中文摘要：

为探寻低碳钢三点弯曲试样断裂过程与承载能力，分别对不同尺寸的带裂缝试件进行加载试验，并对其中的典型试件进行应变片电测跟踪测试，得到了一系列关系曲线，其中有载荷与加载点位移关系曲线，中性层位置随载荷变化曲线，塑性段卸载再加载关系曲线等；且计算了各试件失稳时的应力强度因子．同时测量了该试样的塑性变形，并结合黏聚裂纹应力强度因子计算式与断裂准则，得到计算此材料结构承载力的理论值，并与试验值进行对比，两者比较符合．

英文摘要：

To investigate the fracture process of the three-point bending low carbon steel ana the calculation method of the peak bearing capacity, the experiments with the incision speci- mens of different sizes were carried out, in which the typical specimens were tested with e- lectrical strain gauges. As a result, a series of experimental curves were obtained and ana- lyzed, such as the curves of displacement of loading vs load; the beam neutral layer position vs load, the unloading and reloading curves during the plastic stage, etc. , and the stress in- tensity factors of the incision specimens with different sizes were calculated. Meanwhile, the plastic deformation was measured. The structure bearing capacities were obtained through the calculation formula of the stress intensity factor and the fracture criterion, which are in agreement compared with the test results.