弹塑性材料裂纹扩展的动态J阻力曲线实验研究简介

BRIEF INTRODUCTION OF EXPERIMENTAL STUDY ON THE DYNAMIC J-RESISTANCE CURVE OF CRACK GROWTH OF ELASTIC-PLASTIC MATERIAL

为得到弹塑性材料裂纹扩展的阻力曲线 ,采用较大外径和较大韧带直径的周边切口短圆柱小试件 ,在自行研制的间接杆—杆型冲击拉伸试验装置上进行动态断裂和起裂止裂试验。采用数值分析提出的修正方法得到韧带面上的载荷 ,结合测得的裂纹嘴张开位移 (crackmouthopeningdisplacement,CMOD) ,推广Rice远场J积分公式来计算动态J积分 ;依据柔度变化率法确定起裂点 ,获得动态起裂韧度JⅠD。利用柔度标定法得到裂纹扩展轨迹 ;提出周边切口拉伸试件裂纹扩展阻力的动态 ^JM(t)积分表征的修正形式 ,从而得到弹塑性材料裂纹扩展至止裂前的阻力曲线 ,并对相关问题进行讨论。试验结果表明 ,修正后的 ^JM(t)可以作为裂纹扩展阻力的表征参量 ,不仅适用稳态扩展过程 ,对裂纹扩展较大时也是适用的 ;对弹塑性材料裂纹扩展阻力曲线是唯一的 。

To obtain the resistance curve of crack growth of elastic-plastic material, the test about dynamic crack initiation and arrestment is carried out on a self-designed bar-bar tensile impact apparatus by using short specimens with deep circumferential notch and larger ligament diameter. Dynamic J-integral is calculated by extending the J-integral formula of Rice and using the load on ligament plane and the crack mouth opening displacement(CMOD) through direct measuring, the load is obtained by using the modified method which is proposed by previous finite element analysis(FEA) work. The time of crack initiation is determined by the compliance changing method, and corresponding dynamic crack initiation toughness J_(ⅠD) is obtained. Crack growth path is determined by the calibration curve method. The modified formula of crack growth _M(t) about tensile specimen with deep circumferential notch is proposed, then the material resistance curve is obtained. Some problems related are discussed. The results show that modified _M(t) as a characteristic parameter of crack initiation and growth, is not only applicable to stable crack growth but also applicable for fast crack growth. The material resistance curve is unique and independent on crack initial lengths.