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本文回顾了各种金属及合金在门坎区附近的疲劳裂纹扩展的机制和特徵。 根据一系列试样和结构的微观断口金相分析的结果表明,在近门坎区产生的占主导的断口形态是小平面或河流花样。对于不同金属与合金小平面的方位与晶体点阵结构的相互关系,用滑移型和层错能进行描述,在非轴向载荷下,曾提出一个更为普遍的疲劳裂纹扩展特性。 在本文中,对于板状及缺口试样的疲劳极限和门坎值的相互关系以及短裂纹的疲劳裂纹扩展机制也一起进行了评述,短裂纹的裂纹扩展行为可以一般地表达为: △K_(th)=f(a)△σ_(th)(πa)~(1/2)式中,f(a)为裂纹长度与试样几何形状的函数。 本文对应力比、显微组织、环境对在门坎区附近疲劳裂纹扩展行为的影响也进行了回顾,曾提出产生裂纹闭合效应的“氧化物诱发”及“粗糙度诱发”的概念,可以用来解释结构材料中上述因素对在近门坎区疲劳裂纹扩展行为的影响。
This paper reviews the mechanisms and characteristics of fatigue crack propagation in the vicinity of the threshold area of various metals and alloys. Based on a series of microstructure and microstructural fracture surface metallographic analysis results show that the predominant fracture morphology in the near-threshold area is a facet or river pattern. The relationship between the orientation of the different metal and alloy facets and the lattice structure of the crystal is described by slip and stacking faults. A more common feature of fatigue crack growth has been proposed under non-axial loading. In this paper, the relationship between the fatigue limit and the threshold value of the plate-shaped and notched specimens and the fatigue crack growth mechanism of the short crack are also reviewed. The crack propagation behavior of the short crack can be generally expressed as: ΔK_ (th ) = f (a) Δσ_ (th) (πa) ~ (1/2) where f (a) is a function of crack length and sample geometry. In this paper, the effects of stress ratio, microstructure and environment on the fatigue crack propagation near the threshold area are also reviewed. The concepts of “oxide induced” and “roughness induced” that produce crack closure effect have been proposed Explain the influence of the above factors on the fatigue crack growth behavior near the threshold in structural materials.