Study on the High Temperature Strength of Ceramics and Ceramics Coating Materials Using Laser Speckle Strain/Displacement Gage

在这项研究中，疲劳裂纹扩展试验氧化铝陶瓷和氮化硅陶瓷在室温和高温下进行。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。裂纹扩展试验结果表明：1.两种材料的裂纹扩展速率随着裂纹的进一步扩展而逐渐减小，在一定的扩展量后，裂纹会暂时停止扩展; 2.裂纹扩展量与应力强度因子K的关系表明，裂纹张开度Kop随循环次数的增加而增加。在这些曲线中还观察到稍宽的滞后。这些滞后被认为是对应于颗粒桥接的裂纹张开行为的影响。随着循环次数的增加，样品的顺应性呈不连续变化。 ...更多信息 ack arresting所提到的，以及与裂纹尖端附近的颗粒桥接效应的存在有关的柔度的变化。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。结果表明：1.在相同温度下，喷砂试样的疲劳极限高于退火试样，而氧化铝涂层试样的疲劳极限低于喷砂试样; 2.陶瓷涂层试样在较高的应力水平下，虽然在疲劳寿命的早期表现出弹性变形，在疲劳寿命的中间阶段，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。在较低的应力水平下，试样在初始阶段处于弹性状态，并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

In this study, fatigue 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 concerned with the crack growth tests are as 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 for both ceramics materials.2.It was found from the relationship between COD and stress intensity factor, K,that a crack opening level, Kop, increased with increasing the number of cycles. A little bit wide hysteresis was also observed in these curves. These hysteresis were thought to correspond with the effect of particle bridging on the crack opening behavior. Furthermore, the compliance of sample varied discontinuously with increasing the number of cycles.3.Both the cr … More ack arrest mentioned the above and the variation on the compliance related to the existence of the particle bridging effect 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 that 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 increasing 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