Study on Effect of Tightening Torque on Fatigue Properties of SWRM10K Steel Bolts
Axial loading fatigue tests were carried out on SWRM10K steel bolts with tightening torque of 0,12.5,22.0,29.5 and 35.0 Nm respectively,and the fatigue S-N data of the bolts were obtained.By comparing the S-N characteristics under different tightening torque,the fatigue performance of bolts was analyzed.The fracture morphology of the bolt sample was observed by SEM,and the element distribution in the crack initiation zone was analyzed by EDS,revealing the rule of fatigue fracture of the bolt.The research results show that increasing the tightening torque can effectively improve the fatigue limit of the bolt,but as the increase goes to a certain extent,the lifting effect obviously deminishes,and the tightening torque value close to 29.5 Nm is more reasonable.Under this tightening torque,the fatigue limit of the bolt is 141 MPa,which is 62.1%higher than that without tightening torque.Fatigue fracture surfaces of the bolts are divided into three regions:crack initiation region,crack propagation region and instant fracture region.Under high stress amplitude,crack initiation occurs on the specimen surface caused by crystal slip,while under low stress amplitude,crack initiation occurs on the surface caused by crystal slip or inclusions.
万方数据
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