The metal sheets play an important role in the mechanical design, particularly in the aerospace structures. The rivet connections are frequently used to connect these sheets. The riveting quality greatly influences the rupture of the rivet and the sheet. The various parameters affect the quality of this operation. In this paper, the optimization of the parameters contributing to the riveting quality in order to minimize the value of the maximum tangential stress in the sheets is addressed. To this end, the tolerance of the hole diameter in the top and the bottom sheets, the friction coefficient, and the tolerance of the rivet diameter and the rivet length were considered as the parameters influencing the riveting quality. A total of 64 models were obtained by the permutations of the parameters two at a time. The outputs were determined using the finite element method. The objective function for the optimization is the maximum tangential stress for which there is no analytical relation. Thus, three methods including the multivariable linear regression (MLR), the artificial neural network model of the radial basis function (RBF) type, and the hybrid model of the artificial neural network and the genetic algorithm (ANN-GA) were employed to model this function. Further, the performance of the three models was compared and the most suitable one was selected to model the objective function. The regression model was used to model the values of the height and the diameter after riveting. The imperialist competitive algorithm is utilized to solve this optimization problem. The obtained value for the maximum tangential stress using the imperialist competitive algorithm is 16368 pounds per square inches. After modification, this value increased to 23440 pounds per square inches using the finite element method. . The 0.07689 inches and 0.18524 inches were obtained for the height and diameter of the rivet after riveting, respectively. پرونده مقاله

Among assembling methods, welding is most widely used in various industries. During the welding operation, material is heated to a temperature above the melting point and melted material forms a weld pool. This leads to the formation of tensile residual stresses in the weld toe. In this paper, effect of burr grinding technique on fatigue strength of butt-welded joint has been evaluated. Burr grinding is one of the weld geometry modification methods that with removing small crack-like defects at the weld toe and increasing weld toe radius leads to reduction of stress concentration factor (SCF) and improvement of fatigue strength of weld. Also, the finite element simulation was performed by using ABAQUS software and stress concentration factor was chosen as a criterion. This factor was calculated using analytical and numerical methods for samples before and after grinding. Burr grinding procedure on welded samples was done using an electric grinder and different conical burrs. Burrs with different radii have been selected in order to provide a better comparison. Fatigue life of samples before and after grinding was determined by fatigue tests under constant amplitude loading. The results show 43.72 percent improvement in stress concentration factor and 50.61 percent improvement in fatigue life of samples. In experimental study, the best result belongs to grinding with a 3 mm tapered burr leading to an improvement of 50.61% in fatigue life while grinding with 1 mm tapered gives the worst result of 8.88% improvement in fatigue life. پرونده مقاله

The researchers have shown that there are cracks in the toe weld and they have an important role in the welding failure. The elimination of these shortcomings and the improvement of the fatigue life have always been a concern for the industrial designers. One method of improving the fatigue life of the welded joint at its geometry branch is to remelt the toe region of the steel weldments using the Tungsten Inert Gas (TIG) method or TIG-dressing. This method affects the material structure, hardness, stress coefficient and welding shape. In this study, the effectiveness of this method on fatigue and stress concentration at the weld toe was investigated. The experimental results showed that the toe weld form was changed by TIG – dressing and thus increased the radius and decreased the toe weld’s angle, so that the stress was reduced by TIG – dressing. Also, the fatigue tests showed that the fatigue life increased by an average of approximately 30 percent. Finally, the stress concentration factors were obtained using ABAQUS finite element analysis. The amount of stress concentration factors in weldments before and after TIG – dressing were respectively achieved to be 2.4 and 1.3. پرونده مقاله