T应力对混凝土断裂参数测定有效性的影响

Effect of T-stress on validity of determination of concrete fracture parameters

对于线弹性材料,裂缝尖端平行于裂缝方向的T应力会影响裂缝的扩展方向和起裂断裂韧度,然而在混凝土类准脆性材料的断裂韧度测试中,无论是起裂断裂韧度还是失稳断裂韧度,T应力的影响却少有研究.以混凝土Ⅰ型断裂韧度测试常用的三点弯曲梁、楔入劈拉试件为对象,计算了裂缝尖端的T应力大小,并分析了其对裂缝扩展方向和断裂韧度的影响.分析计算结果表明:这些常用试件裂缝尖端的T应力相比于裂缝尖端控制因素应力强度因子K很小,不会影响裂缝扩展方向,保证了混凝土断裂失稳前一直处于Ⅰ型裂缝状态;另外,T应力对起裂断裂韧度和失稳断裂韧度的数值也不会产生影响,说明常用试件进行的混凝土断裂韧度确定方法是可靠有效的.

For linear-elastic materials, the presence of T-stress, which acts parallel to a crack, will strongly affect the fracture onset and fracture failure. For concrete-like quasi-brittle materials, however, little attention has been focused on the T-stress influence on fracture toughness, including initiation fracture toughness and unstable fracture toughness. So three-point-bending beams and wedge-splitting specimens under mode-I fracture are used to compute T-stress, and then its influences on the crack path and fracture toughness are analyzed. It is shown that T-stress for these commonly- used specimens is so small compared to its corresponding stress intensity factor K, dominant factor around the crack tip. The pre-fabricated crack propagates along the line of the initial crack, i. e. , the crack will stay under mode-I fracture. In addition, T-stress has no influence on concrete fracture toughness, which indicates the commonly-used specimens for determining concrete fracture toughness are reliable and reasonable.