螺杆钻具传动轴接头表面裂纹断裂性能研究

以螺杆钻具的作业载荷为依据,对传动轴上端接头螺纹进行断裂性能研究。首先,通过强度分析,确定接头螺纹易发生断裂的危险位置;然后,考虑材料的弹塑性以及螺纹升角,建立螺纹根部含横向半椭圆表面裂纹的外螺纹接头和相啮合水帽的有限元模型,定量评价弹塑性和螺纹升角对接头断裂性能的影响。结果表明,材料塑性变形和螺纹升角对裂纹前缘J积分的影响较大,忽略这两个因素得到的结果偏于不安全。最后,利用所建立的弹塑性有限元模型,对于上扣预紧力单独作用以及上扣预紧力和工作扭矩共同作用的两种载荷条件,得到螺纹根部裂纹前缘的临界形状比及其对应的量纲为一的J积分随裂纹扩展的变化,为进一步研究螺杆钻具传动轴接头螺纹的疲劳寿命提供依据。

Fracture behavior of surface crack in tool joint of transmission shaft of positive displacement motor

Fracture behaviors of the upper tool joint of the transmission shaft are studied under working load of positive displacement motor.Firstly,based on the strength analysis,the position,where fracture is more easily to occur,is determined on the joint thread.Secondly,considering elastic-plastic constitutive relation of the material and helix angle of thread,a finite element model that includes both a tool joint with a semi-elliptical surface crack and the meshing water cap is established.Influences of plastic deformation and helix angle on fracture properties of tool joint are evaluated quantitatively.It is found that both the plastic deformation and the helix angle have great influence on the J-integral of the crack,and the operating life predicted with the model ignoring these two factors is more dangerous.Finally,under the two loading conditions,i.e.loaded by tension only,and loaded by both tension and operating torque,the critical aspect ratios of the crack and the corresponding dimensionless J-integral are given along with crack propagation.It provides a reference for life prediction about the tool joint thread of the transmission shaft of the PDM.