离合器踏板助力扭簧断裂分析

离合器踏板助力扭簧在行驶2万公里左右时发生多起断裂事故，且断裂位置和形式基本相同，为找出断裂原因，对断裂扭簧进行断口分析、化学成分分析和显微组织分析，并对制造扭簧同批次的钢丝进行力学性能分析和表面缺陷检查，对扭簧的受力进行有限元模拟分析计算。结果表明:扭簧的断裂属单向弯曲大应力疲劳断裂，且裂纹起源于扭簧外表面缺陷处。断裂扭簧在成分、显微组织和表面缺陷等方面均满足标准要求；同批次琴钢丝力学性能满足标准要求。综合分析表明，断裂的主要原因是设计上存在不足，次要原因是扭簧表面存在缺陷。在综合考虑总成匹配和扭力值等因素后，优化了弹簧设计，经台架试验验证和市场检验，取得了满意的结果。

Fracture Analysis of Power Torsional Springs of Clutch Pedal

Power torsional springs of clutch pedal fractured at the same location after service for about 20 000 kilometers.The failure cause of the springs was analyzed by chemical composition analysis, microstructure inspection, and fracture surface analysis.In addition, mechanical properties testing and surface defects inspection were carried out with the same batch of steel wires.The results show that the fracture mode of the torsional springs is fatigue fracture caused by large unidirectional bending stress.The cracks initiated from the surface defects of the torsional springs.The chemical composition, microstructure, and surface defect status can all meet the requirements of the standard.The mechanical properties of the same batch of torsional spring steel wires can meet the requirements of the standard, too.Comprehensive analysis shows that the design insufficiency is the primary cause for the fracture, and the secondary cause is the surface defects of the torsional springs.The design of the springs has been optimized based on assembly matching and torque values, and subsequent tests have shown that the design improvement is effective.