Failure analysis of bolts on fatigue test bench for excavator stick

Abstract

In this study, a new bench device with full-scale fatigue test for excavator stick was designed. The test bench has the function of dynamic load self-balancing, because a part of the load applied to the specimen of stick is directly transferred to the pillars of the test machine through the high-strength bolts connection. Accordingly, the ground under the test machine was not affected by the test load. However, some bolts located on the fatigue test bench failed and fractured during fatigue testing for excavator stick. To determine the failure reasons of bolts, mechanical and scanning electron microscope (SEM) analyses were conducted. The tensile stress of bolt group under ultimate load was evaluated via finite element model (FEM) of test bench according to test load spectrum. Moreover, under the test load spectrum, the stress range of bolt group was obtained and the fatigue life prediction of bolts was conducted by referring to Eurocode 3. It should be noted that the results of numerical simulation of fatigue lives for failure bolts were consistent with the actual lives of failure bolts during test. A fractured surface on one of the failed bolts was examined by SEM observation to determine the failure initiation and failure mode.