In order to study the forced state of drive shaft on the positive displacement motor (PDM)in the three-dimensional borehole trajectory space,a mechanical model of straigh thread with screw lift angle was proposed according to the finite ele-ment control equations of thread connection. The finite element calculation was carried out,and the strength of connecting thread under the corresponding conditions was studied. The results showed that under the effect of compression,torsion,and combined bending and torsion load respectively,the overall stress of pin thread end was 3-4 times larger than that of box thread. The compression load was also an important reason of connection thread gluing. The drive shaft joint received the greatest influence by the combined bending and torsion,followed by the torque load,and the least influence by the compres-sion load. The yield failure of thread joint might be caused by the long term work under the combined bending and torsion load. The results will help to make qualitative and quantitative judgment about the mechanical strength of drive shaft,and provides a new understanding for further study on the force of drive shaft connection thread.%为了研究螺杆钻具传动轴在三维井眼轨迹空间中的受力状态,根据螺纹连接的有限元控制方程,建立1种带螺旋升角的直扣螺纹力学模型,采用有限元方法对其进行计算,研究相应工况下连接螺纹的强度,结果表明:分别在压缩、扭转、弯扭组合载荷作用下,公扣螺纹端整体受到的应力比母扣螺纹要大3~4倍;压缩载荷也是连接螺纹粘扣的重要原因;传动轴接头受到弯扭组合作用的影响最大,其次为扭矩载荷,影响最小的是压缩载荷;长期在弯扭载荷作用下工作,会导致螺纹接头发生屈服破坏.以上结论有助于对传动轴的力学强度进行定性和定量判断,为进一步研究传动轴连接螺纹的受力提供了1种新的认识.
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