Numerical Simulation Of Torsional Fretting Stress

The torsional fretting is caused by the combined action of the normal force and the small torque on the contact body,and is widely present at the joint portion of the ball valve,the human joint,and the torsional structural member.Torsional fretting wear can cause the ultimate failure of the mechanism and is an undetectable but extremely damaging form of damage.The research on fretting tribology mainly focuses on the tangential fretting,while the research on the whirring fretting mostly adopts the experimental method.The mechanism of the tactile fretting needs further exploration.In this paper,the mechanical properties of the torsional fretting operation are analyzed,and the following results are obtained:?1?The spherical contact model is established,and the relationship between the torque amplitude M₀ and the torsion angle amplitude?₀ and the radius c of the adhesion zone is studied.The variation of the surface tangential stress distribution during torque loading and unloading is obtained,and the hysteresis curve between the torque M and the torsion angle?is obtained.?2?The stress distribution during torque loading is analyzed.Under the action of normal force P alone,the maximum value of von Mises stress appears directly below the contact center.Under the action of pure torque M,the variation of tangential stress component and the characteristics of the most value point are analyzed when the radius of different adhesion zone c is analyzed.Under the combined action of force,the characteristics of stress distribution are specific.There are two extreme points of stress:one is located directly below the contact center,and the other is at the contact surface.?3?In the process of torque unloading,the expression of surface tangential stress is very complicated,and the subsurface tangential stress during unloading can hardly be derived by conventional analytical methods.For this reason,the semi-analytical method is introduced.Firstly,the subsurface stress distribution during loading is solved by the method,and the subsurface stress distribution during loading is compared with the analytical method.Then the reliability of the method is verified.Finally,the semi-analytical method is used to determine the subsurface stress distribution during unloading.?4?The influence of different parameters on the stress distribution during unloading is analyzed.The torque M and the friction coefficient f have the same effect.As the parameter increases,the overall stress increases and the maximum stress increases.The maximum stress point moves from the subsurface to the contact surface.The effect of the radius c of the adhesion zone is the same,but the range of influence is limited,and the stress value changes relatively only in the shallow depth range of the subsurface layer.?5?In the loading and unloading cycle,the position of the maximum stress point on the M-?hysteresis curve is analyzed.It is shown that the larger the friction coefficient f is,the smaller the radius c of the adhesion region is,and the higher the stress point appears on the surface of the contact body or the lower the subsurface ratio.At the same time,it can be seen that at both ends of the curve,that is,when the torque M is large,the maximum stress point is more likely to appear on the surface.At the center of the curve,that is,when the torque M is small,the maximum stress point is more likely to occur on the subsurface.The research results have a reference for the further study of torsional fretting stress.