Analysis Of The Collective Evolution Of High Temperature Low-cycle Short Fatigue Crack Under Complex Stress Condition

Though the macro fracture mechanics has been successfully applied in many fields, the theory can not be employed to deal with short cracks for the randomicity of progression rate of the short cracks. At present, the study of short cracks is far from practical usage, especially the study of collective evolution of high temperature low-cycle short fatigue crack under complex stress condition is still a blank field.The 16MnR cylindrical specimens with circle indentation were employed in the low cycle short cracks fatigue tests under 400℃. To obtain data of the fatigue short cracks progression in large extent, specimens with different circle indentation gauge were tested and different load condition was applied. Through test interruption and copy-surface method, tests were conducted to observe and analyse the initiation and propagation process of short cracks with metallographic microscope.The cracks observed in the tests are of 'Z' shape when in their minor size. The results of the tests indicate that the spots where the fatigue short cracks initiated are at the bottom surface of the circle indention and some disfigurement places in that surface. The propagation paths of the cracks are very complex and the decentralization of the obtained data is very severe due to the micro organism of the material. While the distribution of the short fatigue cracks exist self-regularity on their length, angle, density and expansion rate of the cracks, which are less affected by the outer factors.