Reliability Engineering. Properties of Strength and Distribution for Ceramics Subjected to Contact Load.
Reliability Engineering. Properties of Strength and Distribution for Ceramics Subjected to Contact Load.
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可靠性工程。
DOI：
10.2472/jsms.47.1251
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
Norio Kan
中科院分区：
文献类型：
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作者：
N. Okabe;Y. Abe;M. Ichikawa;Toru Takamatsu;Norio Kan
典型脆性材料的陶瓷即使发生局部塑性变形，也不能消除赫兹接触应力等极其集中的应力。因此，即使是相对较小的微观缺陷也会导致陶瓷断裂。陶瓷作为结构与某些部件结合在一起，在与其他部件局部接触时，会产生极高的接触应力。在接触载荷作用下，陶瓷的赫兹接触应力具有非常集中的应力分布，但按标准试验方法，其断裂强度、弯曲断裂强度或拉伸断裂强度都非常高。由于接触应力较大，在接触边界处产生环状裂纹。在考虑环裂纹应力来评估陶瓷在接触载荷作用下的许用强度时，不能用弯曲或拉伸试验得到的强度来判断陶瓷的强度。这种环形裂纹的萌生强度仅由陶瓷中极窄的接触应力场中存在的极小缺陷决定。因此，在评价陶瓷的断裂判据时，不仅要考虑接触应力场内的应力分布，还要考虑接触应力场中的缺陷尺寸，因此必须用应力强度因子KI来评价陶瓷的断裂准则。陶瓷断裂是在KI≥KIC条件下发生的。另一方面，KI的分布在接触边界外的半径方向位置r/a=1.2时出现极大值：R=a，缺陷尺寸和环状裂纹萌生位置普遍分散，因此由KI≥KIc估算的环状裂纹萌生强度也不可避免地分散。然而，由于与环状裂纹萌生有关的缺陷尺寸范围非常窄，弥散很小，并且与标准弯曲或拉伸试验的常规强度相比，形状参数m和尺度参数σ0都非常大的威布尔分布。通过对陶瓷球和陶瓷板的接触模型进行概率模拟分析，可以明确环裂纹的萌生机理和强度特性。
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 KI 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 KI≥KIC. On the other hand, the distribution of KI 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 KI≥KIC, 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 σ0 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.