弹性T项对裂尖参数和裂纹扩展路径稳定性的作用

EFFECT OF THE ELASTIC-T-TERM ON THE CRACK-TIP PARAMETERS AND THE STABILITY OF CRACK GROWTH PATH

研究了弹性T项在主裂纹与近裂尖微空洞干涉问题中对裂尖参数和裂纹扩展路径稳定性的影响作用.利用“伪力”法，并通过解决主裂纹与近裂尖微空洞干涉问题，对远场纯1型载荷和远场弹性T项载荷下，该干涉问题中弹性T项的影响作用进行了分析从数值结果可以看出：由于空洞的存在；释放了弹性T项所引起的应力，弹性T项对裂尖参数；应力强度因子和J积分都有直接显著的影响，因而，它对该载荷下的裂纹扩展路径的稳定性有控制作用。

The so-called elastic T-term is the third term of Williams expansion for the linear elastic crack tip field, which is constant along the crack plane over a large distance in front of or behind the crack tip and has been introduced as an another independent crack tip parameter. It was shown that the T-stress has no direct effect on the crack tip parameters, such as the J-integral,in linear deviation. However, the T-stress influences significantly the shape and size of the plastic zone under the small-scale yielding condition. In this way, it affects indirectly on the J-integral. In this paper, the effect of the elastic-T-term on the crack-tip parameters, such as the stress intensity factors, the J-integral, and the stability of crack growth path is studied by considering microvoid in the near tip stress fields. By using the 'pseudo-traction' method and the superposition technique,the interaction problem between macrocrack with a microvoid is reduced into a Fredholm integral equations which can be solved numerically by using the Chebyshev numerical integral method.Several numerical results are given in figures from which it is found that the T-term has direct and important effect on the oracle tip fracture parameters, such as the stress intensity factors, the J-integral. Furthermore, the effect of the T-term depends on the values of the T-term and the location of the microvoid, which is mainly because that the microvoid not only releases of the near-tip residual stresses induced by remote loading and the T-term loading but also decreases the effective elastic moduli near the macrocrack tip. Another important effect of the T-term is that it influences significantly the rate between the Mode I stress intensity and the Model II stress intensity, . Thereby, the T-term has effect on the crack expansion angle and the stability of crack growth path in the present interaction problem according the maximum hoop stress criterion.From the numerical results given in this paper, it can be concluded that the positive elastic-T-term leads to decreasing the stability of the crack growth path, while the negative elastic-T-term leads to increasing the stability. The phenomenon of the T-term effect observed in this interaction problem is similar to that shown by Cotterell and Rice in single slightly curved or kinked crack problem.