中文摘要：

针对混凝土I型裂缝扩展问题,分别采用以起裂韧度为参数的裂缝扩展准则、最大拉应力准则以及裂尖处应力强度因子为零的裂缝扩展准则,数值模拟了强度等级C20、C40、C60、C80和C100的混凝土三点弯曲梁裂缝扩展全过程,获取了试件的荷载-裂缝口张开位移（P-CMOD）曲线并与试验结果进行了比较。结果表明,三种准则中以起裂韧度为参数的裂缝扩展准则计算得到的峰值荷载及P-CMOD全曲线与试验结果差别最小。随着混凝土强度等级的提高,最大拉应力准则以及裂尖处应力强度因子为零的裂缝扩展准则计算出的P-CMOD曲线与试验结果相比均有较为明显的偏离,但以起裂韧度为参数的裂缝扩展准则计算结果与试验曲线更为吻合。试验与计算结果表明,以起裂韧度为参数的裂缝扩展准则更适用于不同强度混凝土材料的断裂分析。

英文摘要：

In order to analyze the propagation of concrete mode Ⅰ crack, three crack propagation criteria, which are characterized by the initial fracture toughness, maximum tensile stress and nil stress intensity factor at the tip of the crack, are introduced to derive the load-crack mouth opening displacement curves（P-CMOD） of three-point bending beams. The P-CMOD curves are compared with the experimental results of concrete with variated strength including C20, C40, C60, C80 and C100. The results indicate that the peak load and the P-CMOD curves calculated using the crack propagation criterion characterized by initial fracture toughness have best matched with the experimental ones. With the increasing of concrete strength, the P-CMOD curves calculated by the crack propagation criteria characterized by maximum tensile stress and nil stress intensity factor at the tip of the crack show an obvious deviation from the experimental curves; while the P-CMOD curves calculated by the crack propagation criterion characterized by initial fracture toughness are close to the experimental results. It is indicated that the crack propagation criterion characterized by initial fracture toughness is more suitable to analyze the fracture process of concrete beams with different strength.