采用直读光谱仪、显微硬度机、光学显微镜和扫描电子显微镜等分析手段，对失效的汽车发动机活塞连杆总成断裂原因进行了分析。断裂首先发生于连接大盖，裂纹源位于凹槽端面底部应力集中严重的过渡R处，该处还存在加工刀痕，更加剧了应力集中程度。连杆总成在承受了多次反复冲击载荷后，在该处首先产生了裂纹源，发生了疲劳断裂，之后连杆总成正常运动状态受到破坏，连接螺栓接着发生了一次性韧性断裂。
Aemission spectrometer, microhardometer, optical microscope and scanning electron microscope were used to analyze the reason of crack on connecting rod unit assembly for piston of car engine. The crack occurred to the connecting cap first, and the cracks source was situated at the transition region of R at the bottom of the recess where exist sharp stress concentration, The finished surface with tool marks had increased stress concentration further. Under acting of alternative stress on the connecting rod unit assembly, the cracking source taken place in the transition region of R at the bottom of the recess hole, and fatigue cracking occurred first, so the normal working state of the connecting rod unit assembly had been changed, That caused the tough fracture in joint bolt.
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