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

Abstract

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 sen 2 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.

Influence of Heat Treatment on Residual Stress in Cold-Forged Parts

“…Consequently, the cold forging condition (A3) introduced greater compressive residual stress at the measurement points (P1, P2, and P3). This is consistent with previous results in the literature, such as the work of Martins et al [4] previously mentioned. Compressive stress is beneficial for parts that are subject to cyclical loads because it helps to prevent the initiation and propagation of cracks.…”

“…Forming processes are also responsible for introducing residual stress in parts. Martins et al [4] deformed one region of a stamped valve to introduce compressive residual stress, thereby improving the valve's fatigue strength. Machining is another source of residual stress.…”

Influence of the edge rounding process on the behaviour of blanked parts: numerical predictions with experimental correlation

“…In the following, the von Mises equivalent stress is used to define and compare the residual stress state, which is by definition is a complex three-dimensional stress state with interaction between the components of the stress tensor. This is common approach used by other authors [23]. Figure 20 shows the comparison between the numerically simulated blanked profile and the experimentally observed profile.…”

Design Criteria for High Power Engines Crankshafts

“…This is a quite useful assumption that allows to have a quick response but in many cases is not enough to assure the resistance of the component. On the other hand the finite element method enables the designer to develop quite accurate numerical models in which all kind of loads, boundary conditions, pre-stress, residual stresses and surface treatment effects of any kind can be simulated [27][28][29]. Nevertheless such analyses are often time consuming and expensive and requite a good level of knowledge of the numerical approach and analysis of the results.…”