断口分析中的裂纹动力学和瓦纳线实例

Case of Crack Dynamics and Wallner Line in Fracture Analysis

在为材质42CrMo钢经锻造、调质和渗氮处理的曲轴断裂断口进行失效分析的案例中,发现断口上的贝纹线有相交的异常现象;这在一般的断口中是不可能出现的。用裂纹动力学和瓦纳线的理论对这种异常现象做了分析:由断口疲劳源处产生的裂纹,在扩展时会在材料中产生应力波,在裂纹所在的表面上传播。当裂纹遇到了不连续面,就会产生了一个横向的应力波,从而形成第二组以波源为圆心的同心圆弧,这才有可能出现贝纹线相交的现象。首次观察到瓦纳线不仅仅只能在金属与非金属脆性材料的断口上出现,文中以实例说明,在调质钢的断口上也可以出现瓦纳线。

In the case of failure analysis of fracture of crankshaft with material 42CrMo,forged,tempered and nitriding treatment,it is found that there is an abnormal phenomenon of intersection of the scallop lines on the fracture surface.This is not possible in the general fracture surface.The crack dynamics and the theory of Wallner line are used to analyze the abnormal phenomenon,the crack at the source of fracture fatigue will pro duce stress wave in the material and propagate on the surface where the crack is located.When the crack en counters a discontinuous surface,a transverse stress wave is generated,thus forming a second set of concentric arcs centered at the wave source.This makes it possible for the shellfish lines to intersect.For the first time,it is observed that Wallner line cannot only appear on fracture surfaces of metallic and non-metallic brittle materials.It illustrates that Wallner line can also appear on the fracture surface of quenched and tempered steel.