砼断裂韧度尺寸效应的试验研究

Experimental Investigation into Size Effect of Fracture Toughness of Concrete

为研究混凝土断裂韧度的尺寸效应,将基于Weibull统计理论的尺度律与基于Bazant能量释放原理的尺度律进行对比,进行了3种混凝土断裂韧度,即起裂韧度Ki1nci、失稳韧度Ku1nc及临界裂缝尖端张开位移δc的试验研究.采用在建桥梁所用高强混凝土材料制作了6组共18根几何相似、最大尺寸为1280mm×320mm×160mm(长×高×宽)的带预制缺口的素混凝土平面应变三点弯曲试件,应用MTS材料试验机、动态应变仪等测试手段获得了试件的荷载-加载点位移、荷载-裂缝嘴张开位移的全过程曲线以及裂缝前沿应变等.计算结果表明,考虑了裂缝前沿过程区影响的混凝土断裂韧度仍然表现出一定程度的尺寸效应,而Bazant能量释放尺度律较Weibull统计理论尺度律更适用于预测大尺寸混凝土材料的断裂韧度.

In order to investigate the size effect of the fracture toughness of concrete, the size effect law deduced from Weibull＇s statistical theory was compared with that from Bazant＇s energy release principle, and three fracture parameters, namely, the initiatial fraction toughness （K1c^ini）, the unstable toughness （K1c^un） and the critical crack tip opening displacement （δc） were tested. Moreover, 18 three-point bending specimens of notched beams were fabricated and divided into 6 groups according to their geometric similarity with the maximum dimension of 1280 mm in length, 320mm in height and 163 mm in width. The full-process curves of the load-crack mouth opening displace-ment and the load-displacement at loading points, as well as the strain in front of the cracks, were obtained by using the MTS tester and the dynamic strain tester. Calculated results indicate that the fracture toughness conside-ring the influence of process zone on the crack tip exhibits a certain size effect, and that, as compared with the size effect law suggested by Weibull, the one suggested by Bazant is more suitable for the prediction of the fracture toughness of large-sized concrete.