Development of Optimum Proof Testing Method of Structural Ceramics

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The aim of this research is to develop the optimum method of proof testing of structural ceramics. The optimum method implies such a method by which the highest probability of surviving proof testing is attained under the condition that S_<fmin>*S_d, where S_<fmin> is the minimum strength after proof testing and S_d is the required strength. The principal results of the research are summarized as follows.1. The optimum proof testing method was first studied for the case of uniform stress distribution. It was found that the optimum testing method is to use the maximum unloading rate available and the test load which satisfies S_<fmin>=S_d under this unloading rate.2. The optimum proof testing method was then studied for the case of non-uniform stress distribution. This case Is Important as real machine components are generally subjected to non-uniformly distributed stresses. It was found that the optimum testing method is to use the maximum unloading rate available and the test load whi … More ch satisfies S_<fmin>=S_d at the point of the maximum stress in the component.3. The influence of the K-V relation on the effect of proof testing was studied by means of computer simulation, where K is the stress intensity factor and V=da/dt is the stable crack growth rate. It was found that when the unloading rate is larger than the critical unloading rate, exterpolation of the first region's K-V relation to the second and third regions does not result in substantial error in calculation of the minimum strength after proof testing and the probability of surviving the proof test.4. A method for estimating the critical unloading rate was proposed, and the usefulness of this method was demonstrated experimentally.5. For application of proof testing to ceramic bearing balls, the statistical properties of the ring crack initiation strength and the final fracture strength under crushing load were clarified experimentally. Furthermore, a probabilistic theory for interpreting the experimental results was proposed.6. Proof testing of Si_3N_4 bearing balls was conducted and importance of unloading rate was demonstrated experimentally. Less