Wuhan University of Technology

Graduation Project (Dissertation)

Finite Element Analysis and Calculation of

Shot Peening for Automobile Spring Steel

School: School of International Education

Major amp; Class: Automotive Engineering 1401

Student name: Zhang Yudong

Tutor Name: Wang Zhou

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Abstract

In this dissertation, the 50SiMnVB spring steel is taken as the research object. Two different mechanisms of shot peening are studied, namely stress strengthening mechanism and tissue strengthening mechanism. The process of shot peening was analyzed, and the experimental measurement method of shot peening intensity was introduced. By comparing various mechanical surface strengthening processes, the advantages of the shot peening cold treatment process were analyzed. Shot peening is widely used in aviation, vehicles, pressure vessels, steam turbines and other industries due to its advantages such as high adaptability, high versatility, high production efficiency, reasonable equipment costs, and low energy requirements. In the automotive industry, some relatively low-cost components can be quickly updated by changing parts. It is difficult to achieve relatively expensive and dangerous parts. It is better to reduce the weight and reduce the surface hardening process by shot peening. Replacement costs in order to achieve the purpose of improving economic efficiency.

The fatigue failure of the material was analyzed. It was found that the important factor affecting the fatigue life of the material was the surface integrity of the material. By comparing the two fracture criteria, the important role of the stress intensity factor of the crack tip in the fracture criterion was studied. This dissertation establishes the constitutive mechanics model of the material. In the elastic stage, the stress-strain relationship is established according to the generalized Hooke's law. In the plastic stage, the incremental theoretical formula of the stress-strain relationship in the plastic stage is established by the Mises yield criterion. According to Hertz contact theory, the theoretical calculation formula of residual stress at 100% coverage is established.

Using ABAQUS finite element analysis software, a single projectile impact model and multiple projectile impact models with different coverage rates were established. By setting up different shot peening parameters, such as shot peening speed, projectile diameter, boundary conditions and coverage rates, the influence of different shot peening parameters on the residual stress field of the target was studied. Through the weighted average of the parameters, the optimum shot peening parameters under certain conditions are obtained. The results show that shot peening can significantly improve the failure strength of 50SiMnVB vehicle spring steel, plastic deformation of the surface parts, and the formation of a certain thickness of the strengthening layer, to form a higher residual stress in the reinforcement layer. As the shot peening rate increases, the maximum residual stress value also increases. The maximum residual stress depth and the residual stress layer depth also increase with the increase of shot peening speed. When the speed increases exponentially, the maximum residual stress value and the depth of the residual stress layer do not significantly increase exponentially. With the increase of the diameter of the projectile, the maximum residual stress value and the depth of the residual stress layer are also increasing. However, the impact of the diameter of the projectile on the maximum residual compressive stress value is not obvious, and as the diameter of the projectile increases, the depth of the residual stress layer changes gradually. The change of boundary conditions has less influence on the surface residual stress and the maximum residual stress value, and has little effect on the depth of the maximum residual stress and the depth of the residual stress layer, and there is an optimal boundary condition. From the residual stress curve, it can be concluded that there is almost no significant change in the surface residual stress as the shot peening coverage increases. The value of the maximum residual compressive stress increases significantly with increasing shot-peening coverage. When, moreover, the depth of the residual stress layer increases as the shot-peening coverage increases. Different shot peening parameters will produce different shot peening effects. Considering shot peening costs, different shot peening parameters will be generated.

The results of the finite element simulation of the 50SiMnVB spring steel have certain guiding significance for the setting of parameters in the actual shot peening process, and the simulation results also prove that the shot peening can indeed enhance the strength and fatigue life of the metal structural parts.

Key Words: Shot peening; Finite element method; 50SiMnVB; Residual stress

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