مجله مهندسی ساخت و تولید ایران
سال نهم شماره 11 (بهمن 1401)

Determining the internal structure of objects such as identification of impurities, estimation of mechanical properties and identification of internal boundaries and cavities is one of the important issues in industries. Objective of the present article is to investigate the effect of the mechanical properties and the effect of the location of the interfacial boundary in solving the inverse problem of identifying the internal boundaries of a Non- homogeneous body, consisting of two homogeneous bodies, along with the estimation of the modulus of elasticity and Poisson's ratio of its components. The solution has been done using the combination of the numerical method of boundary elements method along with the optimization method of the Imperialist Competitive Algorithm (ICA) and the simplex method. The obtained results, show the effectiveness of the ICA optimization and the simplex method in estimating the mechanical properties and identifying the interfacial boundary configurations. But, as the boundary approaches the lower part of the material and the mechanical properties approach, the boundary estimation error increases to 8.65% for the solved examples, which again indicate the strength of this method to estimate the boundary. Also, in the investigation of the effect of unavoidable errors in the measurement of displacements, with the increase in the error percentage, the convergence to the real boundary is reduced, so that for error greater than 5%, the geometry of the internal boundaries converges to unrealistic boundaries and the calculations are no longer valid.

Porous structures are of interest to researchers from different fields due to their multiple functions. In this research, the quality of energy absorption of porous structures designed based on Schwarz P minimal surface is investigated. For this purpose, three cubic samples are designed and tested using pressure test. Two samples of polylactic acid, one of which is completely solid and the second with 50% porosity are printed using the fused deposition modeling method. The third sample is made of UV resin with 50% porosity, using the masked stereolithography apparatus. In the following, all three samples are subjected to a pressure test, and force-displacement and energy-displacement diagrams are extracted. The obtained results show that the behavior of the resin sample is completely brittle and does not have ductility and the ability to absorb energy. In contrast, the PLA sample has undergone deformation up to 70% strain. Also, the comparison of two solid and porous polylactic acid samples shows that the amount of energy absorbed in the porous sample is about one-third, but the absorption quality is soft and smooth.

Haptic Devices (HDs) are used to simulate virtual objects for the user. The dynamics of the HD and the opertator’s hand have a great effect on the stability and performance of the HD. In this research, the dynamic identification of the user's hand and HD has been done using methods of Artificial Bee Colony Optimization (ABCO), Crow Search Algorithm (CSA), and Genetic Algorithm (GA), during experiments in two cases. In the first case, only the dynamics of the HD has been identified, then in the second case, the mentioned methods have been generalized for the simultaneous recognition of the dynamics of the user's hand and the HD. For this purpose, first, in each case, the theoretical stability boundary is obtained as a function of the available dynamic parameters. Then, by performing experiments on the KUKA Light Weight 4 robot in two cases of presence and absence of the operator’s hand, the experimental stability boundary has been obtained. Afterwards, by using ABCO, CSA, and GA in each case the desired dynamic parameters are obtained in such a way that the difference between the theoretical and experimental stability boundary is minimized. Studies show that while all three methods have been able to identify the parameters well, the GA method produces less error and has a better performance in this field.

In this study, a 4×4 square network structure made of titanium has been optimized under tensile force using relevant parameters. The network structure is a quadrilateral structure with a side length of L and ϴ, and the fracture order of the walls has been compared using MATLAB software and simulation with Abaqus software, and the results of the fracture order of the structure match each other. In the present study, the objective function in optimization is to increase energy absorption and minimize the maximum stress, and the effect of parameters such as side lengths and various angles in this structure has been investigated. 100 different cases have been obtained for values of L and ϴ with output of area under the curve (energy absorbed) and maximum stress and strain using MATLAB software. With input data (L and ϴ) and output data (energy absorbed and maximum stress), a neural network has been trained and a regression model has been used in the neural network to achieve a prediction accuracy of over 99%, which is a high level of accuracy. The relationship function between input and output of the neural network has been obtained using MATLAB software, and the optimization of this 4×4 network structure has been carried out using the genetic algorithm. The objective function in this study is to increase energy absorption and minimize the maximum stress so that the network structure has the highest strength considering the examined parameters.

Laser shock peening is a surface optimization operation that leads to the improvement of mechanical properties such as increasing fatigue strength, surface hardness and tensile strength. This improvement of properties can be attributed to the creation of residual stress and cold work done on the surface. In this new method, which is considered as an alternative to the methods of peening and ultrasonic peening waves, there are many influential factors such as power density, percentage of overlap, type of protective layer and number of shocks, etc. In this research, Al2014-T6 alloy, which is widely used in aviation industries, including aircraft wheels, has been subjected to shock peening in order to increase its strength and fatigue life. Single, triple and quintuple shock processes were applied on this alloy to investigate the effect of different shock modes. Next, the amount of residual stress was analyzed with the help of X-ray diffraction analysis and changes in surface roughness by atomic force microscope, and then fatigue, tensile and microhardness tests were performed on the part. The results of the experiments show that with the increase in the number of times of laser shock and under the condition of no melting and surface destruction, the residual compressive stress increases, which leads to a 300% increase in fatigue life and a 25% increase in microhardness of the surface. It was also found that in addition to optimizing the parameters, increasing the shock frequency can also change the surface roughness and tensile strength.

Today, the use of ceramics and hard alloys in advanced industries has led to the creation of new methods such as electric discharge machining in order to reduce the disadvantages of traditional methods of chipping these materials. In turn, these methods also have defects, such as the quality of the machining surface, which in this paper has been tried to solve some of them by using an external alternating magnetic field and conducting practical tests on Inconel 718 hard alloy. In this paper, a Helmholtz coil is proposed to create an external magnetic field using an alternating current around the area of the electric discharge process. In the traditional and proposed method, the radius of the plasma channel is modeled mathematically and numerically, and experimental tests are defined to validate the theoretical results. Comparison of surface uniformity (morphology) and surface roughness (Ra) are considered as effective parameters between the traditional method and the proposed method. The plasma channel is assumed to be cylindrical. A roughness meter is used to control surface roughness. The results of mathematical-numerical modeling show a 10% reduction in the diameter of the plasma channel. According to the obtained results, the amount of surface roughness (Ra) has decreased in fixed times. The basis of validation of the proposed method is to compare the output parameters of machining surface quality in practical tests.