车辆悬架螺旋弹簧断裂失效行为研究

Study on Failure Behavior of Spiral Spring for Automotive Suspension System

目的判定车辆悬架螺旋弹簧失效的原因,提出改进措施。方法通过分析和测试其化学成分、氢含量、非金属夹杂物、力学性能、金相组织、断口形貌等,研究车辆悬架螺旋弹簧的失效行为。结果试件弯曲变形内侧的剪切应力值最大,容易引起应力集中。材料最后断裂区为韧窝和沿晶的混合断裂,且断后伸长率偏低。喷丸并未完全去除脱碳层及表层的其他原始缺陷,表层形成疲劳缺陷的可能性增高。喷丸造成螺旋弹簧表层存在较深的凹坑,凹坑边缘形成明显凸起棱边,引起应力集中,且材料表层存在折叠缺陷。在循环应力作用下,凹坑处折叠缺陷端部首先成为裂纹萌生点,在循环应力作用下,裂纹持续扩展,最终疲劳断裂。结论减小钢丸粒径,降低喷丸压力,以避免过深的凹坑及尖锐的凸起棱边,并适当增加喷丸过程的表层去除深度;调整热处理工艺,适度降低材料强度、提高韧性,使断后伸长率大于10%。改进轧制工艺,消除材料的折叠缺陷,加强材料缺陷检测。

In order to put forward improvement measures,the causes of the failure of spiral springs for vehicle suspension are researched.The failure behavior of spiral spring is concluded based on the analysis of several tests such as chemical component test,hydrogen content test,non-metallic inclusion test,mechanical property test,fracture morphology analysis and microstructure analysis.The maximum shear stress is in the inner side of the specimen,where the stress concentration is easily caused.The elongation after fracture is low,and the brittle fracture can be seen.The decarburized layer and other original defects on the surface are not completely removed by shot peening,so the possibility of forming fatigue defects on the surface is increased.Due to shot peening,there are deep pits on the surface of the spiral spring,and obvious convex edges are formed on the edge of the pits,resulting in stress concentration.Under the action of stress,the end of the fold defect in the pits becomes the crack initiation area.Under the action of cyclic stress,the crack continues to expand and finally causes fatigue fracture.The shot size and pressure should be reduced,to avoid deep pits and sharp convex edges.In addition,the removal depth of surface layer in shot peening process should be increased appropriately.The heat treatment process should be adjusted to reduce the strength and improve the toughness of the material,so that the elongation after fracture can be more than 10%.The rolling process should be improved to eliminate the folding defects,and the detection of material defects also should be strengthened.