关键词: 港口工程, 残余应变, 断裂过程区, 三点弯曲实验, 数字图像相关技术, 循环荷载

Abstract: To investigate the crack propagation rule and failure mechanism of concrete under cyclic loading, digital image correlation (DIC) technology was employed to analyze the evolution process of the load-crack mouth opening displacement (P-CMOD) curve. The variation characteristics of the crack mouth opening displacement (CMOD), crack length (a) and the residual strain in the fracture process zone, over the number of cycles and the unloading position, were quantitatively analyzed. The research results indicate that under constant-amplitude cyclic loading, the evolution of CMOD exhibits a three-stage characteristic: rapid accumulation, linear growth, and instability leading to failure. The crack length (a) is highly correlated with the changes of CMOD. At a stress level of 0.4 Fmax, a exhibits linear slow increase and then stabilizes. With increasing stress levels, a undergoes rapid extension in the early stage, followed by a deceleration in the growth rate, where residual stress promotes stable crack propagation. Under envelope cyclic loading, the growth rate of a converges while the CMOD continues to extend, indicating a gradual increase in the width of the fracture process zone. The accumulation rate of residual strain increases significantly with the load level. At 0.6 Fmax, the strain growth rate is 2.6 times that at 0.4 Fmax, and the high unloading residual stress exacerbates strain concentration. Based on the segmented mechanical response and dynamic damage evolution mechanism, a P-CMOD curve model that could predict the crack growth rate, failure critical point and response under multiple loading conditions is established, which provides a basis for the fatigue damage assessment and life prediction of concrete structures.

Key words: port engineering, residual strain, fracture process zone, three-point bending test, digital image correlation technique, cyclic loading