采用残余应力和力学性能测定、化学成分分析、断口扫描及金相检验等方法对铁路货车用L-B型组合式制动梁撑杆翼板产生裂纹的原因进行了分析。结果表明,由于焊前未预热且焊接工艺不规范，导致在焊缝处存在较大残余拉应力和不良显微组织；焊后又未采取必要措施消除上述缺陷；加上材质本身存在力学性能和化学成分不符合有关标准的要求，使该制动梁在运行中产生裂纹，最终导致失效。提出了改进措施。

The integrated analysis of crack failure for L-B Composite Brake Beam Bar Flange Slab was made by means of SEM, microscope and chemical analysis. The results showed that the essential reason due to early crack on brake beam safety chains bracket is unsuitable welding technology. In concretely, no preheating to brake beam welding zone before welding or much high welding heat input caused higher residual tensile welding stress and disadvantage microscopic structure; no post heating after welding to removing residual welding stress and improve disadvantage microscopic structure; no sanding after welding to removing macro/micro welding defect of the weld toe zone. All the above factors and unqualified mechanical properties and chemical constitution caused the cracking of brake beam.