利用扫描电镜对两种高强钢的疲劳断口进行了观察,并参照裂纹扩展速率曲线(log da/dN-log△K)进行了分析,其结果如下: (1)在对应低速率区的断口表面存在三个特征形貌区,这表明在该区的裂纹扩展过程具有三个阶段:裂纹形成,微裂纹扩展,和一个受沿晶开裂机制和穿晶疲劳条纹生长机制所控制的过渡阶段. (2)在中速率区,疲劳裂纹扩展的发生主要是受疲劳条纹生长机制作用.但是,发现疲劳条纹间距S并不与宏观裂纹扩展速率dα/dN相一致. (3)在高速率区,裂纹扩展速率行为是由疲劳条纹生长机制和韧窝机制所控制.有关这两种机制的相互作用和韧窝生长规律都进行了定量研究.
The fatigue fracture surfaces in specimens of two high strength steels havebeen examined by SEM nd discussed in terms of the propagation rate curve(log da/dN vs logΔK) of fatigue cracking. The results btained are as follows: (1) Fracture surfaces corresponding to the lower growth-rate exhibit three dis-tinctive zones of different appearance, showing that the propagation of cracks inthis region consists f hree stages, i.e. crack initiation, crack propagation, and atransition stage which dominated by both ransgranular striation growth and in-tergranular fracturing mechanisms. (2) In the intermediate growth-rate egion the propagation of fatigue cracksprincipally takes place by a striation mechanism, though the triation space (S) doesnot coincide with the macrocrack propagation rate (da/dN). (3) In the high rowth-rate region the rate propagation of fatigue cracks isgoverned by the striation growth mechanism as ell as by the dimple mechanism.The interaction between these two mechanisms and the pattern of the growth fdimples have been investigated quantitatively.
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