残余应力场中疲劳裂纹的闭合作用

CLOSURE EFFECT OF FATIGUE CRACK IN RESIDUAL STRESS FIELD

疲劳裂纹在残余压应力场中的扩展可藉助于裂纹闭合力来描述。采用板状试样相变温度下急冷以获得长程残余压应力场。应用动态测定法可同时测得裂纹闭合力和扩展速率。结果表明,残余压应力的最大值位置与扩展速率的最低值和闭合力的峰值所对应的裂纹长度基本相同。可以认为残余压应力提高了裂纹的闭合力,它使最小有效应力强度因子 K_(eff min)升高,从而减小了裂纹的扩展驱动力△K_(eff),这是裂纹扩展速率降低的主要原因。

Fatigue crack propagation in a compressive residual stress field can be char-acterized with the closure effect.The closure force under cyclic loading as well as crackgrowth rate may be determined by experiments.Results show that the minimun crackgrowth rate appears at the maxium value of closure force and agrees with the peak locationof compressive residual stress.It confirms that the higher the compressive residual stress thelarger the closure force,thus it results in the increase of K_(eff min),decrease ofΔK_(eff),andlowers the crack growth rate.