接触荷重に対するセラミックスの強度とばらつき特性

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Ceramics of typical brittle material can not relieve even the extremely concentrated stress such as Hertz contact stress though local plastic deformation. And so the ceramic fracture is occurred from even comparative small microscopic defect. Using ceramics for structure combined with some components, extremely high contact stress is used to generate in the ceramics contacted locally with other components. Hertz contact stress of ceramics subjected to contact load have extremely concentrated stress distribution but is very higher in fracture strength bending or tensile fracture strength by the method of standard tests. Due to occurrence of high contact stress, ring crack is generated at contact boundary. On considering the ring crack stress to evaluate the ceramic allowable strength against contact load, the ceramic strength must not be judged from the strength gotten by bending or tensile test. This ring crack initiation strengths are governed only by extremely small defects exiting within the extremely narrow contact stress field in ceramics. Therefore, stress intensity factor K_I must be used for evaluating the fracture criteria of ceramics because of requiring to consider not only stress distribution but also defect size within contact stress field. The ceramic fracture occurs under condition of K_I ≩K_<IC>. On the other hand, the distribution of K_I indicates maximum value at the radius direction position of about r/a=1.2 outside of contact boundary:r=a. Both of defect sizes and ring crack initiating positions disperse generally and so ring crack initiating strengths estimated from K_I ≩K_<IC> also, disperse inevitably. However the dispersions are very small owing to extremely narrow extent of defect sizes relating to ring crack initiation and indicate Weibull distribution with extremely large shape parameter m and scale parameter σ_0 compared with usual strength by standard bending or tensile tests. This study could make clear of ring crack initiation mechanism and ring crack strength properties by probabilistic simulation analysis against the contact model combined a ceramic ball and a ceramic plate.
社団法人日本材料学会の論文
1998-12-15

接触荷重に対するセラミックスの強度とばらつき特性

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