循环载荷下裂尖形变规律的实验研究

EXPERIMENTAL STUDY OF CRACK TIP DEFORMATION UNDER FATIGUE LOAD

应用散斑干涉技术，在常幅载荷下对疲劳裂纹扩展过程中的一个循环周期内，不同加载阶段的裂尖应变、裂纹张开位移进行了原位测量，给出了裂纹闭合对裂纹张开位移及裂尖形变的影响规律．结果表明：由于裂纹闭合和残余压应力的存在，疲劳裂尖应变与外加载荷的平方并不成正比．在加载初期，裂纹处于闭合状态，裂尖应变无明显变化，随着载荷的增加，裂纹逐渐由远离裂尖处张开并向裂尖发展．一旦裂纹完全张开，裂尖应变迅速增加．对裂尖应力－应变状态的分析表明，裂尖材料的应力－应变关系类似于光滑试样低周拉压疲劳应力－应变滞后关系．

The SPI technique was used to measure in situ the crack tip strain and crack opening displacement(COD) at various loading stages in one loading cycle during constant amplitude fatigue crack propagation. The influences of crack closure on crack tip strain and COD were also discussed. The results show that due to the crack closure and the residual compressive stress, the strain is not a proportional relation to the square of loading value. At the initial loading stage, the crack closed and crack tip strain was not changed obviously.With increasing load, crack was opened graduatally from a distant place towards crack tip.After crack tip was fully opened, the strain increased rapidly. The study of the stress-strain behaviour ahead of crack tip indicated that the hysteretic nature of the stress-strain behaviour of material at the crack tip is similar to that produced by low cycle and strain controlled fatigue.