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Seven laboratories participated in an interlaboratory study to assess the applicability of ASTM E606, Test Method for Strain-Controlled Fatigue Testing, to strain-controlled fatigue of a tungsten fiber/copper matrix composite (Battelle Columbus, University of Iowa, IITRI, MCL, MarTest, Rockwell International Science Center and University of Twente). Because of the material and specimen fabrication methods, the number of fibers in the 9, 25, and 36 % fiber volume fraction specimens is approximately the same and the strain-life data are nearly identical for each of the volume fractions. Although the specimen aspect ratio is within the nominal range, the specimen diameter is less than the nominal value specified in ASTM E606. Laboratories reporting data noted that a small specimen diameter and a large gage section aspect ratio made specimen alignment difficult. Thus, specimen buckling was problematic at high strain ranges. The study data are reported and analyzed with nonparametric and semiparametric statistical methods to assess the effect of study covariates on fatigue life. The median fatigue life, median absolute deviation from the median, and interquartile range are reported as measures of central tendency and variability. ASTM E606 may be used as a guide to evaluate the fatigue response of this type of composite material if the length-to-diameter aspect ratio, specimen alignment in the fatigue machine, and specimen surface finish are closely monitored to ensure valid data.

ASTM E2948, Standard Test Method for Conducting Rotating Bending Fatigue Tests of Solid Round Fine Wire, is a procedure for rotating bending fatigue tests of fine wire to obtain the fatigue strength for metallic materials at a specified life in the fatigue regime where the strains are predominately and nominally linear elastic. This method is limited to the fatigue testing of small diameter solid round wire subjected to constant amplitude, completely reversed, periodic strain. The methodology can be useful in assessing the effects of inclusions, melt technique, and cold work processing. Data obtained in accordance with ASTM E2948 is subject to variability because of many factors. An inter-laboratory study (ILS) was performed to assess variability of the data and to develop a precision statement for ASTM E2948. Ten laboratories participated in the ILS. The samples consisted of two materials, Nitinol and 35N LT. Each material was supplied from a single lot from a single manufacturer. Samples were tested at three different strain amplitudes with ten replicates at each strain level. Variability of the resulting data was quantified as reproducibility limits, between laboratory variability, and repeatability limits, within laboratory variability. A precision statement for ASTM E2948 was formulated based on the reproducibility and repeatability limits determined from the inter-laboratory study. The viability of the limits is assessed with Monte Carlo simulations. Alternative methods of analysis using nonparametric statistics and bootstrap methods are discussed.

Studies in fatigue can be summarized into two stages, fatigue crack initiation and crack propagation. Fatigue damage may increase the risk of failure under cyclic load. Energy dissipation, termed damping, occurs in engineering metals and is a function of the cyclic loading history. Damping behaviour of materials has been estimated using many different experimental techniques, and parameters i.e. the loss factor vs. strain amplitude, frequency range, etc. However, micro-structural changes in the form of fatigue damage are also contributors to damping in engineering materials. In order to measure energy dissipation, a damping monitoring method has been used. Under a constant cyclic load up to the point of fatigue crack initiation, the effects of fatigue on damping factor were studied for 6061-T6511 aluminium alloy. In the experiments, the stress levels were below yield point, 50% and 70% of ultimate strength. Experimental results showed that the damping factor changes with the number of fatigue cycles. Percentage increase in damping energy was calculated using experimental data.

Hot Isostatic Pressing (HIP) is used extensively for consolidation of powers and particulates and near net shape fabrication of powder metallurgy products. The last few years have seen significant refinement of the HIP model proposed by Ashby and co-workers. It has been acknowledged by the developers of the maps that the accuracy of the predictions is limited by the precision with which material property data, used in the HIP Maps program are known. Even for materials processed similarly, there are, typically, variations in the values of material properties due to the inherent inaccuracies in the methods used to determine these properties. Such variations significantly affect the accuracy of the HIP model predictions. The objective of the present investigation is to determine the effect of variations in the values of material properties on the HIP model predictions by performing a sensitivity analysis with respect to material property data. The values for material property data used in the HIP Maps program are typically determined in one of the following ways: (a) experimental measurements at consolidation conditions; (b) estimates based on data on other materials; (c) through back calculations using the experimentally determined HIP data; and (d) by extrapolations to get appropriate materialmore » property values for the consolidation conditions. Methods other than (a) could result in the determination of a material property value which is highly unrealistic. The present study discusses this with respect to a recent experimental study [10] on TiAl and resolves the discrepancy by using PLC material parameters determined experimentally for conditions close to the actual HIP process conditions.« less

The use of an analytical model for determining the moduli of elasticity of composite laminates made of woven or unidirectional plies with different porosity levels was described. The analysis of aircraft composite parts with different levels of voids (porosity) was based on a method which utilizes the results of state-of-the-art nondestructive testing methods (ultrasonic through transmission, loading, or pulse/echo) as the starting data for the analytical model. The porosity distribution over the volume of the material and correlations for the nondestructive testing methods were determined for epoxy-carbon laminates with standard and stiffened binders and corroborating experiments were conducted. It was shown that the moduli of elasticity of composite laminates decrease with an increase in the porosity levels. The type, thickness, and layup of the laminate are the basic factors that affect the decrease in the elastic properties of porous composite laminates.

The chemical and biomechanical properties of explanted implants whose time of implantation ranged from zero to 21 years were measured. The properties appear to decrease with time. However it is important to note that proper controls have yet to be tested. The consistency of the gel varied considerably with manufacturer and date of manufacture. The data will be correlated with control samples when they become available. The data are consistent with the hypothesis that in some instances, the gel does affect the cross-linking, i.e., strength, of the silicone rubber shell. At the present time only a limited number of samples have been tested in this on-going program. One of our major objectives, to determine the influence of the physiological environment of the human body on the durability of the silicone implant, has yet to be quantified.

The paper addresses the Plastic behavior of the aluminum alloy 5086 and 5454 in the H-32 temper under cyclic load. It reports the experimental results and analyzes them with the aim to design constitutive laws which could be used in the computational analysis. The reliability of the constitutive laws is analyzed.

Previous chapters of this book have discussed the wetting behavior of near-eutectic Sn-Pb solders. These alloys are the most common in electronic applications and are deserving of the greatest attention. However, there are many applications where the properties of these alloys can be improved. A composite solder, or a solder that contains second-phase dispersions of particles, could improve solder joint properties. The area where composite solders could have the greatest impact is in improving the mechanical properties of the joint. However, the wetting behavior of the solder cannot be compromised for the sake of the mechanical properties -good wetting behavior is a necessity. Therefore, for a composite solder to be useful for electronic packaging applications mechanical properties, wetting and manufacturability must be optimized.

Substantial improvements have been reported in high temperature strength and creep resistance, and room temperature fracture toughness of molybdenum disilicide (MoSi2) reinforced with ductile or brittle reinforcements. The influence of Hot Isostatic Pressing (HIP) process parameters on the mechanical properties of MoSi2 based alloys was studied. Monolithic MoSi2 powder and MoSi2 powder blended with either niobium powder or silicon carbide whisker reinforcements were consolidated by HIP at 1200 − 1400°C, 207 MPa, and 1 - 4 hrs. The HIP'ed compacts were characterized for compression strength and creep resistance at 1100-1300°C. Fracture toughness was measured on single edge notched rectangular specimens at room temperature. Mechanical properties were correlated with post-HIP microstructural features.

The paper addresses the reliability of computational analysis of plastically problems in light of the experimental work and its mathematical formulation. The paper also addresses some basic constitutive laws used in engineering and proposes one which leads to a well posed mathematical problem and agrees well with the experimental data. The data of the experimental project for 5454 aluminum alloy in the H32 condition for periodic and random strains are presented. Various constitutive laws are assessed in light of the experimental data. Outstanding problems related to the reliability of the analysis are mentioned.

In addition to excellent biocompatibility and corrosion resistance, the unique flow behavior of NiTi pseudo-elastic alloys renders them ideally suited for several medical device applications utilizing minimally invasive technologies. For example, self-expanding stents are indicated chronic therapies for treatment of a variety of vascular diseases. Long-term device integrity is thus critical with the FDA recommending a minimum 10-year life. Historically, the majority of published fatigue data on NiTi alloys have been generated under strain-controlled conditions using wire or single-diamond cell samples designed to replicate the behavior of the repetitive unit within a stent. Resulting data are then presented on modified Goodman or Soderberg diagrams in order to define regions of acceptable device life. Consistent with their unusual monotonic flow characteristics these alloys are found to exhibit unique cyclic behavior in fatigue: published data clearly demonstrate that increasing mean strain often increases high-cycle fatigue life. This anomalous behavior is generally attributed to any of a number of possible microstructural or mechanical effects associated with the reversible stress-assisted austenite-to-martensite phase transformation. Although the majority of published work has focused on these macroscopic properties in order to characterize and adequately define device life, various efforts are currently underway to better understand the more fundamental metallurgical and mechanical aspects controlling fatigue life in this alloy. Such studies include crack initiation and propagation rates, determining the roles of absolute and relative inherent flow behavior of the transforming structures, mechanical instabilities resulting from the heterogeneous nature of the transformation, latent heat effects during cyclic transformation, as well as the effects of testing frequency, crystallographic texture, grain-shape anisotropy, and stress-state on fatigue life. A review of existing literature delineating these behaviors and current efforts is presented in light of known beneficial effects of transformation plasticity and toughening in enhancing fatigue and fracture properties of a variety of metallic and nonmetallic materials.

In the acousto-ultrasonic technique, a wave is injected onto the surface at one location and the displacement normal to the same surface is measured at another location. Thus, understanding the propagation characteristics of the wave is essential for successful application of the technique. The main objective of the present investigation is to identify through analysis-experiment correlation how the AU wave propagates through composite laminates.