Microstructures and mechanical properties of the fractured bridge detection vehicle are investigated by scanning electron microscopy, and tensile tests in this paper. The finite element analysis shows that the maximum stress which is close to the material yield limit is near the fracture position. When the frame platform of the bridge detection vehicle bears a large combined load, it will cause the crack to propagate from inside to outside gradually, and finally, lead to the fracture of the weld of the frame platform. Microstructures show that there are a lot of gas holes in the weld and a long unwelded zone with the exception of ferrite and pearlite. Moreover, the layout of the accident vehicle frame platform is unreasonable, and the design and layout of the weld seam make the flange and frame platform weld unable to provide enough bearing capacity, thus leaving potential security risks for the accident.

通过扫描电子显微镜和拉伸试验研究了桥梁断裂检测车的组织和力学性能。有限元分析表明，接近材料屈服极限的最大应力接近断裂位置。当桥梁检测车的框架平台承受较大的组合载荷时，会导致裂纹逐渐从内向外传播，最终导致框架平台焊缝断裂。显微组织表明，除了铁素体和珠光体外，焊缝中有很多气孔，并且有一个长的未焊接区域。而且，事故车架平台的布局不合理，