小尺寸混凝土试件双K断裂参数试验研究

EXPERIMENTAL INVESTIGATION ON DOUBLE-K FRACTURE PARAMETERS FOR SMALL SIZE SPECIMENS OF CONCRETE

采用最大尺寸为680mm×160mm×40mm的标准三点弯曲梁试件,利用在初始裂缝两侧粘贴电阻应变片并利用混凝土裂缝扩展到此处时其应变回缩的方法测得了起裂荷载Pini,在此基础上根据Pini及初始缝长a0得到了起裂断裂韧度KIiCni;根据在试验中测得的最大荷载Pmax及对应的裂缝口张开位移CMODC计算了混凝土等效裂缝长度aC,据此计算了失稳断裂韧度KIuCn。结果表明:采用电阻应变片法可准确测定混凝土的起裂荷载Pini,且方法简单。试验结果还表明:在本试验范围内,三点弯曲梁法测得的混凝土双K断裂参数KIiCni、KIuCn与试件高度无关,进一步说明了混凝土双K断裂参数可以作为描述混凝土裂缝扩展的断裂参数。

Strain gauges are adhered to the tip of the pre-cracks on three-point bending beams, whose maximum size is 680mm×160mm×40mm. The initial load Pini can be measured according to the sudden decrease of stain gauges＇ values. Then initial fracture toughness can be obtained using Pini and initial crack length a0. Moreover, critical crack length can be obtained by means of the maximum load Pmax and the corresponding crack mouth opening displacement CMODc from test. The experimental results show that it is simple and effective to measure the initial load of concrete using strain gauges. The results also indicate that the measured double-K fracture parameters, KIC^ini, KIV^un, based on three-point bending beams, are independent of specimens size. Hence, double-K fracture parameters can be viewed as the criterion to predict or estimate crack development.