非标准混凝土三点弯曲梁双K断裂韧度试验研究

Experimental research on double-K fracture toughness of non-standard three point bending concrete beam

采用跨度和初始缝高比恒定的非标准混凝土三点弯曲梁试件,以双K断裂理论为基础,根据改进的断裂韧度计算方法,通过试验实测试件的荷载与裂缝张口位移全过程曲线,计算不同初始裂缝长度和不同试件截面高度的非标准混凝土三点弯曲梁试件的有效裂缝长度ac、起裂断裂韧度KIinCi和失稳断裂韧度KuICn。试验结果表明:非标准混凝土三点弯曲梁试件的起裂荷载Fini、最大荷载Fun以及有效裂缝长度ac均随跨高比的减小而增大;裂缝亚临界扩展量Δac、起裂断裂韧度KIinCi和失稳断裂韧度KuICn均与跨高比无关,在试验设计的试件截面高度下为一个常数。

Through the testing of non-standard three-point bending concrete beam specimens with the same span and initial crack-depth ratios and the modified computing methods of fracture toughness based on double-K fracture theory, complete load and the corresponding crack mouth opening displacement curves were measured in the experiment. The critical effective crack length ao , initial fracture toughness KIinCi and the unstable fracture toughness KIinCi for the non-standard three point bending beams with different initial crack lengths and different specimen heights were determined. The results indicate that the initial load Fini , the maximum load Fun and the critical effective crack length ac will increase along with the decrease of the span-depth ratio. The precritical crack propagation length △ac , the initial fracture toughness KIinCi and the unstable fracture toughness KIinCi are independent of the span-depth ratio, which can be considered as a constant for concrete materials for the test design.