表面疲劳裂纹扩展的三维效应

THREE-DIMENSIONAL EFFECT OF SURFACE FATIGUE CRACK PROPAGATION

以拉伸圆杆为例 ,阐述表面疲劳裂纹扩展中的三维效应及其特点。利用最新的三维断裂力学成果给出一种考虑表面疲劳裂纹扩展三维效应的具体方法 ,通过该方法可以得到考虑三维应力状态的材料da dN—ΔKeff曲线。以2 0CrMo钢为例 ,处理获得 2 0CrMo材料的da dN—ΔKeff基线 ,以此对圆杆表面疲劳裂纹的扩展进行预测分析。分析结果表明 ,使用该方法以及来自标准穿透裂纹试件的材料da dN—ΔK数据可准确地预测圆杆表面疲劳裂纹的扩展寿命。该方法还可用于其他复杂结构的疲劳裂纹扩展分析。

With tensile round rob as a typical instance, the three-dimensional geometry effects and its characteristics of surface fatigue crack propagation are discussed and investigated. Using the latest achievement of three-dimensional fracture mechanics, a new practical method, which can also be used to obtain the geometry independent material base curve of d a /d N -Δ K _ eff ,is developed to eliminate the three-dimensional effects on fatigue crack growth. As a example, 20CrMo steel base curve of d a /d N -Δ K _ eff is obtained and fatigue crack propagation life of 20CrMo steel bar with elliptic surface crack is predicated in the paper. It is demonstrated that the three-dimensional geometry effects of surface fatigue crack growth can been eliminated greatly by use of the method, and surface crack propagation life in 20CrMo steel bar can be predicted accurately by use of the method in addition to fatigue crack growth data from standard through-thickness cracked specimens. The three-dimensional method can also be used to other complicated structures.