The aim of this work is to take into account the effect of the stress gradient as a beneficial effect in fatigue, since its presence within a material systematically leads to an increase in the endurance limit in terms of local maximum stress. We have therefore proposed that the stress gradient be taken into account in the fatigue criterion using a statistical approach based on the variance method. This method assumes that the fracture plane is the one on which the variance of the equivalent stress is maximum. This method defines three types of equivalent stress on a plane: normal stress, shear stress and combined normal and shear stress. The results obtained using the simple variance method and the stress gradient method were compared for a cyclic biaxial loading condition. We found that in terms of prediction of the fracture plane, there is not much difference between the two formulations (the simple variance method and the one taking into account the stress gradient), but the maximum values of the variance for the variance method taking into account the stress gradient vary greatly compared to the case of the simple variance method.

This article is a comparative study of metallurgical characteristics of the different aluminium alloys gotten through recycling of recovered aluminium in Cameroon. A simple experimental device for the foundry of secondary aluminium blend, of very good quality built around a movable charcoal furnace is presented. It enables better energy efficiency, a better distribution of the heat around the crucible and indirectly assures good quality of the products obtained, while respecting the economic constraints and users' safety. Six refining methods are proposed by the addition of polyvinyl chloride (method A), coke rich in carbon CH_S (method C), ammonium chloride NH₄Cl (method E), manganese dioxide MnO (method T), acrylic nitrite (C₂H₃Cl)_n (method P) and sodium chloride NaCl (method S). A critical analysis of the different recycling techniques is presented as well as a proposed process of melting and refining that enables the obtaining products with high degrees of purity. The results are then compared to the results obtained from the industrial methods of aluminium refining such as fractional crystallization (FC), granular filtration (GF) and dissolution in a metal solvent (DS). The later (DS) gives the rate of 6.540% of accumulated alloy elements and enables the best purification (93.460%), while the NaCl gives the lowest global rate of additive elements (9.478%), with the best purity index (90.522%) amount the proposed methods. Results obtained show that this method of refining improves the metallurgical properties of secondary aluminium alloy blends and guarantees better safety, as well as reducing the risks of environmental pollution.