相对切口深度对混凝土断裂性能影响试验研究

以双K断裂模型为理论基础,采用混凝土标准三点弯曲梁试件,通过试验测得相对切口深度a0/h为0~0.6的5组试件的起裂荷载P_(ini)、断裂荷载P_(max)及临界裂缝口张开位移CMOD,计算得到起裂韧度K_(Ic)~(ini)、K_(Ic)~(un)断裂韧度,并使用立体显微镜对破坏后的混凝土进行切口尖端裂纹以及断裂面观察,探究其裂缝开展情况,以分析相对切口深度对混凝土断裂性能的影响。结果表明:相对切口深度越大,则试件起裂越早,而起裂荷载与断裂荷载的比值随初始缝高a_0的增大无明显变化,初始缝高对起裂荷载和断裂荷载的影响呈线性相关;起裂韧度和断裂韧度随着相对切口深度的增大无明显减小趋势,两者的比值随相对切口深度也无明显变化,即双K断裂参数取决于材料本身固有特性,与切口深度无关;混凝土断裂过程复杂,存在明显的亚临界扩展阶段,该阶段裂纹绕开骨料发展,整个断裂过程中裂缝扩展路径呈现出曲折型。

The experimental study on the influence of relative notch depth on concrete fracture properties

Based on the theory of Double-K fracture model, and by using the standard three-point bending concrete specimens, the initial crack load P_ini, fracture load P_max and critical mouth open displacement (CMOD) of five specimens with relative notch depth a₀/h of 0-0.6 were measured in the experiment, and the initial fracture toughness K_Icⁱⁿⁱ and unstable fracture toughness K_Ic^un were also calculated. The crack tip and the fracture surface were observed by using a stereomicroscope to investigate the crack development, and the influence of the relative notch depth on the fracture performance of the concrete was analyzed. The results indicate that the larger the relative notch depth is, the earlier the specimen starts cracking, but the ratio of the initial crack load to the fracture load does not change with the increase of the initial seam height a₀: the initial seam height is linearly related to the effect of initial crack load and fracture load. The initial fracture toughness and unstable fracture toughness did not decrease with the increase of the relative notch depth. The ratio of the two had no obvious change with the change of the relative notch depth, that is, the double-K fracture parameter depends on the inherent characteristics of the material itself and irrelevant to the relative notch depth. The fracture process of concrete is complicated, and there is a significant subcritical expansion stage. The subcritical crack growth appeared a kink path, by passing the aggregate in the process of development.