Study on Fatigue Strength of Ceramics and Ceramics Coating Materials Using Laser Aided Strain Monitoring Technique

本文研究了陶瓷和陶瓷涂层材料的疲劳强度。在室温和高温下对氧化铝陶瓷和氮化硅陶瓷进行了裂纹扩展试验。在试验过程中还测量了裂纹张开位移。利用这些实验数据对陶瓷材料的裂纹扩展特性进行了讨论。研究结果如下：1.随着裂纹的进一步扩展，裂纹扩展速率逐渐减小，在裂纹扩展一定时间后，两种陶瓷材料的裂纹都暂时停止扩展.从裂纹张开位移与应力强度因子的关系可知，裂纹张开度Kop随着循环次数的增加而增加。在这些关系中也观察到了一个有点宽的滞后。这些滞后被认为是对应于粒子桥接的裂纹张开行为的影响。此外，S 关于我们 在疲劳试验过程中，样本不连续变化。裂纹的止裂和柔度的变化都与裂纹尖端附近的颗粒桥接有关。裂纹尖端的应力强度因子可以通过减去桥接效应引起的摩擦应力而降低。其次，对陶瓷涂层材料进行了室温和高温疲劳试验。涂层材料的结果如下：1.虽然在室温下喷砂的样品比在相同温度下退火的样品具有更高的疲劳极限，但氧化铝涂层样品的疲劳极限比喷砂样品低。虽然陶瓷涂层样品在较高的施加应力水平下的疲劳寿命的早期阶段显示出弹性变形，但在疲劳寿命的中期阶段，塑性变形随着循环次数的增加而增加。这一现象与基材的循环软化行为相一致。在疲劳寿命的最后阶段，样品的表面应变不连续地变化。这意味着由于涂层材料和基材之间的分层而出现无应变的区域。在较低的外加应力水平下，试样早期处于弹性状态，逐渐表现出塑性变形行为。在疲劳寿命的最后阶段，随着循环次数的增加，试样的塑性应变范围减小。这意味着单个主裂纹只能在这种条件下扩展。少

Fatigue strength of ceramics and ceramics-coated materials were studied in this study. Crack growth tests for alumina ceramics and silicon nitride ceramics were performed at both room and elevated temperature. The crack opening displacement was also measured during the tests. Then the crack growth characteristics of ceramics were discussed using these experimental data. The results obtained from this study are s follows.1. The crack growth rate was found to decrease gradually with a further crack growth, and after some crack extension a crack stopped growing temporary in both ceramics materials.2. It was found from the relationship between crack opening displacement and stress intensity factor that a crack opening level, Kop, increased with increase in the number of cycles. A little bit wide hysteresis was also observed in these relations. These hysteresis were thought to correspond with the effect of the particle bridging on the crack opening behavior. Furthermore, the compliance of s … More ample varied discontinuously during a fatigue test.3. Both the crack arrest mentioned the above and the variation on the compliance related to the influence of the particle bridging near the crack tip. The stress intensity factor at crack tip was reduced by subtracting the friction stress due to this bridging effect.Next, fatigue tests for ceramics coating materials were conducted at both room and elevated temperature. The results for coating materials are as follows.1. While the blasted sample at room temperature has a higher fatigue limit than the annealed sample at the same temperature, the alumina coated sample has a lower fatigue limit than the blasted sample.2. Though the ceramics coated sample shows the elastic deformation at an early stage of fatigue life under a higher applied stress level, the plastic deformation increased with increase in the number of cycles at a middle stage of fatigue life. This behavior corresponded with the cyclic softening behavior of substrate. At a final stage of fatigue life the surface strain of the sample varied discontinuously. This means that the region with no strain due to the delamination among a coat material and a substrate appeared.3. Under a lower applied stress level, the sample was under an elastic state at an early stage, and gradually showed the plastic deformation behavior. At a final stage of fatigue life, however, the plastic strain range of sample decreased with increasing the number of cycles. This means that a single main crack can only propagate under this condition. Less