某汽车发动机曲轴失效分析

Failure Analysis of an Automobile Engine Crankshaft

摘要:

发动机曲轴是汽车最重要的部件之一，其主要功能是将活塞的往复直线运动转换为旋转运动并输出扭矩，同时将活塞产生的功转变为有用扭矩。曲轴在工作过程中会承受气体惯性力、往复惯性力及扭转惯性力等周期性载荷作用，极易导致失效，且失效往往是突发性的缺乏先兆，一旦发生将会造成重大损失。随着用户对产品质量和可靠性要求的提高，研究曲轴早期失效的原因变得尤为重要。针对某汽车发动机曲轴开裂的失效事故开展了调查和研究，通过对事故发生前期的使用情况及维护保养情况的调查，以及对曲轴的宏观形貌、开裂面的宏观及微观形貌、化学成分、金相组织、连杆颈表面淬硬层深度和基体力学性能等方面的研究，深入分析了曲轴开裂的原因，讨论了失效过程。结果表明，长期承受多种周期性载荷作用，产生应力集中是导致曲轴在最薄弱处发生疲劳断裂的主要原因。这一研究为改进曲轴设计、制造工艺和使用维护提供了科学依据，以提高其可靠性和延长使用寿命。

Abstract:

The engine crankshaft is one of the most critical components of an automobile， primarily responsible for converting the reciprocating linear motion of the piston into rotational motion and transmitting torque. Additionally， it transforms the work done by the piston into useful torque. During operation， the crankshaft is subjected to various periodic loads， including gas inertia force， reciprocating inertia force， and torsional inertia force， making it prone to failure under these conditions. Crankshaft failure is often abrupt and lacks significant early warning signs. Once a failure occurs， it can result in substantial losses. In recent years， there has been increasing emphasis on stability and reliability of product quality. Therefore， it is very important to carry out investigation and experimental analysis of early failure incidents of crankshaft and find out the causes of failure. This paper investigates and studies a failure incident involving the cracking of an automobile engine crankshaft. First， the initial conditions of the accident were investigated， focusing on usage and maintenance records. Next， experimental research and analysis were carried on the macroscopic morphology of the crankshaft， the macroscopic and microscopic morphology of cracked surface， chemical composition， metallographic structure， the depth of hardened layer on the surface of connecting rod neck and the mechanical properties of the matrix. Finally， the causes of the crankshaft cracking were analyzed， and the failure process was discussed. The diagnosis concluded that prolonged exposure to various periodic loads led to the stress concentration and subsequent fatigue fracture occurred at crankshaft's weakest point.