The cross cardan shaft of screw drill is the key structure to transmit torque and speed.The relative sliding between the locking shaft and the ball socket in the motion pair always leads to accelerated wear of the body structure,significantly reducing the service life of the cardan shaft.In order to study the influence of the radius of the circular arc surface of the locking shaft and ball socket on the sliding wear,a three-dimensional wear simulation physical model with different radius of the circular arc surface was established.The contact boundary conditions of the simulation model were set based on Hertz contact theory and Archard wear theory.The changes of wear volume,maximum deformation,maximum sliding distance and maximum penetration depth under different radius were studied.The structure morphology and the distribution of the wear area of the non-sealed cross cardan shaft after sliding wear between the locking shaft and the ball socket were studied by field tests.The results show that,within a certain range,with the increase of the radius of the circular arc surface,the wear volume decreases first and then increases,the maximum slip distance and the maximum penetration depth decrease gradually,and the maximum deformation is less affected by the radius of the circular arc surface.The recommended optimal radius is from 28 mm to 30 mm.The simulation analysis and experimental results indicate that the sliding of the locking shaft and ball seat will cause significant wear on the convex surface of the locking shaft,and there will be “sharp corners” at the edges along the circumferential direction,the thickness of the concave surface of the ball seat arc will decrease,forming a circular groove and exhibiting “curling deformation”.The research can provide reference for the structural optimization design and the improvement of wear resistance of the moving pair of the universal joint shaft.