Quantitative analysis fatigue fracture surfaces under Mode II and III and its application to tribology problems

采用自行设计的试验系统，测定了不同材料的Ⅱ型疲劳裂纹扩展速率和Ⅱ型门槛应力强度因子范围，分析了炼钢支承辊剥落失效中的裂纹：BUR主要以Ⅱ型扩展。试样的II型疲劳裂纹断口形貌与实际BUR非常相似。根据断裂力学理论，利用实验室测试的BUR的Δ K &lt;II^ &gt;数据，研究了BUR断裂后的裂纹扩展行为<th>。研究了0.47%碳钢在Ⅱ型和Ⅲ型载荷下的疲劳裂纹扩展行为。无论是Ⅱ型还是Ⅲ型剪切裂纹，在裂纹扩展过程中，裂纹尖端都发生了显微组织的变化。据推测，模式II和模式III的裂纹扩展机制基本上是相同的。

Mode II fatigue crack growth rate and Mode II threshold stress intensity factor range for the various materials were measured by using the newly developed testing system designed by head investigator.The crack in spalling failure of steel making backup rolls : BUR propagates mostly in Mode II. The Mode II fatigue crack fracture surface morphology of the specimen was very similar to that of an actual BUR. The crack growth behavior of the fractured BUR was investigated based on fracture mechanics by using the laboratory test data of Δ K_<II^<th>> for the BUR. The analysis showed the guideline to prevent the spalling of the BUR in designing process.The fatigue crack growth behavior under mode II and III loadings was studied on a 0.47 % carbon steel. Change in microstructure occurred at the crack tip in the process of crack growth both in mode II and III shear cracks. It is presumed that the crack growth mechanism of the mode II and that of the mode III are essentially the same.