研究了三种马氏体形貌和六种马氏体含量双相钢的近门槛区疲劳裂纹扩展的微观断口形貌,SEM观察表明:所有组织的近门槛区域的断口表面均有循环解理开裂特征,说明主要由Ⅱ型应力作用控制,在较高ΔK的快速扩展区,断口特征是由混合开裂方式组成,这包括循环解理小平面,两种类型的二次裂纹和辉纹等,断口表面粗糙度诱发裂纹闭合是双相钢门槛值高的一个重要原因。
SEM microfractographic observations on fatigue crack propagation in thenear-threshold region were carried out 3 morphologies of morphologies of martensite and 6 du-al phase steels containing martensite. All of them are featured by cyclic cleavage facets, i. e.,mainly controlled by action of stress type Ⅱ. In the higher △K regions, the fracture surfaces arecharacterized by mixed modes including cyclic cleavage facets, two types of secondary cracksand striations. The roughness-induced crack closures of fracture surface is attributed primarilyto extreme high fatigue threshold value.
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