Low cycle fatigue test and theoretical research on M24 high strength bolt
In order to explore the low-cycle fatigue failure mechanism of M24 high-strength bolts,low-cycle fatigue tests of 18 speci-mens made of 20MnTiB material and rated at 10.9 were carried out.And macroscopic and microscopic fractographic analyses were conducted on typical bolt specimens.Additionally,the relationship between fatigue test loading frequency and low-cycle fatigue life of the bolts was discussed by using the Coffin-Manson equation and power law function.Finite element models were built by using ABAQUS and Fe-Safe software to further investigate the low-cycle fatigue fracture mechanism and its influencing factors.The results reveal that the low-cycle fatigue failure modes of the 10.9-grade M24 high-strength bolts primarily include both brittle frac-ture and non-brittle failure,and no significant correlation between fatigue fracture mode and loading frequency is observed.The fatigue crack propagation area is relatively small,while the instantaneous fracture area is larger and rougher.The crack nucleation period during fatigue initiation is short,and crack nucleation is relatively easy.Multiple fatigue sources were distributed along the fracture edge,leading to the generation of numerous secondary cracks during crack propagation,which reduces the fatigue crack propagation life.The presence of carbon impurities within the bolt promots crack initiation and propagation,thus decreasing the crack initiation life of the bolt.The power law function shows a better fit with the relationship between fatigue life and loading fre-quency when the loading frequency was 0.2 Hz,while the Coffin-Manson equation exhibits a better fit at a loading frequency of 0.5 Hz.The stress concentration positions obtained from numerical simulations are in close agreement with the fracture locations of the specimens in the low-cycle fatigue tests.The Fe-Safe software exhibits some feasibility for the simulation of the low-cycle fatigue life of high-strength bolts.
high-strength boltlow-cycle fatiguefatigue testingfracture analysisfatigue life
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