时新红，张建宇，肖青山，费斌军

 

北京航空航天大学  固体力学研究所，北京 100191

 

　　摘要：对航空常用铝合金不同轴向平均应力下拉扭比例加载疲劳失效典型断口进行了宏观及微观分析。通过对典型断口的宏观分析，得到比例加载下多轴疲劳裂纹萌生与扩展的平面和方向；通过对典型断口的微观分析，得到疲劳源区、扩展区及瞬断区的微观特征。宏观分析的结果表明，拉扭比例加载下，最大剪应力幅和法向平均应力对裂纹萌生和扩展的方向有一定的影响，疲劳裂纹的萌生和扩展平面均接近最大剪应力幅值所在的平面，随着平均应力值的增大，较多的裂纹倾向于在有着较大法向平均应力的最大剪应力幅平面内萌生和扩展，并且偏离最大剪应力幅平面的角度值在增加。微观分析的结果表明，随着轴向平均应力值的增加，疲劳源区裂纹源数目增加，台阶特征也变得不明显，扩展区的疲劳条带特征越来越不明显，瞬断区的等轴韧窝越来越多。

 

　　关键词：多轴疲劳，轴向平均应力，铝合金

 

　　Studies On Crack Initiation And Growth Of Mutiaxial Fatigue Under Different Axial Mean Stress

 

　　Shihongxin,Zhangjianyu,Xiaoqingshan,Feibinjun

 

　　Beijing University of Aeronautics & AstronauticsResearch Institute of solid mechanics Beijing 100191

 

　　Abstract:Macro-analysis and micro-analysis of aluminum alloy fracture appearance were conducted for different mean tensile stress under in-phase axial-torsional loadings. Macro-analysis of fracture appearance was carried out in order to obtain the planes and orientations of crack initiation and propagation, and micro-analysis of fracture appearance was carried out in order to obtain the micro features of origin region, extension region and final rupture region under in-phase axial-torsional loadings. The results of macro-analysis show that both the maximum shear stress amplitude and normal mean stress have effects on the orientations of crack initiation and propagation, and the orientations of fatigue crack initiation and propagation are close to the plane of the maximum shear stress amplitude plane. More cracks are inclined to initial and propagate on or near the maximum shear stress amplitude plane that had the larger normal mean stress with increasing the mean tensile stress, and the angle of deviation from the plane of maximum shear stress amplitude increases. The results of micro-analysis show that with increasing the mean tensile stress, the step-like characteristic become not evident in the origin region, fatigue fringe become not remarkable in the extension region and equiaxed dimples become more significant in the final rupture region.

 

　　Key words:multiaxial fatigue, axial mean stress, aluminum alloy

 

　　联系方式

 

　　时新红：shixinhong@buaa.edu.cn