M. Sedighi

An approach in prediction of failure in resistance spot welded aluminum 6061-T6 under quasi-static tensile test

The aim of this article is to predict the failure load in resistance spot welded aluminum 6061-T6 sheets with 2u2009mm thickness under quasi-static tensile test. Various welding parameters, e.g. welding current, welding time and electrode force are selected to produce welded joints with different quality. The results show that for all the samples in this study only interfacial failure mode was observed in tensile-shear test and no pull-out mode was observed. According to the failure mode, an empirical equation was used for the prediction of failure load based on nugget size and hardness of failure line. Microstructure study has been carried out to investigate microstructural changes in the welded joints. For determination of the minimum hardness, microhardness tests have been carried out to find hardness profiles. The minimum hardness value was observed for a thin layer around the nugget with large and coarse grains. The results show that by using the presented empirical equation, the failure can be predicted with a good agreement only by measuring nugget size.

On Residual Stresses in Resistance Spot-Welded Aluminum Alloy 6061-T6 : Experimental and Numerical Analysis

In this study, an electro-thermal-structural-coupled finite element (FE) model and x-ray diffraction residual stress measurements have been utilized to analyze distribution of residual stresses in an aluminum alloy 6061-T6 resistance spot-welded joint with 2-mm-thickness sheet. Increasing the aluminum sheet thickness to more than 1xa0mm leads to creating difficulty in spot-welding process and increases the complexity of the FE model. The electrical and thermal contact conductances, as mandatory factors are applied in contact areas of electrode-workpiece and workpiece-workpiece to resolve the complexity of the FE model. The physical and mechanical properties of the material are defined as thermal dependent to improve the accuracy of the model. Furthermore, the electrodes are removed after the holding cycle using the birth-and-death elements method. The results have a good agreement with experimental data obtained from x-ray diffraction residual stress measurements. However, the highest internal tensile residual stress occurs in the center of the nugget zone and decreases toward nugget edge; surface residual stress increases toward the edge of the welding zone and afterward, the area decreases slightly.

Design and development of an incremental sheet metal hammering system using mass damper

Incremental forming is a method for rapid-prototyping and low-volume production. Incremental sheet metal hammering is relatively a new technique in which successive blows of punch on the clamped sheet are used to apply desired shape. In this article an incremental sheet metal hammering system has been designed and developed. The developed mechanism is equipped with a cam shaft including some hard metallic balls as dampers into the central driver core. It can reduce the system vibration to some degree. This research describes the theoretical, simulation and practical background of the designed system. In addition, experiments are accomplished to assess the tool performance. Also, by evaluation of experimental results, the effects of some parameters on the surface quality and maximum forming angle have been studied.

Prediction of residual stresses in resistance spot weld

Purpose n n n n nThe purpose of this paper is to predict residual stresses in resistance spot weld of 2 mm thick aluminum 6061-T6 sheets. The joint use of finite element analysis and artificial neural networks can eliminate the high costs of residual stresses measuring tests and significantly shorten the time it takes to arrive at a solution. n n n n nDesign/methodology/approach n n n n nFinite element method and artificial neural network have been used to predict the residual stresses. Different spot welding parameters such as the welding current, the welding time and the electrode force have been used for the simulation purposes in a thermal-electrical-structural coupled finite element model. To validate the numerical results, a series of experiments have been performed, and residual stresses have been measured. The results obtained from the finite element analysis have been used to build up a back-propagation artificial neural network model for residual stresses prediction. n n n n nFindings n n n n nThe results revealed that the neural network model created in this study can accurately predict residual stresses produced in resistance spot weld. Using a combination of these two developed models, the residual stresses can be predicted in terms of spot weld parameters with high speed and accuracy. n n n n nPractical implications n n n n nThe paper includes implication for aircraft and automobile industries to predict residual stresses. Residual stresses can lower the strength and fatigue life of the spot-welded joints and determine the performance quality of the structure. n n n n nOriginality/value n n n n nThis paper presents an approach to reduce the high costs and long times of residual stresses measuring tests.

Mechanical Properties and Microstructure of Mg-SiC p Composite Sheets Fabricated by Sintering and Warm Rolling

In this study, magnesium matrix composite sheets were fabricated by applying powder metallurgy and warm rolling methods. After preparing required mixtures of magnesium powder and SiC particles in different conditions, they were cold-pressed and sintered. Then, the sintered specimens were warm rolled through different numbers of passes. The effects of ball-milling process and the number of rolling passes were investigated on the tensile strength, hardness, microstructure, and fracture surface of magnesium matrix composites. The results were compared to those monolithic magnesium specimens (without reinforcement particle) produced in a way similar to that of the composites. The results show that among different factors (i.e., ball-milling process, the presence of SiC particles, and the number of rolling passes), the number of rolling passes is the most effective parameter on increasing the ultimate tensile strength (UTS),Vickers microhardness, and grain refinement. In this regard, UTS of the samples was increased at least 163% between second and sixth rolling passes. Moreover, for the sintered and six-pass rolled composite samples, microhardness and grain refinement were improved, respectively, about 30 and 70%.