bluuebunny/crossref_metadata_2025 huggingface dataset:
SBS Polymer Modified Asphalt Binder and its Implications on Overlay Design
Authors: Srivastava A , Hopman PC , Molenaar AAA
Published: March 2009

Substantially improved overlay mixes, required by the modern road industry should be highly resistent to reflection cracking. The mix must contribute significantly to the stiffness of the pavement, even when it is applied in relatively thin layers. The binder should possess a high softening temperature to reduce the sensitivity for rutting and corrugation, and it should have a reasonable penetration value to minimize the chances of cracking. In this paper attention is paid to the manner SBS polymer modified asphalt binders cope with this set of requirements. The basic principles of this modification are outlined and emphasis is laid on the rheological and mechanical properties: viscosity and penetration test results are presented. Burgers' model for viscoelastic materials is used in an attempt to describe the visco elasticy. Results of indirect tensile tests are reported, including the tensile strengths and the elastic moduli. Repeated loading tests have been done on polymer modified and plain asphaltic concrete mixes. The results are mutually compared concerning fatigue behaviour, elastic moduli and crack propagation characteristics. The paper describes various trial sections, with special attention to comparative tests carried out in an Australian accelerated loading facility.
Modern Analytical Techniques for Coating and Coating Materials
Authors: Schernau U , Hueser B , Weber K
Published: March 2009

The past decade has been characterized by an evolution from electronic-regulated to computer-controlled analytical equipment. This holds especially true for spectroscopic instruments, e.g. FT-IR spectrometers and FT-NMR spectrometers, where the application of Fourier transform techniques requires computer support. But Chromatographic instruments are nowadays also equipped with dedicated computers or PCs for controlling the instrument and for data acquisition and evaluation.

The development has led to an improved performance of the instruments in terms of enhanced information, sensitivity, and reliability. These modern analytical instruments can be used favorably for the analysis of coatings and coating materials, making them a valuable tool for the analyst working in this field. In this paper the most important methods will be described and illustrated with examples from daily work.

Since coating materials very often represent complex mixtures, in some cases the combination of different instrumental methods is necessary to obtain the required information. Examples that will be dealt with are pyrolysis-GC/MS and the coupling of Chromatographic and spectroscopic methods, e.g. GPC/FT-IR or GPC/FT-NMR.

In many cases a work-up procedure as a preparatory step prior to the instrumental method is advisable in order to achieve sufficient information. Since many of the coating materials contain saponifiable groups, saponification is still the most prominent method. A general scheme for carrying out such a saponification will be outlined. In addition, we would also like to demonstrate a recently developed method using trimethylsulfonium hydroxide as the reagent. This method, which can be easily applied in the same way as the well-known GC derivatization procedures, yields more reliable results for fatty acids and polyols than the conventional method.
Applications of FTIR to Paint Analysis
Authors: Hartshorn JH
Published: March 2009

The value of infrared spectroscopy to the coatings industry has long been recognized. Now Fourier transform infrared (FTIR) equipment is replacing dispersive instruments because it is much faster, more accurate, and more sensitive. Of even greater impact is its data processing capabilities. Together, these advances enable the paint analyst to generate information which would have been impossible a few years ago. Applications of this technique to problem solving, cure and weathering studies, and quality control will be reported.

The extraction and identification of minor components and contaminants is one of the most difficult and time-consuming problems for the coatings analyst. The computational power of the FTIR spectrometer permits the point-by-point subtraction of one spectrum from another. The differential spectrum reveals minor differences, which are the other components in the system. This spectral stripping detects constituents which would be difficult, if not impossible, to isolate by chemical means. If the samples are skillfully prepared and subtractions carefully performed, even the concentration can be estimated. Further, the differential spectrum can be identified via computer searching of spectral libraries. This makes problem solving, such as contaminant detection and identification, rapid and effective.

Another difficult task for the coatings chemist is determining the chemical mechanisms of cure, weathering, and degradation. FTIR is providing new, valuable information about these processes. By taking and storing high-precision spectra at frequent, regular intervals, a moving picture of the process can be recorded. We call this technique “Time Lapse IR spectroscopy.” Changes in band intensity are an indication of the chemical reactions taking place within the film. These spectral shifts can be measured quantitatively so that not only the path but also the rate can be determined. Weathering studies are now being carried out after the development of a durable substrate. This provides a useful chemical picture of what is taking place during cure, weathering, or degradation.

FTIR will likely make its greatest contribution to the coatings industry as a quality assurance tool. Du Pont's Finishes Division has developed and deployed a unique instrumental package, called CATS© (Compositional Assurance Testing System). By combining a horizontal attenuated total reflectance (ATR) sampling attachment with a FTIR spectrometer and proprietary software, we have a most effective test for raw materials, intermediates, and finished products. An operator with minimum training can run the spectrum of an incoming material and decide on its acceptability within minutes. If the material is mislabeled or contaminated, it can further be identified and dealt with before a serious problem develops. This eliminates much wasted manufacturing time and material.
FTIR Techniques for the Analysis of Coating Problems: Solid Sampling Accessories
Authors: Millon AM , Julian JM
Published: March 2009

The many advantages provided by Fourier transform infrared (FTIR) spectrophotometers over dispersive instrumentation have made infrared spectroscopy even more valuable for the analysis of difficult coating samples. Established surface analysis techniques, such as attenuated total reflectance (ATR) and specular reflectance, still find wide-spread use as problem-solving techniques for cured coating systems. However, the increased energy throughput of FTIR instrumentation has made possible the development of many additional sampling accessories that have greatly simplified the analysis of coating problems. Among these new accessories are the diffuse reflectance (DRIFTS) accessory, the infrared microscope, and the photoacoustic cell. A description of these accessories, associated sampling techniques, and the use of each for the analysis of coatings and surfaces will be discussed.
Effect of Stress State on the Ductile Fracture Behavior of Large-Scale Specimens
Authors: Roos E , Eisele U , Silcher H
Published: March 2009

It is well-known from experimental investigations that at specific test conditions and specimen dimensions a sudden fracture, that is, a fracture without or after very confined plastic deformation, can occur even for materials that are characterized by small-specimen results as “tough materials.” This effect usually is defined as a constraint effect without further explanation as to how to describe constraint.

Different constraint definitions were considered originating from theoretical investigations of well-known stress and deformation states of idealized nondamaged structures. As a result of these considerations, the quotient of multiaxiality q is used to analyze the constraint effects on large scale specimens made of steels of different toughness.

It is possible to define a critical q-value as a local fracture criterion. From the location of this qc-value in the ligament of the specimen and from the variation of the q-values in the ligament, it is also possible to assess whether stable crack growth will occur or not.
Quantitative Assessment of the Role of Crack Tip Constraint on Ductile Tearing
Authors: Brocks W , Schmitt W
Published: March 2009

The quantities describing constraint and triaxiality and their relation with each other are discussed for various loading conditions and specimen geometries by comparing numerical simulations of crack growth based on the J-integral concept and on micromechanical damage models with the corresponding experiments.

It is shown that the “geometry dependence” of JR-curves is a natural feature due to different patterns of plastic flow and micromechanical processes depending on the local stress state. Hence, this dependence cannot and should not be overcome by manipulating the definition of J. A pragmatic definition of a local triaxiality parameter is given that gives reliable and reproducible results. A linear relationship is found between the triaxiality and the tearing modulus of various specimens of the same material.
Effect of Constraint on Specimen Dimensions Needed to Obtain Structurally Relevant Toughness Measures
Authors: Kirk MT , Koppenhoefer KC , Shih CF
Published: March 2009

This study examines the feasibility of predicting the fracture toughness for structurally relevant situations (shallow cracks in thick plates) based on toughness values measured with experimentally convenient specimen geometries (deep cracks in small specimens). The cleavage fracture toughness, Jc, of ASTM A515 Grade 70 steel plate was measured using single edge notch bend specimens. Specimen size and initial crack depth were varied to obtain Jc values over a range of constraint conditions. The results of these experiments indicate that crack depth and thickness cannot be traded off against each other to achieve the same constraint and thereby the same fracture toughness. The absence of this simple trade-off is due to the greater effect of crack depth than of specimen size on Jc and to the scatter in fracture toughness data characteristic of temperatures in the transition range. Alternative techniques for determining structurally relevant toughness measures from specimens based on recently proposed constraint parameters were therefore examined. These various parameters divide into two categories: those which index constraint and those which correct for constraint. Application of these constraint parameters to the A515 data indicate that all of the currently proposed techniques can account for the constraint-induced changes in cleavage fracture toughness. However, the feasibility of applying these techniques during a structural fracture safety assessment depends upon the experimental complexity and cost associated with fracture toughness determination and the ease with which the constraint parameter can be calculated for a structure.
Lower-Bound Initiation Toughness with a Modified-Charpy Specimen
Authors: Bonenberger RJ , Dally JW , Irwin GR
Published: March 2009

Lower-bound initiation toughness of A533-B (UNS #K 12539) reactor grade steel was determined over the temperature range from 0 to 57°C by using a modified-Charpy specimen. The lower-bound measurements were attained by utilizing the following procedures: (1) dynamic loading, (2) modification of the geometry of the specimen, and (3) axial precompression of the notch. The paper describes in detail the key features of the modified geometry, the method of precompressing the specimens, and the strain gage procedure. The dynamic initiation toughness KId, which correlates with the lower-bound toughness, was determined by analyzing straintime records from the specimen. The results from a fractographic analysis were correlated with those from the strain-time analysis. An empirical correlation was developed relating KId to the energy absorbed (Ecv) during the fracture of the specimen. Finally, the lower-bound toughness from this study compared favorably with KIa and KId measurements from the same material, established in other programs.
Energy Dissipation Rate and Crack Opening Angle Analyses of Fully Plastic Ductile Tearing
Authors: Turner CE , Braga L
Published: March 2009

The effects of geometry on the JR-curve for ductile tearing toughness of a titanium alloy are investigated in a series of notch bend tests taken to large amounts of growth in the fully plastic regime. For this material there is a remarkably small effect of thickness over a nine-fold range from 4 to 35 mm, but for thicknesses of 17.5 mm and greater, the R-curves are lower for wider specimens. The results are then analyzed in terms of energy dissipation rate and crack opening angle. Both terms fall rapidly just after initiation and pass to a near steady-state regime after about 10% growth. In steady-state tearing the crack opening angle is substantially constant with growth, while the steady-state dissipation rate can be split into areal and volumetric components.

It is concluded that stable ductile tearing of this material at limit load conditions is controlled by processes of plastic deformation that, if expressed as conventional R-curves, show a definite dependence on width. However, interpretation by either crack opening angle or dissipation rate model is sensitive to how the data are analyzed. The dependence of the models on the degree of plane stress or plane strain is not yet clear so that extrapolation to other sizes of specimens is still uncertain.
Size Limits for Brittle Fracture Toughness of Bend Specimens
Authors: Faucher B , Tyson WR
Published: March 2009

Fracture toughness data obtained previously from three-point-bend 10-mm, 20-mm, and 50-mm-thick side-grooved specimens and from 10-mm-thick plain-sided specimens are reanalyzed with respect to constraint. The test temperatures were low enough for the grade of steel used to ensure brittle fracture without any initiation of ductile tearing; nevertheless, extensive crack-tip blunting was observed at the highest temperatures, resulting in a highly nonlinear load-deformation behavior. Fracture toughness was evaluated from the J-integral value at the onset of brittle fracture, Jc. An equivalent stress intensity factor KJ was then obtained from the relation Kj2 = E'JC. The elastic stress intensity factor, Kc, is shown to be equal to Kj for specimen thicknesses down to half the size requirements of ASTM E 399. The macroscopic constraint, defined from the load-carrying capacity of the specimens, is independent of thickness for side-grooved specimens over the range of thicknesses studied in this work; however, it decreases slightly for plain-sided specimens. The results indicate that even when the validity limits for plane-strain fracture toughness evaluation as specified in ASTM E 399 are largely exceeded, it is still possible to measure plane-strain toughness of brittle materials using the J-integral. The results suggest that the validity limits of ASTM E 813 for measurement of cleavage fracture toughness should be increased by a factor of about two.
Influence of Out-of-Plane Loading on Crack Tip Constraint
Authors: Schwartz CW
Published: March 2009

The strains parallel to the crack front for a circumferential flaw in a pressure vessel are tensile, as opposed to zero (plane strain) or compressive (plane stress). It is reasonable to expect that this tensile strain condition may influence the constraint at the tip of the circumferential flaw. A series of axisymmetric nonlinear finite element analyses have been performed to investigate the nature of the crack tip stress fields and constraint for the limiting case of a continuous inner circumferential flaw, with an emphasis on comparing these fields and constraint levels to those in a plane strain configuration having the same geometric configuration and subjected to axial loading only. The focus of these investigations is on constraint implications for cleavage initiation in the lower transition region at realistic pressure vessel load levels; in addition, the results provide some insight into constraint implications for ductile fracture under higher load levels. Constraint is quantified using: (a) the extent of the yielded zone, (b) a hydrostatic stress triaxiality factor, (c) the elastic second-order stress term (T-stress) and the near tip elastic-plastic second-order stress term (Q-stress—O'Dowd and Shih, 1991 [24]). The analysis results suggest that the cleavage-relevant constraint measures for the circumferential flaw under combined internal pressure, crack face, and axial loading are comparable in magnitude to those in the corresponding plane strain condition at low J values; at higher J values, however, the circumferential flaw under combined loading exhibits significantly lower constraint levels than those in the plane strain reference condition. The reduction in constraint at higher J values in the circumferential flaw case is found to be caused principally by the negative in-plane stress biaxiality induced by the internal vessel pressure loading rather than by the out-of-plane tensile strain influence.
Influence of Stress State and Specimen Size on Creep Rupture of Similar and Dissimilar Welds
Authors: Kussmaul K , Maile K , Eckert W
Published: March 2009

Small-scale tension specimens taken transversely from similar weldments of 12% Cr steel as well as small- and large-scale specimens from dissimilar weldments of 12% Cr/1% CrMoV with 12% Cr deposit were tested to obtain creep rupture data at 550°C. For the similar weld, the rupture time of the specimens was considerably longer than the rupture time determined in uniaxial creep tests of the weakest heat-affected zone (HAZ) microstructure. Results of finite element analyses have shown that this is caused by a constraint imposed on the weakest HAZ by the surrounding microstructures with higher creep strength. For the dissimilar weld, the creep rupture strength of large-scale specimens is higher than that of small-scale specimens. Finite element analyses have shown differences in the stress states developing in small- and large-scale specimens, which lead to different rupture times.
Predictions of Specimen Size Dependence on Fracture Toughness for Cleavage and Ductile Tearing
Authors: Anderson TL , Vanaparthy NMR , Dodds RH
Published: March 2009

A framework for predicting the effect of crack-tip triaxiality on fracture toughness is outlined. This methodology is a two-parameter approach that considers the micromechanism of failure. A local damage parameter is used in conjunction with a crack-tip stress analysis to predict the effect of specimen dimensions on toughness. In the case of cleavage fracture, the local criterion involves the maximum principal normal stress, σ1 as well as the volume over which σ1 acts. The agreement between predictions and experimental data is very good in this case. for initiation of ductile tearing, we defined a damage parameter based on a modified version of the Rice and Tracey hole growth model. The analysis indicates that ductile fracture is less sensitive than cleavage to triaxiality. While this result is broadly consistent with experimental observations, further work is necessary to develop improved local criteria for ductile fracture.

The micromechanics approach proposed by the authors was compared with two-parameter fracture mechanics methodologies based on continuum theory, such as the K-T and J-Q approaches. These continuum methodologies, which involve two-term expansions of the crack tip fields, are descriptive rather than predictive. That is, these approaches describe the crack tip triaxiality, but they do not predict the effect of triaxiality on fracture behavior. The micromechanics approach, however, was developed for the purpose of making such predictions. Thus, the continuum and micromechanics approaches to two-parameter fracture mechanics are complementary.
High Strain Rate Testing and Structural Analysis of Pericardial Bioprosthetic Materials
Authors: Lee JM , Haberer SA , Pereira CA , Naimark WA , Courtman DW , Wilson GJ
Published: March 2009

Characterization of the viscoelastic behavior of pencardial biomatenals for heart valve or patching applications demands testing under loading times or frequencies typical of those that occur in physiological function or in a bioprosthetic device We have used a servo-hydraulic testing system to evaluate the behavior of these materials under loading times as low as 0.05 s, frequencies up to 10 Hz and strain rates exceeding 24 000 %/min Mechanical tests included large deformation cyclic loading, stress relaxation experiments, and small deformation forced vibration This paper reviews our expenence with these tests, interpreted using results from collagen denaturation temperature testing and biochemical analysis, in three distinct studies: (1) examination of the effects of glutaraldehyde, poly (glycidyl ether) (a diepoxide compound), and cyanamide on bovine pericardium, (2) comparison of bovine and porcine pericardia, and (3) evaluation of the effects of extraction of cellular components from bovine pericardium These tools provide better means toward understanding the viscoelastic properties of these materials and the structural/functional relationships that determine those properties.
A New Method for In-Vitro Wear Assessment of Materials Used in Mechanical Heart Valves
Authors: Teoh SH , Lim SC , Yoon ET , Goh KS
Published: March 2009

Accelerated life testing has been in use for a number of years to study the long-term in-vitro durability of heart valves. These tests were designed to test concurrently the durability of the materials and design of the heart valves. However, problems interpreting the results and relating them to actual clinical applications were encountered. Current view is that the life testing of mechanical heart valves can best be performed by partitioning the in-vitro wear assessment of the material separate from that due to the overall design of the heart valve. A new method, simulating the impact-cum-shding action in mechanical heart valves, at a low frequency, was developed to test a variety of candidate materials polyoxymethylene (Delrin), polyetheretherketone (PEEK), polyethersulphone (PES), and ultrahigh molecular weight polyethylene (UHMWPE). The results were compared with those reported earlier in published literature. The damage features seen on the different test specimens and the wear debris produced were similar to those found on an explanted heart valve of more than 17 years old, supporting that the present technique could simulate the wear conditions in mechanical heart valves. The technique saved time and was amenable to wear mechanisms study using the scanning electron microscope (SEM). The wear results showed that, in terms of maximum wear depth, UHMWPE wore the least followed by Delrin, PEEK, and PES There does not appear to be any correlation between wear and the molecular weight of Delrin. The incorporation of 0.3% carbon did not improve the wear performance of Delrin. Both UHMWPE and PES produced debris that were significantly larger than the rest. Because of the possibility of dislodgement of large debris in the range of 100 μm or more, UHMWPE was not considered to be a good matenal for use as occluder in mechanical heart valves even though it wore the least. At present, Delrin is still considered to be the best occluder matenal examined PEEK showed good potential but longer expenments need to be earned out in order to show its full potentiality PES showed the worst wear characteristics.
The Relationship Between PTFE Graft Ultrastructure and Cellular Ingrowth: The Influence of an Autologous Jugular Vein Wrap
Authors: Holubec H , Hunter GC , Chvapil M , Chvapil TA , Bernhard VM , Misiorowski RL , Putnam CW
Published: March 2009

Here, we report the differential effects on cellular ingrowth and healing caused by varying the mternodal distance (IND) of polytetrafluoroethylene (PTFE) grafts. In addition, we examined whether cellular ingrowth could be enhanced by an additional source of endothelial cells. Both carotid arteries of greyhound dogs were replaced with 5-cm lengths of 4-mm-diameter PTFE grafts of varying IND (30, 40, 60 μm). The histologic characteristics of anastomotic and midgraft segments of grafts wrapped with autologous vein graft as a source of endothehal cells were compared to the contralateral unwrapped graft of identical IND. At five weeks the grafts were excised and examined histologically and the in vivo IND, cellular and microvessel ingrowth, and endothelialization of the luminal surface quantitated. All 30 μm grafts (N = 8) were occluded by anastomotic pannus ingrowth (PI). The anastomoses of 40 and 60 μm grafts were characterized by either intimal hyperplasia (IH) (N = 10) or healing with minimal intimal thickening (H) (N = 4). The mean reduction in IND at anastomoses was 68 to 75% for all grafts whereas midgraft IND was unaffected. The mean IND at anastomoses with PI was 7.0 ± 1.5 μm, IH 12.0 ± 2.5 μm, and 19.0 ± 2.0 μm for healed anastomoses. Midgraft cellular ingrowth was greater than that observed near anastomoses and varied with IND. The application of a vein wrap enhanced cellular and microvessel ingrowth and endothelialization of 40 and 60 μm grafts. These data suggest that alterations in PTFE ultrastructure likely resulting from surgical manipulation during implantation may adversely influence anastomotic healing.
The Effect of Tissue Adhesion Due to Encapsulation on Anastomosis Strength and a Comparative Study of Vascular Substitute
Authors: Yokobori AT , Maeyama T , Kuroda S , Yokobori T , Ohuchi H
Published: March 2009

The anastomosis strength of vascular substitute and blood vessel is supported not only by the suture thread but also by tissue adhesion due to encapsulation of vascular substitute In this paper, the in vitro and combined in vivo and in vitro mechanical tests were earned out to estimate the anastomosis strength between a vascular substitute and a blood vessel, good encapsulation of inner wall of the vascular substitute around the anastomosed part was found to be effective to enhance anastomosis strength Furthermore, these results were compared with the expenmental result of the anastomosis being performed by using suture thread only Concerning the problem of the anastomosed part of the blood vessel with the vascular substitute, both effects mentioned above were found to be important requisites for the design of good functional vascular substitutes suitable for anastomosis Finally, the significance of the in vitro and combined in vivo and in vitro mechanical tests are discussed
Mechanical Properties of Immature Callus in Long Bones
Authors: Miyasaka Y , Ohyama M , Sakurai M , Yokobori AT , Sasaki S
Published: March 2009

Callus distraction had long been believed to be harmful to fracture healing until the development of a new method named callotasis, which gave the green light to the field of long bone lengthening. This revolutionary method showed that the distraction does not disturb bone formation, which was confirmed by our results of clinical cases. One of our callotasis cases was presented to show its characteristic X-ray features in the course of callotasis.

We made experimental callotasis in rabbit femurs and performed mechanical tests for callus of the bones in order to investigate its mechanical behavior when tensile loads were applied. Femurs of eight rabbits were osteotomized at the level of the midshaft with a bone saw and fixed with a mini-model external fixator. Gradual callus distraction was performed at the rate of about 0.7 mm per day. The femurs were removed after sacrifice and served as bone specimens for the mechanical tests. Control long bones were twelve osteotomized femurs fixed with the same external fixator without callotasis and ten osteotomized tibiae fixed with an intramedullary Kirschner wire.

This immature callus showed the characteristics of hysteresis in the load-deformation curves and also those of stress relaxation in stress relaxation test. We conclude that the callus in callotasis has the property of viscoelasticity, and infer that this property is one of the mechanical bases making callotasis possible.
Evaluation of Mechanical Properties of Metallic Biomaterials
Authors: Higo Y , Tomita T
Published: March 2009

In this paper, some methods for evaluating the properties of metallic biomaterials are proposed and discussed, with special interest in the requirements of biomaterials which strongly relate to corrosive properties. A simple evaluation method for determining metallic elution was proposed, and the results are shown.

The most important mechanical property of a biomaterial is the fatigue life under consideration of actual usage and environment. The methods employed for the artificial joint were used as an example. The appropriate fatigue test for the biomaterial component is a four-point side notch bend specimen and the dimensions of the specimen are given. The notch tip radius of curvature should be the smallest radius of curvature of the implant design. The notch tip surface finishing condition should especially be examined, because not only notch radius (stress concentration) but also notch surface condition (scratch and structure sensitivity) affect the fatigue properties. The corrosion characteristics of biomaterials are also estimated by measuring the difference of the fatigue life in a laboratory air environment to that in a physiological saline solution environment. The details of the results on pure titanium, titanium alloy, and stainless steel are given.
Mechanical Testing for Fretting Corrosion of Modular Total Hip Tapers
Authors: Flemming CAC , Brown SA , Payer JH
Published: March 2009

A recent advancement in the design of the total artificial hip is the introduction of modularity. Within the last year clinical retrievals have shown that significant corrosion can occur at the cone-taper interface in some variations of the modular hip. The hypothesis of this study was that the stability of the cone-taper interface affects the amount of fretting corrosion that occurs. The development of a method that can study the taper corrosion and determine the most stable design is therefore necessary.

Design characteristics that may affect corrosion include the use of dissimilar metals, taper angle, taper diameter, percent coverage, machining tolerance, and head neck extension. The fretting that occurred at the interface was initially studied by measuring potential changes while cyclically loading hips in a universal testing machine. This method of measurement proved ineffective at isolating the fretting at the taper interface so current changes were monitored instead. The current was measured when the saline was below the crevice and when it was just above the crevice, and the two measurements were subtracted from each other to produce the taper fretting current.

When comparing two different designs, one showed a significant taper fretting current while the other's was minimal. In a second study, when comparing two different head neck extensions placed on identical stem designs, a significant taper fretting current was seen with the + 10-mm head as compared to a +0-mm head. It is concluded that this method can be used in the evaluation of designs to optimize stability and reduce the resulting fretting corrosion.
Cell-to-Materials Interaction—An Approach to Elucidate Biocompatibility of Biomaterials In Vitro
Authors: Nakamura M , Takeda S , Imai K , Oshima H , Kawahara D , Kosugi H , Hashimoto Y
Published: March 2009

The biomaterials used in the oro-maxillo-facial region, in particular the oral cavity, center of the region, require unique biocompatibility characteristics compared to those for other parts of the body. Cell-to-material interaction is a key approach in elucidating such aspects as biological, mechanical, and chemical compatibility of biomaterials in vitro. The results obtained by the in vitro tests under dynamic conditions mimicking the functions of this region are considered to better reflect the material's behavior in vivo than those obtained by the conventional, static testing methods. We have obtained data different from those obtained by the conventional methods. A simulation approach appears to be necessary to elucidate biocompatibility. Also, the measurement of the adhesive strength of cells on biomaterials is important in elucidating the cell-to-biomaterial interaction. Further refinement of methods is essential for standardization.
The Use of Small-Scale Flexure Test Specimens to Evaluate the Mechanical Properties of Polymer Composites for Biomaterials Applications
Authors: Jockisch KA , Brown SA , Moet A
Published: March 2009

Miniflexbars (MFBs), 1 by 5 by 30 mm, which are tested in three-point bending, have been used to study the mechanical properties of polymer composites. Chopped carbon fiber reinforced polyetheretherketone (PEEK) injection-molded bendbars, 6 by 12 by 120 mm, were chosen for analysis. MFBs were cut parallel and perpendicular to the mold fill direction from four sections of the standard size bendbar. Results of the flexure testing indicated that the strength of the MFBs was significantly decreased from the strength of the standard size bendbar. Strength also varied with position of the MFB in the standard size bendbar. To better understand these results, several factors were evaluated. Upon cutting the MFBs from the injection-molded bar, residual stresses were relieved. The decrease in strength, however, could not be associated entirely with the release of residual stresses. Local fiber orientation was examined with light microscopy. Results from this analysis indicated that flexure testing of MFBs is sensitive to local variation in microstructure. Evaluation of an injection-molded chopped fiber composite bend-bar using MFBs has indicated that these small-scale specimens can provide valuable information about the mechanical properties of polymer composites. With this understanding, MFBs can be used, with caution, in the development of in vitro and in vivo accelerated degradation test methods as well as other biomaterials applications.
A Numerical Time-Frequency Transform Technique for the Determination of the Complex Modulus of Composite and Polymeric Biomaterials from Transient Time-Based Experiments
Authors: Gilbert JL , Dong DR
Published: March 2009

A numerical time-frequency transform technique is described that can be used to determine the complex modulus of a material as a function of frequency from stress relaxation experiments. This technique uses analog-to-digital data acquisition techniques to obtain the time domain response over several decades of time. Numerical filtering techniques are then applied to reduce spurious noise. An exponential interpolating function is fit to the relaxation data and this function is then transformed into the frequency domain with the use of piece-wise integration of the Laplace transform. The error associated with the numerical transform technique is found to be very small (on the order of 10−4%) when analyzing ideal behavior.

An experimental apparatus is developed and used in conjunction with this technique and initial tests of poly(methyl methacrylate) (PMMA) and polyethylene (PE), and PMMA/GF composites reveal that relaxation peaks (maximums in the loss modulus) associated with molecular transitions in the polymers can be detected with this method. Modulus-temperature-frequency plots indicate that the methodology is able to detect changes in peaks with increasing or decreasing temperature and that some of these peaks appear to correlate with known molecular transitions.
Fracture Behavior of Polyurethane-Calcium Chloride Blends
Authors: Wong RP , Benson RS
Published: March 2009

Two polyurethanes and their respective 1,5, and 10 wt.% CaCl2 blends were studied. The normalized strain energy (J-) was used to characterize the fracture susceptibility of films made from the polyurethane-calcium blends. The low normalized strain energy is correlated with ease of fracture. The normalized strain energy to failure for all the Biomer®-calcium chloride blends throughout the entire range of crack lengths was less than observed for the pure Biomer. The normalized strain energy values obtained for the Biomer-1 wt.% CaCl2 were comparatively lower than all other Biomer blends. At concentrations of 5 and 10 wt.%, there was some evidence that increase in the normalized strain energy to failure could be attributed to plasticization and crack arresting behavior of the calcium chloride dissolved in the matrix. The normalized strain energy values for calcium chloride blended with Pellethane® were different above and below the critical crack length. For initial crack lengths less than the critical length, the normalized strain energy for the Pellethane-calcium chloride blends were less than for pure Pellethane. At cracks larger than the critical length, the Pellethane-calcium blends displayed greater normalized strain energy to failure. The addition of a small amount of calcium chloride to Biomer and Pellethane leads to a reduction in the normalized strain energy which can be associated with lower fracture toughness. Pellethane appeared to be more susceptible than Biomer to the deterioration of its fracture properties.
Micromechanical Testing of Interfacial Bonding in Absorbable Composites
Authors: Leadbetter KJ , Latour RA , Johnson RA , Shalaby SW
Published: March 2009

A new approach is described, involving microdroplet fiber composites, to study absorbable fiber-reinforced composites with physicochemically hybridized interfaces. Both an Instron Dynamic Test Machine and a micromechanical testing machine are successfully used to monitor variation in interfacial bond strength resulting from changes in certain key processing variables, and a comparison is made between the two test methods. It is concluded that these procedures are able to discern small interfacial adhesion strength differences and can contribute effectively to the establishment of an optimal filler-matrix interface.
Chemical Components and Mechanical Properties of Urinary Calculi
Authors: Uchida M , Imaide Y , Watanabe H
Published: March 2009

As part of a research project on the intracorporeal destruction of urinary calculi with a small dose of explosives, a study of the correlation between the chemical components and the mechanical properties of urinary calculi was made. Compressive strength, tensile strength, and modulus of elasticity under dry and wet conditions were measured to find the mechanical properties of urinary calculi. All urinary calculi in the dry condition could be classified into two groups with a borderline of 6.5 MPa for compressive strength, 1.5 MPa for tensile strength, and 600 MPa for modulus of elasticity, and most of the calculi fell below the borderline. The chemical composition of calculi belonging to the high-strength calculus group was mostly a mixture of calcium phosphate and calcium oxalate. The strength of calculi in the wet condition was less than that in the dry condition.
Tests to Evaluate the Mechanical Properties of the Ureter
Authors: Watanabe H , Nakagawa Y , Uchida M
Published: March 2009

In 1975, we started a research project for the development of microexplosion lith-otripsy. In this project, we investigated the mechanical properties of the urinary tract organs to clarify factors to prevent complications from the method. Tension and expansion tests were performed on the middle portion of the normal ureter taken from fresh cadavers in 1983.

A tension test was performed on eleven ureters in the longitudinal direction and seven in the transverse direction using a universal tensile tester. Tensile strength and maximum tensile stress in the transverse direction of the ureter were weaker than those in the longitudinal direction. Accordingly, it was presumed that ureteral injury first occurred in the transverse direction. The maximum tensile stress of the ureter was higher than that of the bladder, which was previously reported in another paper.

Expansive tests were performed on ten ureters. At the leakage point, the tensile strength and elongation ratio of the external diameter were approximately equal to the tensile strength and elongation ratio measured by tension test in the transverse direction.

It could be concluded from the results that microexplosion lithotripsy could be applicable even in the ureter under certain conditions.
Mechanical Properties and Modeling of the Stress-Strain Behavior of the Urinary Bladder In Vivo
Authors: Saitoh M , Ohnishi K , Matsuda T , Watanabe H , Yokobori AT , Yokobori T , Oki F
Published: March 2009

A stretch test in vivo for living materials was newly developed and applied to the dog bladder. The stress-strain curve of the normal living bladder was a downward convex and rose very slowly. The curve showed hysteresis and speed-dependence. These results proved that the mechanical property of the urinary bladder was essentially viscoelastic.

A computer analysis, based on the viscoelastic simulation model proposed by Glantz, was performed to evaluate the mechanical property of the bladder. Both proportional and exponential stiffness elevated in the extirpated bladder. In the denervated bladder, changes of the constants were not significant immediately after cutting the pelvic nerves; however, the proportional stiffness elevated remarkably two weeks after cutting. Compared with these abnormal bladders, the elastic constants of the normal living bladder were very low. The viscoelastic properties of the bladder and its low elastic constants seemed to account for the normal bladder function as a reservoir for urine.
Changing Strategies for Biomaterials and Biotechnology
Authors: Kambic HE
Published: March 2009

The basis for the design and fabrication of new substitutes for tissue regeneration and organ replacement resides in biomaterials science and in the emerging field of tissue engineering. Three design approaches employ materials that perform as inert, biometric or biodegradable interfaces with body fluids or tissues. Biomaterials can provide the substrate integrated with tissue engineered molecules, cells, extracellular matrix, or recombinant protein. The question remains as to how we begin to address the issue of quality, safety, and efficacy issues in experimental testing of these materials when used in medical applications. As federal government funding of research has decreased, industrial support of academic research and development has grown. As the complexity of the interactions between materials and biological tissues grows, biomaterials-based emerging technologies will prosper through an overall changing approach to basic and applied biomaterials research. How to meet these needs through industry and acade-mia remain unresolved. Our priorities must include a major emphasis on quality and strict adherence to quality assurance issues in testing and analysis.
Influence of Crack Closure and Stress Ratio on Near-Threshold Fatigue Crack Growth Behavior in Ti-1100
Authors: Parida BK , Nicholas T
Published: March 2009

In the present study, the fatigue crack growth behavior of a near-α, β-processed titanium alloy, Ti-1100, was investigated with the objective of assessing the influence of crack closure and stress ratio on fatigue threshold. Measurement of the crack-opening load in single-edge tension [SE(T)] specimens was made by near-tip strain gage and DCPD methods. Fatigue threshold stress intensity ranges, ΔKth, determined under constant stress ratio and constant maximum stress intensity, variable stress ratio conditions indicate almost identical values for R above 0.5. It is postulated that while crack closure in the wake of the crack tip is responsible for the no-growth condition in the former case, lack of sufficient damage accumulation at the crack tip as a consequence of the formation of an insignificant reversed plastic zone and large planar slip band formations surrounding the crack tip appears to be responsible for no growth in the latter case. The use of an effective stress intensity based on closure data consolidates most of the threshold data, indicating the independence of the fatigue crack growth data to mean stress or R.
Fatigue Crack Growth and Crack Bridging in SCS-6/Ti-24-11
Authors: Ghosn LJ , Kantzos P , Telesman J
Published: March 2009

Interfacial damage induced by relative fiber/matrix sliding was found to occur in the bridged zone of unidirectional SCS-6/Ti-24Al-11Nb intermetallic matrix composite specimens subjected to fatigue crack growth conditions. The degree of interfacial damage was not uniform along the bridged crack wake. Higher damage zones were observed near the machined notch in comparison to the crack tip. The interfacial friction shear strength, τf, measured in the crack wake using pushout testing revealed lower values than the as-received interface. Interfacial wear also reduced the strength of the bridging fibers. The reduction in fiber strength is thought to be a function of the magnitude of relative fiber/matrix displacements and the degree of interfacial damage. Furthermore, two different fiber bridging models were used to predict the influence of bridging on the fatigue crack driving force. The shear lag model required a variable τf in the crack wake (reflecting the degradation of the interface) before its predictions agreed with trends exhibited by the experimental data. The fiber pressure model did an excellent job in predicting both the FCG data and the ΔCOD in the bridged zone even though it does not require a knowledge of τf.
Synthesis, Strengthening, Fatigue and Fracture Behavior of High-Strength, High-Conductivity P/M Processed Cu-Nb Microcomposite
Authors: Nayeb-Hashemi H , Pourrahimi S
Published: March 2009

Materials with both high conductivity and high strength are desired in the design of magnets and rotating electrical machineries. Copper-niobium (Cu-Nb) filamentary microcomposites are such a group of materials. Powder metallurgy techniques (P/M) followed by various deformation processes were used to synthesize these composites. A restacking technique was developed to achieve the high areal reduction necessary to reduce the Nb powder particles to ultra-fine fibers within the Cu matrix. The effects of the Nb volume fraction and size on the evolution of the material microstructure, monotonic tensile properties, and fatigue and fracture behaviors were studied. A strengthening model that combines Cu matrix work hardening, fiber strength, and dispersion-type hardening was developed and shown to predict the yield strength of composites at various stages of deformation processing with reasonable accuracy.

The tensile failure of composites with fully deformed Nb fibers was a shear-type failure (a 45° plane to the specimen axis). However, for composites without fully deformed fibers, the fracture surface had a cup and cone appearance. Fatigue properties of a composite with 18 vol.% Nb and fibers at their fully deformed stage (fiber thickness of 5 to 10 nm) were studied. The mechanisms of crack initiation and propagation were investigated. The final composite failure was due to tensile overload rather than attainment of critical crack length.