysis of ejected particles, form the basis of their use as surface analytical spectroscopies. Methods such as X-ray photoelectron spectroscopy (XPS or ESCA), low-energy ion-scattering spectroscopy (ISS), and secondary ion mass spectrometry (SIMS) are becoming more widely applicable to problems in the chemical analysis of coatings surfaces and interfaces. In this paper a brief review of instrumentation and theory allows projection of new capabilities for the method. Recent progress in the analysis of homopolymer and multicomponent polymer interfaces is described.
Failure Analysis of Applied Coatings
Authors: Tator KB , Weldon DG
Published: March 2009

When protective coatings are properly formulated and applied, they are usually expected to last ten years or more with periodic maintenance. However, occasionally, premature failure occurs, with expensive cost ramifications. The investigation of a field coating failure is considerably different than routine paint analysis, even though the same laboratory equipment is used. Instead, a forensic analysis technique is required, which relies heavily on background information, field sampling and observations, and laboratory testing and analysis.

This paper will describe how one coating consulting company conducts the field and laboratory investigation of coating failures. The structure of failure analysis will be illustrated by three different failures. The first failure involves an alkyd applied over concrete; the second failure involves the delamination of a urethane topcoat from an epoxy primer; and the third failure involves the cohesive failure of an inorganic zinc-rich primer topcoated with a vinyl system.
A Framework for Quantifying Crack Tip Constraint
Authors: Shih CF , O'Dowd NP , Kirk MT
Published: March 2009

The terms high and low constraint have been loosely used to distinguish different levels of near tip stress triaxiality in different crack geometries. In this paper, a precise measure of crack tip constraint is provided through a stress triaxiality parameter Q. It is shown that the J-integral and Q are sufficient to characterize the full range of near-tip fracture states. Within this framework J and Q have distinct roles: J sets the size scale over which large stresses and strains develop, while Q scales the near-tip stress distribution relative to a reference high triaxiality state. Specifically, negative (positive) Q values mean that the hydrostatic stress ahead of the crack is reduced (increased) by Qσ0 from the plane strain reference distribution.

The evolution of near-tip constraint as plastic flow progresses from small-scale yielding to fully yielded conditions is examined. It is shown that the Q parameter adequately characterizes the full range of near-tip constraint states in several crack geometries. Through-thickness deformation and stress conditions affect near-tip triaxiality. Stress triaxiality near a three-dimensional crack front is measured by pointwise values of Q.

The J-Q theory provides a framework that allows the toughness locus to be measured and utilized in engineering applications. A method for evaluating Q in fully yielded crack geometries and a scheme to interpolate for Q over the entire range of yielding are presented. Extension of the J-Q theory to creep crack growth is discussed in the concluding section.
Constraint and Toughness Parameterized by T
Authors: Hancock JW , Reuter WG , Parks DM
Published: March 2009

A series of cracked specimen configurations have been tested to correlate the geometry dependence of crack tip constraint and fracture toughness in full plasticity. Specimens with through cracks included a range of edge-cracked bend bars, compact tension specimens, and center-cracked panels. Surface-cracked panels were tested in tension to produce resistance curves.

The geometry dependence of ductile crack extension in plane strain has been correlated with crack tip constraint as parameterized by the T stress, which indicates the nature of the development of higher order terms in the nonlinear asymptotic crack tip expansion.
Influence of Crack Depth on the Fracture Toughness of Reactor Pressure Vessel Steel
Authors: Theiss TJ , Bryson JW
Published: March 2009

The Heavy Section Steel Technology Program (HSST) at Oak Ridge National Laboratory (ORNL) is investigating the influence of flaw depth on the fracture toughness of reactor pressure vessel (RPV) steel. Recently, it has been shown that, in notched beam testing, shallow cracks tend to exhibit an elevated toughness as a result of a loss of constraint at the crack tip. The loss of constraint takes place when interaction occurs between the elastic-plastic crack-tip stress field and the specimen surface nearest the crack tip. An increased shallow-crack fracture toughness is of interest to the nuclear industry because probabilistic fracture-mechanics evaluations show that shallow flaws play a dominant role in the probability of vessel failure during postulated pressurized-thermal-shock (PTS) events.

Tests have been performed on beam specimens loaded in three-point bending using unirradiated RPV material (A533 B). Testing has been conducted using specimens with a constant beam depth (W = 94 mm) and within the lower-transition region of the toughness curve for A533 B. Primarily two crack depths have been considered: a = 50 and 9 mm (a/W = 0.5 and 0.1). Three specimen thicknesses (B = 50, 100, and 150 mm) have been used to examine the influence of different out-of-plane constraint conditions on the test results. All tests resulted in cleavage failures. Test results indicate a significantly higher fracture toughness associated with the shallow flaw specimens compared to the fracture toughness determined using deep-crack (a/W = 0.5) specimens. The toughness increase is comparable with the toughness increase found at the University of Kansas using steels whose stress-strain properties bound those of A533 B. Test data also show little influence of thickness on the fracture toughness for the current test temperature (-60°C). The Irwin βc correction has been modified to account for shallow flaws and was used to estimate the shallow-flaw toughness based on the results from the deep-crack specimens.
On the Two-Parameter Characterization of Elastic-Plastic Crack-Front Fields in Surface-Cracked Plates
Authors: Wang Y-Y
Published: March 2009

Plane-strain elastic-plastic crack-tip fields at a constant J and various elastic T-stress levels were obtained in a modified boundary layer (MBL) formulation similar to that of Betegón and Hancock but with a slightly different power law hardening stress-strain law. The analyses were based upon small geometry change formulation and deformation theory plasticity. To verify the two-parameter characterization of elastic-plastic crack-tip fields, three-dimensional (3-D) elastic-plastic finite element (FE) analyses were performed on plates with deep (a/t = 0.60) and shallow (a/t = 0.15) semielliptical surface cracks under both remote tension and bending. Here t is the plate thickness and a is the maximum penetration of the crack through the plate thickness. In topological planes perpendicular to the semielliptical crack fronts, the crack-opening stress fields, normalized by the local J, were compared with the plane-strain MBL predictions based upon the local J and T. In all four cases studied, better than 94% agreement between the 3-D FE solutions and the plane-strain solutions was obtained for loads up to general yielding. This remarkable agreement held throughout all crack-front locations where the stress fields could be resolved accurately. Given the vastly different distributions of J, T, and crack-opening stress profiles along the collective set of respective crack fronts, the elastic T-stress appears to be a tractable, predictive parameter in quantifying elastic-plastic crack-front stress constraint.
An Experimental Study to Determine the Limits of CTOD Controlled Crack Growth
Authors: Gordon JR , Jones RL , Challenger NV
Published: March 2009

This paper presents the results of an experimental program to study size and geometry effects in CTOD R-curves. The results were obtained from room temperature unloading compliance R-curve tests on different-sized single-edge-notch-bend (SENB) specimens made from Ti-3Al-2.5V alloy, HY100 steel, and nickel-aluminum-bronze (NAB). The crack growth resistance was measured in terms of conventional CTOD, δ0 (i.e., as defined in BS 5762), CTOD corrected for crack growth, δR, and CTOD derived using a double clip gage arrangement, δdc. It was found that all the CTOD R-curves exhibited upswings after crack extensions corresponding to approximately 15% of the initial uncracked ligament. Based on the results obtained in this study, it is postulated that the crack growth limit for CTOD controlled crack growth in R-curves is 15% of the initial uncracked ligament. This condition alone, however, is not sufficient to guarantee size/geometry independent results. It is also necessary to have the same level of specimen constraint.
Specimen Size Effects on J-R Curves for RPV Steels
Authors: Hiser AL
Published: March 2009

This study examined the effect of specimen size on J-R curves for reactor pressure vessel (RPV) steels. Overall comparisons for monolithic materials (base plate and forging) indicated that no significant size effect is apparent, using standard formulations for the J-integral within commonly accepted validity bounds. However, materials that are composite in nature, such as weld materials, or exhibit macro-scale inhomogeneities gave significant differences in JR curve trends for different sizes of specimens.
Effects of Crack Depth and Mode of Loading on theJ-RCurve Behavior of a High-Strength Steel
Authors: Joyce JA , Hackett EM , Roe C
Published: March 2009

This paper describes an experimental program which had the objective of developing a series of J-R curve data from laboratory specimens of varied constraint. Constraint was varied by testing specimens with different thicknesses, crack lengths, and mode of loading. All specimens were relatively small and were kept simple in geometry and loading to allow estimation of the applied J integral. Crack length-to-width ratios were varied dramatically from a/W = 0.10 to a/W = 0.65 and the mode of loading ranges from three-point bending of deeply cracked edge-notched bars to pure tensile loading of double edge-notched strips. All tests were conducted on a single material, a high-strength structural steel, at ambient temperature, which is well up on the ductile upper shelf for this alloy.

Results of these tests have shown that different constraint conditions can dramatically affect the JIc and the J-R curve for the full range of crack lengths and loading modes studied here, and these effects can be studied on relatively inexpensive laboratory specimens. Observed trends correspond to generally expected ideas of “increased constraint” or “decreased constraint” conditions, but since no factor is available to satisfactorily quantify constraint, an ability to utilize a data set such as this to predict the behavior of a material for a particular structural application is still lacking.
Statistical Aspects of Constraint with Emphasis on Testing and Analysis of Laboratory Specimens in the Transition Region
Authors: Wallin K
Published: March 2009

The effect of specimen thickness, side grooving, large-scale yielding of the ligament, and ductile tearing upon the probability of cleavage fracture initiation is examined within the framework of a general statistical model for cleavage fracture initiation. First, a derivation of the statistical model is presented, and then the model is used to explain the effects of different factors affecting the cleavage fracture probability. As a result, a specimen size requirement for elastic-plastic cleavage fracture toughness testing with bend-type specimens is obtained. Additionally, a simple correction function to validate invalid test results with insufficient ligament size and prior ductile tearing is presented.
Thickness Constraint Loss by Delamination and Pop-In Behavior
Authors: Firrao D , Doglione R , Ilia E
Published: March 2009

Fracture toughness of aluminum-lithium 8090-T8 alloy has been investigated. J-R and K-R curves tests have been performed on compact tension (CT) samples machined from a 12-mm-thick plate, both in longitudinal transverse (LT) and transverse longitudinal (TL) directions. Sample thickness and width varied in order to assess the dependence of constraint on the geometry. It was found that, owing to delaminations occurring perpendicular to short transverse direction and local fracture path deviation from Mode I, a relaxation of the degree of thickness constraint inside the material takes place. Large pop-in phenomena ensue, thus hampering the J-R curves interpretation. Metallographic structure and fracture surfaces were investigated to clarify the micromechanisms of fracture and to ascertain the possibility to single out unequivocally the critical event for JIc significant determinations. Also, K-R curves have been explained on the basis of the results of fracture mechanisms and microstructure. The extent to which JIc and K-R curves are representative and size independent, as well as the inapplicability of ASTM Test Method for Plane-Strain Fracture Toughness of Metallic Materials (E 399-83), have been discussed.
Use of Thickness Reduction to Estimate Fracture Toughness
Authors: deWit R , Fields RJ , Irwin GR
Published: March 2009

To help predict the behavior of a nuclear pressure vessel undergoing pressurized thermal shock, values of the arrest toughness are required. The purpose of the work described here is to show how toughness values can be calculated from the thickness reduction (TR) of the tested specimens and then used as “lower-bound” estimates. In the NIST wide-plate crack-arrest test program, 16 single edge-notched tension specimens were fractured, using the 26.7 MN universal testing machine. The first series of tests used HSST A533 Grade B Class 1 quenched and tempered steel, while the second series used a low upper-shelf 21/4 Cr-1 Mo steel. For each specimen the TR was measured on the two halves of the broken specimen and a contour map was constructed. The thickness reduction, TR, along the crack propagation plane can be related to the toughness, K, by the relationship K2 = E ∙ σY ∙ TR, where E is Young's modulus and σY an estimate of the tension effective yield strength adjusted for temperature, strain-rate, and constraint. The results show good agreement with values of K for arrest and reinitiation computed from a finite-element generation-mode analysis. Therefore, the indication of plastic work rate provided by the thickness reduction near the fracture plane is a useful preliminary assessment of the fracture toughness.
Assessing a Material's Susceptibility to Constraint and Thickness Using Compact Tension Specimens
Authors: Smith E , Griesbach TJ
Published: March 2009

If the plastic component JDP of the deformation J integral JD for a nongrowing crack can be related, via a single eta factor, to the plastic work integral, using a single expression that is valid for all deformation levels, both JD and modified J integral JM crack growth resistance curves can be obtained from load, load-point displacement, and crack extension measurements using a single specimen. A theoretical analysis of a simulation model shows that the compact tension specimen, where the deformation is predominantly bending, satisfies this condition; it is not satisfied when there is significant tensile deformation. It is thereby argued that compact tension specimen JM (or JD) resistance curves provide an ideal basis for assessing the susceptibility of a material to thickness-induced constraint effects.
Fatigue Properties of Segmented Polyether Polyurethanes for Cardiovascular Applications
Authors: Hayashi K
Published: March 2009

Effects of temperature (24°, 37°, and 50°C) and cyclic rate (0.8, 2, and 5 Hz) on fatigue behavior were studied on two different segmented polyether polyurethanes immersed in a plasma-analogous cholesterol-lipid solution. Dynamic fatigue tests were carried out under conditions of 50% mean strain and 10% strain amplitude. Changes in the mean stress and the ratio of stress amplitude to strain amplitude were significantly larger at 50°C than at 24° and 37°C. In the initial stage of fatigue testing, changes in these variables appeared earlier at higher cyclic rates. However, the long-term dynamic fatigue behavior was dependent on the duration of testing rather than on the repetition number or the cyclic rate. These results imply that the fatigue testing in the cholesterol-lipid solution of 50°C at the cyclic rate of 5 Hz might be useful for the prediction of long-term behavior of these materials under actual service inside the body.
Predicting the Life and Design Stresses of Medical Plastics Under Creep Conditions
Authors: Teoh SH
Published: March 2009

Polymers are finding increasing use in biomedical engineering applications. One of the major problems in designing with polymers is predicting when the material will fail and what stress values should be used in the design of components in order that the material will not fail prematurely. Recent work on modeling the creep rupture behavior of more than 15 polymers has produced a breakthrough in predicting the failure times as well as the upper stress and lower stress limits of the polymers [1,2]. The upper stress relates to the maximum stress that can be applied to the material before instantaneous fracture. The lower stress limit relates to the minimum stress that can be sustained by the material without failure and, in some cases, this also corresponds to the fatigue endurance limit of the polymer. The creep rupture times of some medical plastics such as high density polyethylene (HOPE), polycarbonate (PC), polypropylene (PP), polyoxymethylene (POM), polyvinylchloride (PVC), polysulphone (PSU), and polymethyl-methacrylate (PMMA) were analyzed at 20°C in air. In order to optimize the parameters for creep rupture prediction, a nonlinear regression analysis program was used [1]. Special attention was made for Delrin (POM from Du Pont) which is of interest in cardiovascular applications related to wear of mechanical heart valves [3] This matenal was tested in air at 37, 60, and 80°C. The effect of saline solution was also studied Here, the lower stress limit was reduced from 20 MPa to 5 MPa. All the specimens brittle fractured This may account why Delrin used in the artificial hip joint prosthesis [4] where the contact stresses exceed this limit was known to wear severely. However, in the disc of the mechanical heart valve [3] no failure occurs because the stresses were probably below the lower stress limit.
Taguchi Experiment on Strength Correlation Between a Customer and Supplier of Porous Coatings
Authors: Peterson RR
Published: March 2009

Problems in correlating porous coating pull-off strength test results through the use of test coupons led to the use of Taguchi methods to isolate the variables that contribute to test result differences between the customer and supplier of these coatings.

In the past, the supplier would test the coupons representative of the parts and ship the parts believing the pull-off strength requirements were met. The customer then tested additional coupons and usually found a lower strength (sometimes below specification) which resulted in rejection of the material. This, of course, led to problems. If both testing sources had correlated at a particular strength level, whether it be high or low, there would be no question as to the disposition of the material. Therefore, the major concern was that the numbers from both testing sources agree.

Since there are scores of variables that could affect the pull-off test, general categories were selected to determine major sources of variation that could be further analyzed at a later date if necessary. The four sources of variation (factors) that were selected included: (1) who performed the gluing operation on the coupons (the supplier or the customer); (2) at which facility the pull-off test was performed (the supplier's or the customer's); (3) what testing fixture configuration was used (two different types); and (4) at what speed was the tensile machine run (two different speeds).

Two analysis methods were used which concluded that the difference in fixturing was probably the most important source of varination While the other factors were significant, it was discovered that the highest pull-off strength values were obtained by having the customer glue the sample and the supplier run the test. This would mean that neither the customer nor the supplier had an overall better technique, further verifying the main source of vanation was in the fixturing.
Identification of The Dynamic Properties of Bone Using The Split-Hopkinson Pressure-Bar Technique
Authors: Tanabe Y , Kobayashi K , Sakamoto M , Hara T , Takahashi H
Published: March 2009

A method has been developed for the identification of the viscoelastic characteristics of compact bone using transient response information obtained from the split-Hopkinson pressure-bar (SHPB) test. The method combines the solution procedures of two problems One is the identification (or inverse) problem and the other is the associated problem, i. e., the prediction (or direct) problem of stress wave propagation in the SHPB. The solutions are accomplished by means of the method of Laplace transformation and Gauss-Newton iterative scheme for nonlinear least squares problems. Numerical experiments are performed to demonstrate the validity of the method established. The method is also applied to the SHPB experiments on bovine femoral compact bone (plexiform bone), assuming that the mechanical behavior of the bone can be represented by the three-element standard linear solid model. The applicability of the model to the bone is also discussed and the orientational dependence of the viscoelastic characteristics of the bone is determined.
Mechanical Evaluation of Soft Tissue and Ligament Implant Fixation Devices
Authors: Stewart NJ , Muneta T , Lewis J , Lindquist C , Arendt E
Published: March 2009

The purpose of this study was to define a new mechanical measure of soft tissue fixation device performance and to use the method to assess the fixation performance of three fixation systems. The commonly used screw and spiked washer (SSW, Synthes) was tested as a method to fix both tendon and Ligament Augmentation Device (LAD, 3M Co.). Also tested was fixation of an LAD with a custom designed ligament implant fixation tab (LIFT). Specimens, goat tendons or LADs, were fixed under 44.5 N of tension to two flat segments of goat bone. Five specimens were tested for each group.

After specimen fixation, increasing loads were applied to the specimen. One bone block was cyclically moved an incrementally increasing distance away from the other, along the axis of the specimen. Between applied loads the bone blocks were returned to their original positions. Two measurements were made at each level of applied load. The first was the force remaining in the specimen with the bone segments in their original positions. The second was the elongation required to return the fixed specimen to its original tension. The second measure was termed slippage, and includes effects of viscoelastic and plastic deformation of the tendon/LAD at both fixation points and within the tendon/LAD. Cyclic loading was continued until failure.

The results are quantified in Table 1. This study demonstrates that soft tissue fixation devices may be characterized by loss of tension, and elongation required to regain original tension, as a function of applied loads. Such information may be useful to evaluate devices that are designed to reduce slippage.
Fiber-Reinforced Polymer Composite Biomaterials: Characterization of Interfacial Bond Strength and Environmental Sensitivity
Authors: Latour RA , Black J
Published: March 2009

Fiber-reinforced polymer (FRP) composite materials are being developed for structural orthopaedic implant applications. The mechanical behavior, particularly the strength, of FRP composites is significantly influenced by fiber/matrix interfacial bond strength. Interfacial bond strength is known to be potentially susceptible to degradation in physiologic environments, and thus is an important area of research for the development of durable FRP composite biomaterials. A relatively simple interfacial bond strength technique has been developed by TRI/ Princeton. We have further implemented and further developed this technique for addressing issues relevant to the development and evaluation of FRP composite biomaterials. In this paper, we present a detailed description of this test technique and outline the methods for sample fabrication, sample testing to determine ultimate and fatigue strength, and data analysis in sufficient detail for others to reproduce this interfacial bond strength and durability measurement technique. Potential test problems leading to erroneous test results and further development areas for this technique are also addressed.
In-Situ SEM Observation of Fatigue Crack Propagation in NT-154 Silicon Nitride
Authors: Salmon DC , Hoeppner DW
Published: March 2009

A miniature 4-kN servohydraulic three-point bend load frame coupled to a scanning electron microscope (SEM) was developed to allow direct observation of fatigue and fracture processes in ceramic materials at magnifications up to X20 000. Two series of fatigue crack growth experiments were conducted on Norton/TRW NT-154 silicon nitride, one using the in-situ three-point bend system and the other using compact tension specimens in a conventional test system. The objectives of the work were to ascertain whether crack growth under cyclic loading is a manifestation of a load-level dependent mechanism or a true cyclic effect, and to identify mechanisms of fatigue crack propagation at a microstructural level. Tests were conducted at room temperature and load ratios of 0.1 to 0.4, both in air and vacuum. Results of both series showed a marked load ratio effect and a distinct cyclic loading effect. Crack propagation was highly discontinuous, occurring on individual cycles at a rate approaching that for fracture and arresting between these growth increments for hundreds or thousands of loading cycles. Between growth increments there were no detectable changes at the crack tip; however, crack wake features such as bridges and interlocking grains decayed and lost their ability to transfer load.
Fatigue Crack Growth Behavior of Surface Cracks in Silicon Nitride
Authors: Mutoh Y , Takahashi M , Kanagawa A
Published: March 2009

Cyclic fatigue crack growth tests of silicon nitride specimens with surface cracks as well as through-the-thickness cracks were carried out. The surface crack length was measured by a surface film gage technique. The fatigue crack growth rate for surface cracks was less than that for through-the-thickness cracks. From SEM observations, more significant bridging was found in the wake of surface cracks compared to through-the-thickness cracks. From evaluations of the stress shielding effect due to bridging based on the measurements of the crack mouth opening displacement, it was found that the crack growth curve determined from the crack tip stress intensity factor Ktip for surface cracks almost coincided with that for through-the-thickness cracks.
Fatigue Response of Metal Matrix Composites
Authors: Schulte K , Trautmann K-H , Leucht R , Minoshima K
Published: March 2009

Results are presented on the fatigue behavior of continuous fiber-reinforced aluminum and titanium alloys, both reinforced with SiC fibers. The pure aluminum matrix was reinforced with the “Tyranno” fiber of Ube, Japan, while the Ti6Al4V matrix was reinforced with the SCS-6 fiber of Textron. Also investigated was an Al-2.5Li alloy reinforced with α-Al2O3 FP fiber from DuPont.

The fatigue behavior of the MMC composites was observed to be superior when compared to the fatigue behavior of bulk matrix material. This was especially true for the case of tension-compression loading, where the overall superior compressive behavior of MMCs played a dominant role.

Failure in an MMC with unidirectional reinforcement normally initiates at or near imperfections, such as misaligned fibers, voids, foreign inclusions, or surface damage with subsequent fatigue crack propagation. An answer is given as to whether the variation of stiffness due to damage development can be used as a damage analogue. Finally, an explanation of the fracture behavior is given.
Fracture Testing and Performance of Beryllium Copper Alloy C17510
Authors: Murray HA , Zatz IJ , Ratka JO
Published: March 2009

When a literature search and discussion with manufacturers revealed that there was virtually no existing data related to the fracture properties and behavior of copper beryllium alloy C17510, a series of test programs was undertaken to ascertain this information for several variations in material processing and chemistry. These variations in C17510 were primarily optimized for combinations of strength and conductivity. While originally intended for use as cyclically loaded high-field, high-strength conductors in fusion energy research, material testing of C17510 has indicated that it is an attractive and economical alternative for a host of other structural, mechanical, and electrical applications.

ASTM tests performed on three variations of C17510 alloys included both J-integral and plane strain fracture toughness testing (E 813, E 399) and fatigue crack growth rate tests (E 647), as well as verifying tensile, hardness, Charpy, and other well-defined mechanical properties. Fracture testing was performed at both room and liquid nitrogen temperatures, which bound the thermal environment anticipated for the fusion components being designed. Fatigue crack propagation stress ratios ranged from nominal zero to minus one at each temperature. In order to confirm the test results, duplicate and independent test programs were awarded to separate facilities with appropriate test experience, whenever possible.

The primary goal of the test program, to determine and bound the fracture toughness and Paris constants for C17510, was accomplished. In addition, a wealth of information was accumulated pertaining to crack growth characteristics, effects of directionality, and potential testing pitfalls. The paper discusses the test program and its findings in detail.
Thermal Fracture and Fatigue of Anodized Aluminum Coatings for Space Applications
Authors: McClung RC , Alwitt RS
Published: March 2009

A concern for the use of anodized aluminum as Space Station thermal control surfaces is the potential degradation of critical optical properties due to oxide coating cracking. This cracking may be induced by differential thermal expansion during hot adhesive bonding of the radiator assembly or during 30 years of exposure to sunlight/darkness cycles in low earth orbit (LEO). This paper summarizes investigations into the effects of temperature and humidity on coating stresses and cracking. Experimentally measured coating residual stresses after anodizing and sealing are shown to be strongly dependent on humidity. Two sets of tests are used to study cracking directly: one determines the temperature (Tc at which cracks first appear during a single heating cycle, while the other involves rapid thermal cycling (RTC) between maximum and minimum temperatures. The effects of several test parameters on cracking are reviewed, with special attention to temperature, coating thickness, and humidity. Fatigue models are developed to describe the observed cracking and to serve as the basis for predictions of LEO cracking. The physical characteristics of cracks and related substrate plastic deformation in both Tc and RTC tests are discussed briefly.
Influence of Fiber-Matrix Interface on Dynamic Response of CFRP
Authors: Elahi M , Reifsnider KL , Swain RE
Published: March 2009

The static and dynamic response of fiber-reinforced composite coupons with various levels of fiber surface treatments was investigated using the classical approach of strain measurement (stiffness degradation using an extensometer), as well as a dynamic phase and dynamic gain (dynamic compliance) response measurement method proposed by Elahi et al. [1]. From the experimental results, the property data are shown to correlate with the classical method of damage monitoring and demonstrate the advantages of the phase and gain response analysis. The proposed approach makes it possible to monitor continuously the fatigue damage evolution in any material system in real time without the use of an extensometer or strain gages, making it an ideal candidate for studying damage under high temperature or extremely corrosive environments where the usage of extensometers is either not practical or not possible.
The Evaluation of Fatigue Damage in Short Fiber-Reinforced Styrene-Maleic Anhydride
Authors: Hoppel CPR , Pangborn RN
Published: March 2009

The fatigue behavior of short glass fiber-reinforced styrene-maleic anhydride (S/MA) is investigated in this study. Six material configurations were manufactured into tensile bars by injection molding and tested in tension-tension (R = 0.1) fatigue to evaluate the ways the interface controls the change in the mechanical properties of the composite. These materials included unreinforced S/MA as a reference material and composites incorporating fiber reinforcement with different average diameters, two volume fractions, the presence or absence of an interfacial silane coupling agent, and fibers prepared with an acrylonitrile/butadiene latex coating. These materials have been tested under both “wet” (immersed in water at 25°C) and “dry” (50% relative humidity at 25°C) conditions. Three indicators were monitored during fatigue to evaluate the damage in the experimental materials: the degradation of the secant and fatigue moduli, the hysteresis energy per cycle, and the concurrent acoustic emissions produced during fatigue. This information is presented with S-N curves to show the relationship between these indicators and the fatigue lives of the materials.

The fatigue performance (life curves and cyclic stress-strain curves) was directly related to the fiber-matrix interface. Since water weakens the interface, especially in the composites without a silane coupling agent, composites tested in the aqueous environment exhibited shorter fatigue lives than the specimens tested in the dry environment. Interfacial coatings that included a silane couplant were found to reduce the effects of water on the fatigue lives of the composites. This damage in the composites was reflected in the decrease in the elastic modulus and the increases in the hysteresis energy and acoustic emissions. These evaluation techniques show that fatigue damage accumulates in a three-stage process in the material.
Characterization of Adhesively Bonded Joints by Acousto-Ultrasonic Techniques and Acoustic Emission
Authors: Nayeb-Hashemi H , Rossettos JN
Published: March 2009

Reliable applications of adhesively bonded joints require an effective nondestructive evaluation technique for their bond strength prediction. To properly evaluate factors affecting bond strength, effects of defects such as voids and disbonds on stress distribution in the overlap region must be understood. At the same time, in order to use the acousto-ultrasonic technique to evaluate bond quality, the effect of these defects on the dynamic response of single lap joints must be clear.

The Stress distribution in a single lap joint with and without defects (void or disbond) is analyzed. A θ parameter that contains adherend and adhesive thickness and properties is introduced. It is shown for bonded joints with θ ≥ 10 that a symmetric void or disbond in the middle of overlap up to 70% of overlap length has a negligible effect on bond strength. In contrast, frequency response analyses by a finite element technique showed that dynamic response is affected significantly by the presence of voids or disbonds. These results have direct implication in the interpretation of acousto-ultrasonic results.

Through-transmission attenuation and a number of acousto-ultrasonic parameters for various specimens with and without defects are evaluated. It is found that, although void and disbond have similar effects on bond strength (stress distribution), they have completely different effects on wave propagation characteristics. For steel-adhesive-steel specimens with voids, attenuation changes are related to the bond strength. However, the attenuation changes for specimens with disbond are fairly constant over a disbond range. In order to incorporate the location of defects in acousto-ultrasonic parameters, a weighting function is introduced. Using an immersion system with focused transducers, a number of acousto-ultrasonic parameters are evaluated. It is found that, by incorporating weighting functions in these parameters, better sensitivities (acousto-ultrasonic parameters versus bond strength) are achieved.

Acoustic emission activities of steel-adhesive-steel specimens with θ = 3.4 are monitored. Two different formats of energy versus time have resulted, each corresponding to the perfect specimens or the specimens with void or disbond. The relative acoustic energy and number of events at failure are found to be a means of predicting bond strength.
SHRP's Layer Moduli Backcalculation Procedure
Authors: Rada GR , Richter CA , Jordahl P
Published: March 2009

Deflection basin measurements for the purpose of structural capacity evaluation are a key component of the SHRP's LTPP monitoring program. In the near term, SHRP will apply a backcalculation procedure to these data in order to estimate the in situ elastic moduli of the pavement layer materials. Because a standard method for evaluating the structural capacity of pavements from deflection data does not presently exist, SHRP has undertaken a study to develop a layer moduli backcalculation procedure for use in the initial analysis of the SHRP deflection data. The procedure covers not only the software but also the rules and guidelines used in applying the program. This paper focuses on the standard procedure used to ensure that the LTPP deflection data analysis is as consistent, productive, and straightforward as possible.
Verification of Pavement Responce Models
Authors: Ullidtz P , Krarup J , Wahlman T
Published: March 2009

When backcalculating layer moduli from Falling Weight Deflectometer (FWD) tests and when forward calculating critical stresses and strains, a number of assumptions have to be made. Some of the important assumptions normally are that 1) the system is in equilibrium, 2) the materials are continuous and remain continuous under deformation, and 3) the materials are elastic, isotropic and homogeneous.

None of these assumptions are valid for FWD testing of real pavement structures. A number of mathematical models exist for describing the pavement response, but they are all based on idealization of real pavement structures and materials. The only way of determining whether a given mathematical model is acceptable for pavement design or evaluation, is by comparing the response predicted by the model to that measured in real pavements.

Many attempts at doing this have been done over the years, but none of them have let to the conclusive verification of a specific mathematical model. This paper presents the results of measurements carried out on four instrumented test sections, one in the Danish Road Testing Machine and three on experimental sections in Sweden. On all sections the deflections were measured with a FWD, the layer moduli were backcalculated using different methods, and the stresses and strains in different materials, caused by FWD loading or by traffic loading, were calculated and compared to the stresses and strains measured at the same locations with pressure and strain gauges.