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Specimen Geometry (specimen + geometry)
Selected AbstractsFabrication of Graded Nickel,Alumina Composites with a Thermal-Behavior-Matching ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2000Andrew N. Winter Composites of nickel and Al2O3 with compositionally graded microstructures were fabricated from powders through an empirically determined thermal-behavior-matching process that was designed to minimize processing-induced stresses. Compositions ranged from pure Al2O3 to pure nickel. Specimen geometries included round disks 25 mm in diameter and 5,25 mm thick, as well as rectangular bars 25 mm × 25 mm in cross section and 75 mm long. Several different gradients were produced, including samples with single interlayers. Compacts were formed by cold uniaxial pressing in a die, followed by consolidation through sintering at 1 atm or hot isostatic pressing. Several different particle sizes of nickel and Al2O3 comprised the composite interlayers. The compaction behavior, sintering start temperature, sintering rate, and total linear shrinkage of each composition were evaluated. Careful data analysis, coupled with sintering theory, led to a layer configuration with matched green density and sintering behavior. Thermomechanically matched layers allowed large, crack-free, graded composites to be produced. [source] Evaluation of creep damage accumulation models: Considerations of stepped testing and highly stressed volumeFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2007W. A. GRELL ABSTRACT Many components experience combined temperature and stress loading and are designed to withstand creep. In this study, experimental creep testing was performed under both static and stepped loading conditions with constant temperature for two specimen geometries (tensile and three-point bend). The objective of this study was to evaluate whether existing damage accumulation models accurately predict creep performance when considering step loading and stress gradients. Model predictions, based on static tensile creep data and using a highly stressed volume correction for the three-point bend specimens and the experimental average damage sum, agreed well with experimental data; differences were on average within 38% (static) and 2.2 h (stepped). Comparisons showed more accurate predictions using an exponential Larson,Miller parameter curve and the Pavlou damage accumulation model. Findings of the current study have applicability to component design, where complex geometries often contain stress gradients and it is desirable to predict creep performance from static tensile creep data. [source] Effect of hardness on multiaxial fatigue behaviour and some simple approximations for steelsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2009N. SHAMSAEI ABSTRACT Constant-amplitude in-phase and 90° out-of-phase axial-torsional fatigue tests were conducted on tubular specimens made from a medium-carbon steel with three hardness levels obtained from normalizing, quenching and tempering and induction hardening to find the effect of hardness on multiaxial fatigue behaviour. In addition, the same loadings were applied on the normalized solid specimens to investigate the effect of specimen geometry on multiaxial fatigue life. Similar fatigue life variation as a function of hardness was found for in-phase and out-of-phase loadings, with higher ductility beneficial in low-cycle fatigue (LCF) and higher strength beneficial in high-cycle fatigue (HCF). Multiaxial fatigue data were satisfactorily correlated for all hardness levels with the Fatemi,Socie parameter. Furthermore, in order to predict multiaxial fatigue life of steels in the absence of any fatigue data, the Roessle,Fatemi hardness method was used. Multiaxial fatigue lives were predicted fairly accurately using the Fatemi,Socie multiaxial model based on only the hardness level of the material. The applicability of the prediction method based on hardness was also examined for Inconel 718 and a stainless steel under a wide range of loading conditions. The great majority of the observed fatigue lives were found to be in good agreement with predicted lives. [source] Off-axis electron holography of electrostatic potentials in unbiased and reverse biased focused ion beam milled semiconductor devicesJOURNAL OF MICROSCOPY, Issue 3 2004A. C. TWITCHETT Summary Off-axis electron holography in the transmission electron microscope (TEM) is used to measure two-dimensional electrostatic potentials in both unbiased and reverse biased silicon specimens that each contain a single p,n junction. All the specimens are prepared for examination in the TEM using focused ion beam (FIB) milling. The in situ electrical biasing experiments make use of a novel specimen geometry, which is based on a combination of cleaving and FIB milling. The design and construction of an electrical biasing holder are described, and the effects of TEM specimen preparation on the electrostatic potential in the specimen, as well as on fringing fields beyond the specimen surface, are assessed. [source] Friction evaluation of elastomers in lubricated contactLUBRICATION SCIENCE, Issue 10 2009Gregory F. Simmons Abstract Friction testing of elastomers in lubricated contact is discussed with a focus on developing experimental arrangements that can produce worthwhile results. Practical issues unique to elastomers are covered as well as their solutions, including contact mechanics, material response to loading, contact edges, oil absorption, cleaning and specimen geometry. A critique of reciprocating laboratory testing machines, including high-frequency short stroke and low-frequency long stroke friction and wear machines, is conducted for their usefulness, as is critical analysis of a wide variety of specimen configurations with the aim of helping the laboratory experimenter to overcome many of the pitfalls associated with testing of elastomers in lubricated conditions. Results from experiments using various testing arrangements are analysed, and it is found that the synthetic ester and mineral oil used produced similar results. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effect of Sample Configuration on the Morphology of Foamed LDPE/PP Blends Injection Molded by a Gas Counterpressure ProcessMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2007Georgi Kotzev Abstract Blends of isotactic poly(propylene) and low-density polyethylene with different composition ratios were prepared through direct melt compounding on a twin-screw extruder. The specimens with various geometric configurations were injection-molded using a gas counterpressure process, using blends to which 0.5 wt.-% of a blowing agent was added. The influence of blend composition and specimen geometry on the structure and morphology of the samples was investigated by SEM and WAXS. The thermal behavior of the blends was analyzed by DSC. It was found that the morphology of each region depended on the composition ratio and specimen geometry. [source] | ||||||||||