Investigation of failure mechanism of a DCI engine connecting rod

Abstract

In reciprocating engines, connecting rod cap and connecting bolts are critical as they are exposed to varying loads under different operating conditions. This paper focuses on the failure of the connecting rod of a 1.5 dci K9K diesel engine. As a result of the engine operating for approximately 378400 km, the connecting rod was broken, and the reasons for the failure of the connecting rod cap and connecting bolt were investigated. The connecting rod of the K9K engine was designed in accordance with the dimensions by using SolidWorks software, and then exported to ANSYS software for stress and fatigue analysis. Also, the macrostructure of the broken connecting rod cap and bolt was investigated. We that the mechanic who fixed the engine about two years ago tightened the connecting rod bolts without using a torque meter. Therefore, stress and fatigue analyses were performed to determine the effect of different tightening torques (ranging from 22.5 to 52.5 Nm) at 2000 rpm. According to the numerical analysis results, with increasing tightening torque, the maximum equivalent stress and alternating stress values increased significantly, while the fatigue safety factor and the cyclic life of the connecting rod decreased. First, a fatigue fracture occurred in the right hand bolt. Immediately after, the lower cup deformed and crashed to the cylinder liner. Therefore, a brittle fracture occurred on the left shoulder of the connecting rod shank. The chevron markings were clearly visible in the macrostructure as evidence of brittle fracture.