Yttrium-Gadolinium-Aluminum-Iron Garnets," J . Appl. Phys., G. R IIarrison and L. R. Hodges, Jr., "Temperature Stable Effect 01 Yolyaxial Stress States on Failure Strength of Alumina Ceramics 519 E. A. Maguire and J. J. Green, "Magnetic Properties of M. A. Gilleo and S. Geller, "Magnetic and Crystallographic Properties of Substituted Yttrium-Iron Garnct, 3YL03. xM203 .-(56-x)Fez03," Phys. Rev., 110 [l] 73-78 (1958).The effect of polyaxial stress fields on the brittle fracture strength of polycrystalline alumina was investigated through the use of thin-walled cylinders. Combinations of internal pressure, external pressure, and axial loads produced stress states of tension-compression, tensiontension, and compression-compression. The failure envelope was generated for these stress states. The results indicated that biaxial tensile stresses reduced the strength of the material; however, the tensile strength increased at least 50% when a compressive stress existed normal to the tensile direction. Compression strengths as high as 640,000 psi were measured for a biaxial compressive stress state.
I. IntroductionATA and theories for brittle materials in polyaxial states D of stress are vitally important. T o conceive of an operational structure in which a simple state of stress can be postulated, let alone observed in practice, is almost impossible. This investigation was designed to measure the effects of polyaxial stresses on the fracture behavior of polycrystalline alumina. * Experimental fracture data were taken for several ratios of biaxiality, and an effort was made t o correlate these data with existing theory.A thin-walled cylinder was chosen for experimental determination of t h e failure strength envelope for alumina. Every combination of stress state could be created in this single
This paper gives a discussion of the use of the split-Hopkinson bar with particular reference to the requirements of materials modelling at QinetiQ. This is to deploy validated material models for numerical simulations that are physically based and have as little characterization overhead as possible. In order to have confidence that the models have a wide range of applicability, this means, at most, characterizing the models at low rate and then validating them at high rate. The split Hopkinson pressure bar (SHPB) is ideal for this purpose. It is also a very useful tool for analysing material behaviour under non-shock wave loading. This means understanding the output of the test and developing techniques for reliable comparison of simulations with SHPB data. For materials other than metals comparison with an output stress
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strain curve is not sufficient as the assumptions built into the classical analysis are generally violated. The method described in this paper compares the simulations with as much validation data as can be derived from deployed instrumentation including the raw strain gauge data on the input and output bars, which avoids any assumptions about stress equilibrium. One has to take into account Pochhammer–Chree oscillations and their effect on the specimen and recognize that this is itself also a valuable validation test of the material model.
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