T应力对光弹性条纹影响的理论分析

以裂尖弹性应力场的多参数模型为基础，研究I型、II型以及I/II混合型裂纹参数对光弹性条纹的影响. T应力的存在和符号影响着等色线条纹环的半径大小和旋转方向，对于纯I型或II型裂纹而言，条纹环的旋转角度只与T应力有关；而对于I/II混合型裂纹，条纹环旋转角度与K_{\rm I}, K_{\rm II}和T应力有关. T应力的存在使得I型裂纹在裂尖±π/3方向上出现2个各向同性点(T应力为正时),使得II型裂纹在裂尖后的裂纹面上出现1个各向同性点. 对于I/II混合型裂纹而言，当T应力为正时等倾线出现距裂尖半径不等的3个各向同性点；反之, T应力为负时在裂尖后只存在1个各向同性点，这些各向同性点分别与I型和II型裂纹情况具有相同的规律. 

THEORETICAL ANALYSIS OF T-STRESS EFFECTS ON PHOTOELASTIC FRINGE PATTERNS IN CRACKS

Based on the multi-parameter mathematic model of the elastic stress field near a crack-tip, the influences of the stress intensity factors K_{\rm I}, K_{\rm II}, and T-stress on the photoelastic isochromatic and isoclinic fringe patterns are presented for the mode I, mode II and mixed mode I/II crack, respectively. It is confirmed that T-stress influences the radius and rotate direction of the isochromatic fringe loops. The rotated angle of the loop only relates to the T-stress for the mode I or II crack, while to the intensity factors K_{\rm I}, K_{\rm II}, and T-stress for the mixed mode I/II crack. There are two isotropic points along ±π/3 directions in the mode I crack under positive T-stress, while none of isotropic point under the negative T-stress. For the mode II crack only one isotropic point appears behind the crack-tip under T-stress. For the mixed I/II crack, three isotropic points with different radius appear at the corresponding positions under the positive T-stress, however, one point exists behind the crack-tip for the negative T-stress. Thses isotropic points for the mixed I/II crack comply with rules in the mode I and mode II, respectively.