用直裂缝平台巴西圆盘确定混凝土的动态断裂韧度

采用一种直裂缝平台巴西圆盘试件，在分离式霍普金森压杆系统上研究了混凝土动态起裂韧度的测试方法。该方法基于一维应力波理论，利用压杆上的应变信号计算试件所受的动态冲击载荷P(t)，结合动态有限元法求得试件相应的动态应力强度因子KI(t)，再由试件上应变片测得的起裂时间tf对应的临界动态应力强度因子KI (tf)，即为混凝土的动态起裂韧度KId。试验表明，混凝土的动态起裂韧度高于在材料试验机上测得的静态断裂韧度，因为在动态加载情况下，圆盘试件除在预制裂缝方向产生与静态加载一样的裂缝扩展外，还产生大致平行于预制裂缝方向的多重裂缝扩展破坏现象。试件破坏模式、临界破坏时间等是影响混凝土材料动态起裂韧度测试结果的重要因素。

Determination of dynamic fracture toughness of concrete using cracked straight-through flattened Brazilian disc

The cracked straight-through flattened Brazilian disc (CSTFBD) specimens were used to study the test methods for dynamic initiation toughness of concrete using split Hopkinson pressure bar system. The method is based on the one-dimensional stress wave theory, the impact load P(t) applied on the specimen is got from the strain signals measured on the bars, and the fracture time tf is got from the strain gauges stuck on the crack tip of the specimen. The dynamic stress intensity factor history KI(t) is calculated using the impact loading P(t) as input for the finite element analysis, and the dynamic initiation toughness KId is the critical dynamic stress intensity factor KI(tf). The results shows that the dynamic initiation toughness is higher than the corresponding static fracture toughness tested with a material testing machine. In the dynamic loading, the extending cracks occur not only along the prefabricated crack direction like the static loading, but also along other directions, which are approximately parallel to the prefabricated crack of the specimen. The specimen breakage mode and the critical fracture time are important factors which will affect the test result of dynamic initiation toughness of concrete .