中低强度钢的da/dN的研究

THE da/dN CURVES FOR MEDIUM AND LOW STRENGTH STEELS

主要讨论了三种中低强度钢的裂纹扩展速率da dN方程 ,一般常用Paris公式。虽然该公式的通用性较好 ,但也有一定的缺陷 ,因为其常数C、n会随应力比R等参数的变化而变化。本文提出一个修正方法。实验表明 ,在不同的应力比下 ,lgda dN—lgΔK关系图上得到的各直线的斜率相近 ,裂纹扩展速率随应力比的增加而增加 ;因此 ,在Paris公式的基础上 ,加上一个影响因子 (a -R) b,对于屈服强度σs 较低的材料 ,能较明显地提高裂纹扩展速率方程的相关系数。

The cracks growth rate equations for 3 different medium and low strength steels are mainly discussed here, in which we can usually use Paris equation. Although the equation can be applied for cracks growth of various materials it has some defects, because its parameters C, N will change according to stress scales. We bring up a modificatory equation of Paris equation. The result of experiments shows: in various stress scales the slopes of lines in lg d a /d N -lg Δ K figure is very similar to each other. With the increasing of the stress scale the cracks growth rate will increase. As a result, we can add an affect factor (a-R) b on the basis of Paris equation. The new equation will distinctly raise the correlativity of cracks growth data for low strength steels. In addition we have discussed the condition for applying Paris equation and how to account for the effect of R .