Analyses of residual stresses on stamped valves by X-ray diffraction and finite elements method

The evolution of the engineering materials, manufacturing processes, as well as of many mechanical parts have required more and more the development of new techniques and methods to their analyses. The metalworking of the metallic materials by plastic deformation generates internal stresses called residual stresses, which can result changes in the materials’ expected mechanical behavior. This paper presents the analyses of these residual stresses in stamped valves by X-ray diffraction and also by the finite element method. Therefore, in this context, it was developed an alternative method to the usual sen2 ψ to determine the residual stresses by X-ray diffraction on small areas, the same method utilized to the residual stresses determination in thin film layers. The results obtained by X-ray diffraction were compared to experimental results as well as to the results from the numeral simulation with the finite elements method (FEM). Fatigue tests were carried out in a endurance bench applying alternate reverse bending on dynamical valves under the following manufacturing conditions: (a) just blanked; (b) blanked and plastically deformed on specific regions of the higher stresses and (c) blanked, plastically deformed and plus an additional abrasive process applied in order to minimize or eliminate regions of the potential crack initiation, previously identified in the numerical simulation. The results obtained in the fatigue tests have proven the validity of the methods used to analyze the residual stresses.