![]() ![]() The impact of this damage on material performance was limited to the matrix dominated properties only. The results showed that for the most severe conditions examined that only surface matrix fracture was present with no observable fiber fracture. This temperature change was varied in severity (magnitude) and in number of shocks applied to a given sample. Thermal shock resistance for the two material systems was determined experimentally by subjecting plates to sudden changes in temperature on one surface while maintaining the opposite surface at a constant temperature. ![]() Using a simple maximum stress criteria for each constituent, it was observed that fiber fracture would occur only at the most extreme thermal shock conditions and that matrix fracture, splitting parallel to the reinforcing fiber, was to be expected for most practical cases. The effect of various material parameters, including thermal conductivity, elastic modulus, and thermal expansion, were examined analytically for their effect on thermal shock performance. The analytical investigation focused on the development of simple expressions for transient thermal stresses induced during thermal shock. The program was divided into three technical tasks baseline mechanical properties, thermal shock modeling, and thermal shock testing. The composite systems examined were oxide-based, consisting of an aluminosilicate matrix with either polycrystalline aluminosilicate or single crystal alumina fiber reinforcement. The experimental and analytical investigation of the thermal shock phenomena in ceramic matrix composites is detailed. Thermal shock resistance of ceramic matrix composites Good agreement is found between experimental results and theoretical predictions of failure probability as a function of time and initial specimen temperature. Material strength parameters are determined using concentric ring flexure tests. Experimental results are compared with theoretical predictions based on a finite-element method thermal stress analysis combined with a statistical model of fracture. The technique is demonstrated with soda-lime glass specimens. Transient specimen temperature and acoustic emission are monitored continuously during the thermal stress cycle. Uniform equibiaxial tensile stresses are induced in the center of the test specimen. In contrast with traditional techniques, the well-defined thermal boundary condition allows for accurate analyses of heat transfer, stress, and fracture. The technique employs contact between a metal-cooling rod and hot disk-shaped specimen. The sensitivity of helium leak rate measurements was improved up to 70 percent by baking headers for two hours at 200 C after thermal shocking.Ī novel quantitative thermal shock test of ceramics is described. Both header types passed thermal shock tests to temperature differentials of 646 C. Headers manufactured in cryogenic nitrogen based and exothermically generated atmospheres showed differences in as-received leak rates, residual oxide depths and pin glass interfacial strengths these were caused by the different manufacturing methods, in particular, by the chemically etched pins used by one manufacturer. A 'critical stress resistance temperature' was not exhibited by the 14 pin Dual In-line Package (DIP) headers evaluated. ![]() Pin-pull tests used to compare the interfacial pin glass strengths showed no differences between thermal shocked and not- thermal shocked headers. Thermal shocking was shown to be not destructive to highly reliable glass seals. Tests were performed to determine if thermal shocking is destructive to glass-to-metal seal microelectronic packages and if thermal shock step stressing can compare package reliabilities. Thermal shock testing for assuring reliability of glass-sealed microelectronic packages The test and analysis algorithm show promise as a means to characterize thermal shock strength of ceramic materials. An uncensored thermal-shock strength Weibull distribution is then determined. The surface temperature distribution for each test and AlN's thermal expansion are used as input in a finite-element model to determine the thermal-shock strength for each specimen. Aluminum nitride (AlN) substrates are thermally shocked to fracture to demonstrate the technique. Ferber, M.K.Ī thermal-shock strength- testing technique has been developed that uses a high-resolution, high-temperature infrared camera to capture a specimen's surface temperature distribution at fracture. Probabilistic thermal-shock strength testing using infrared imaging ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |