The shear fatigue delamination strength of some porous thermal barrier coatings (TBCs) has been evaluated using the torsion pin-test method. The porosities of the tested TBCs were 0-5, 5-10, 15-20 and 25-35%. The shear delamination strength of the TBCs was evaluated and the shear fatigue delamination strength ( S – N ) curves were obtained under cyclic torsional loading. The Young’s modulus of the TBCs was evaluated by using indentation tests and the corresponding numerical analyses, and expressed as a function of coating porosity. Finite element analyses, using the commercial nonlinear finite element analysis software MARC, showed that almost the same stress distributions could be observed around the interface edge between the top coat and the bond coat when delamination occurred, regardless of the pin diameter. Therefore, only the specimens of 4-mm pin diameter were used in the fatigue test. The shearing fatigue delamination strength was investigated under cyclic torsion without tension. If combined torsion and tension were applied, fracture would occur inside the top coating instead of adhesively at the bond coat interface. It was found that the normalized S – N curves, divided by the critical delamination stress due to simple torsion, coincided with each other. Next, the stress intensity factor ( K ) of the singular shear stress field around the interface edge was determined for various porous coatings under simple torsion, and the relationships between K and porosity P v were derived. The strength ( K ) of the shear stress singularity field was adopted as the fatigue delamination criterion for the porous TBCs under cyclic shearing. Finally, the S – N curves could be determined for porous TBCs with any value of porosity.

中文翻译：

---

用扭力销试验法评价多孔热障涂层的剪切疲劳分层强度

一些多孔热障涂层 (TBC) 的剪切疲劳分层强度已使用扭力销试验方法进行评估。测试的 TBC 的孔隙率为 0-5、5-10、15-20 和 25-35%。评估了 TBC 的剪切分层强度，并在循环扭转载荷下获得了剪切疲劳分层强度（ S - N ）曲线。TBC 的杨氏模量通过使用压痕测试和相应的数值分析进行评估，并表示为涂层孔隙率的函数。使用商用非线性有限元分析软件 MARC 进行的有限元分析表明，在发生分层时，在面涂层和粘合涂层之间的界面边缘附近可以观察到几乎相同的应力分布，而与销直径无关。所以，在疲劳试验中仅使用了 4 毫米直径的试样。在无张力的循环扭转下研究了剪切疲劳分层强度。如果同时施加扭力和张力，则会在面漆内部发生断裂，而不是在粘合涂层界面处发生粘合。发现归一化的 S-N 曲线除以由于简单扭转引起的临界分层应力，彼此重合。接下来，确定了各种多孔涂层在简单扭转下界面边缘周围奇异剪切应力场的应力强度因子（ K ），并导出了 K 与孔隙率 P v 之间的关系。采用剪切应力奇异场强度（K）作为多孔TBCs在循环剪切作用下的疲劳分层判据。最后，