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本文研究了表面椭圆形缺陷产生疲劳裂纹的规律。结果表明:具有曲率半径为ρ的表面缺陷形成裂纹的寿命N_i=A((p/△K_1)~n,A=(a(ρ~(1/2))~B。α,β,n是材料常数。不出现裂纹的门槛应力场强度因子△K_(th)和ρ有关。本文用“变载荷勾线法”研究了表面裂纹在拉伸疲劳和弯曲疲劳时裂纹扩展的规律。结果表明:拉伸疲劳时表面裂纹α向和c向扩展速率可用Paris公式描述,且和中心贯穿裂纹发展速率处在同一分散带内。三点弯曲疲劳时情况完全不同,这时用“二维法”来处理更为合适。本文也研究了表面裂纹疲劳扩展时形状变化的规律。结果表明:对三点弯曲,c/a+B/a=1士0.1(a是裂纹深度,2c是长度,B是板厚)。拉伸疲劳时a/c趋于一个稳定的值c/a=0.75士0.1。本工作表明,对浅的表面缺陷,形成宏观裂纹的寿命远比裂纹扩展到临界尺寸的寿命高。因此,对带伤构件进行寿命估算时必须考虑缺陷形成裂纹的寿命。
In this paper, the law of the fatigue cracks on the surface oval defects is studied. The results show that the lifetime of cracks with surface defects with radius ρ of curvature is N_i = A ((p / △ K_1) ~n, A = (a ρ ~ (1/2)) ~ B.α, β, Material constant.The threshold of stress field without cracking is related to △ K_ (th) and ρ.The law of crack propagation on surface crack under tensile fatigue and flexural fatigue is studied in this paper by using “variable load-line method.” The results show that: Tensile fatigue surface crack α and c expansion rate can be described by the Paris formula, and the central crack propagation rate throughout the same dispersion zone. Three-point bending fatigue when the situation is completely different, then use the “two-dimensional method” to The results show that for three-point bending, c / a + B / a = 0.1 ± 0.1 (a is the depth of the crack, 2c is the length, B is the length Plate thickness.) The tensile fatigue a / c tends to a stable value of c / a = 0.75 ± 0.1. This work shows that the shallow surface defects, the formation of macroscopic cracks far longer life than the crack to expand to the critical size Therefore, the life span of defects must be taken into account when estimating life expectancy of injured components.