For many years, researchers have been looking for a reliable law that will take into account the type of loading, the mechanical characteristics of the material, the geometric configuration in the determination of the service life of mechanical parts. The service life of structures at risk (automotive, aeronautics, among others.) in service, subjected to variable solicitations in time, are random for a same type of loading. This article proposes to highlight the influence of this variation in service life on the reliability of structures by a probabilistic approach. The characteristics of the proposed law are satisfactory compared to the classical laws because it takes into account the parameters of the classical laws (Weibull law) and the dispersions of the lifetimes of a same material.
The welding process led to the heating of very heterogeneous metals, some volumes of matter know that the high temperature causes their fusion. The cooling after fusion is also heterogeneous from considering the speed in which the temperatures change. The solidification of the molten zone and the complete return of that heated to the ambient temperature cause local modifications in the microstructure of metals due to constraints and residual deformations. They are generated at the same time by heterogeneity of the variations in temperature, of the crystalline transformations related to the heat treatment of welding and the efforts related to the side pressure of the electrodes through which circulates the current necessary to welding. Stress levels alone do not justify the fatigue behaviour of material when it does not present homogeneous properties of fatigue strength in the studied volume. Nevertheless, the distribution and stress levels encountered are a valuable contribution to the understanding of local fatigue damage, the sensitivity of stress levels and their spatial distribution in the welded point and their immediate vicinity will be studied in relation to several geometric parameters. The digital model implemented thus aims to identify the critical zones of the welded point and to quantify the influence of certain geometrical risks. Thus, the established model and the results of calculations carried out correlate in a very satisfactory way the experimental results obtained on the test piece welded by point.
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