M24高强度螺栓低周疲劳试验与理论研究

Low cycle fatigue test and theoretical research on M24 high strength bolt

为探究M24高强度螺栓低周疲劳破坏机理,对18个20MnTiB材质的10.9级M24高强度螺栓进行了低周疲劳试验研究,并针对典型螺栓试件进行宏观和微观断口分析。另外,基于拟合Coffin-Manson公式和幂指函数公式,探讨了疲劳试验加载频率与螺栓低周疲劳寿命之间的关系,并采用ABAQUS和Fe-Safe软件建立有限元模型,进一步探讨了螺栓低周疲劳断裂机理及其影响因素。结果表明:10.9级M24高强度螺栓低周疲劳破坏模式主要分为脆性断裂和非脆性破坏,且疲劳断裂方式与加载频率无明显相关性;疲劳断口扩展区面积占比较少,瞬断区面积较大且更粗糙;疲劳源形核期短,裂纹形核容易,且断口边缘分布多个疲劳源,造成裂纹扩展过程中产生大量二次裂纹,降低了疲劳裂纹扩展寿命;螺栓内部含碳杂质会促进裂纹的萌生与扩展,降低了螺栓的裂纹萌生寿命;当加载频率为0.2 Hz时,螺栓低周疲劳寿命关系更契合幂指函数公式;当加载频率为0.5 Hz时,Coffin-Manson公式拟合程度更好;数值模拟所得螺栓应力集中位置与低周疲劳试验中试件断裂位置基本吻合;Fe-Safe软件模拟高强度螺栓低周疲劳寿命具有一定可行性。

In order to explore the low-cycle fatigue failure mechanism of M24 high-strength bolts,low-cycle fatigue tests of 18 specimens 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 fracture 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 frequency 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.