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In this paper, the internal inversion process of metallic cylindrical shells under dynamic axial loading is investigated experimentally and numerically. Experimental tests are performed on the steel tubes in a gas gun and the required force for internal inversion is obtained using the measurement system of impact loadings. Also, numerical analysis is carried out by the finite element software ABAQUS and the accuracy of simulated models are validated with the experimental results. In this paper, all geometrical properties of the tubes and die are assumed to be constant and the effect of the projectile mass and velocity is investigated on the shortening and energy absorption of the tubes which are affected by axial impact in the internal inversion process. Therefore the projectile is shot directly to the specimen with different masses and velocities. It is observed that if the projectile mass remains constant, increasing in the impact velocity has almost no effect on the constant inversion load and just increase the tube displacement but if the impact velocity remains constant, increasing the amount of projectile mass causes increasing in the constant inversion load besides of increasing in tube displacement. Comparing the results of numerical simulations with the experimental results shows a good agreement between them.

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In this paper, in order to build T shaped tube by hydroforming method, the drop hammer system is used which leads to the hydrodynamic load. To form the first piece as the die configuration, the hydraulic internal pressure and axial feeding is required, and in the study of this process a source of energy should be used in two ways. According to mentioned load path, the die designed to get the impact of free fall weight by pistons on the die, and it makes the hydraulic pressure. by putting the punches on both sides of the tube, axial feeding takes place with receiving the hydraulic pressure of Intermediate fluid, and the internal pressure provides with transmission the fluid from the middle hole of the punches. It is worth noting that copper and aluminum tubes have been analyzed in experimental tests. To check the numerical analysis of final pieces and improve the quality of shaping, the finite element software ABAQUS is used. The simulation model of forming T shaped tube has been evaluated dynamically by considering the effect of strain rate and mechanical properties of tube material. The results of tests show that to have favorable deformation, all the input parameters such as the kinetic energy, fluid column, sealing, Lubrication, gender and the thickness of tube should be proportional together. Also in this study, the height of the bulge has been analyzed due to the thickness distribution, axial displacement and surface embrace.

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In this paper, the behavior of cylindrical shells with uniform thickness and functionally graded thickness distributions subjected to axial quasi-static loading is investigated experimentally and subjected to axial impact is investigated experimentally and numerically. Steel cylindrical shells with uniform thickness and functionally graded thickness distributions have same inner diameter, length and weight. Cylindrical shells are impacted by the drop hammer apparatus and experimental axial force-time curves are obtained by using a load cell; in addition, impact simulations are done by Abaqus finite element software. The effect of thickness distributions on the shortening, energy absorption, buckling shape and axial force-time curve of cylindrical shells is investigated. It is found that for axial quasi-static loading, a change in thickness distribution of cylindrical shell is able to convert the buckling shape from mixed buckling (a combination of axisymmetric and diamond modes) to progressive buckling, also for axial impact loading, a change in thickness distribution of cylindrical shell can affect the number of complete folds. The studies also suggest that at same impact energy, functionally graded thickness distribution cylindrical shell compared with uniform thickness distribution cylindrical shell absorbs approximately the same energy with more shortening and transforms less mean load and peak load to under protected specimen, thus, functionally graded thickness distribution cylindrical shell is a better energy absorption specimen. It is found that there is a good agreement between the experimental and numerical results.

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In this paper investigate the effects of friction stir pre-mechanical processing on damage evolution of 7075-T6 aluminum alloy by implementation of stress state dependent damage model which described in phenomenological way. For this purpose, specimens with special geometry were designed from sheet with friction stir pre-mechanical processing and without it of mentioned alloy. Each of these specimens demonstrate special stress state at fracture location in uniaxial tensile test. Material parameters determine for two different fracture initiation models, Xue and Hosford-Coulomb by using experimental result. By using each of these models, plastic strain to fracture surface obtained at stress state parameters for pre-mechanical friction stir condition and without it which can use to specify strain plastic to fracture for different stress state at different pre-mechanical friction stir and without it for this material. Also a phenomenological stress state dependent damage model and evolution of it investigated for this material at different pre-mechanical friction stir and without it by using these models. The experimental results show increase of plastic strain of material because of pre-mechanical friction stir and damage model show decrease of evolution of ductile damage because of this pre-mechanical processing. Also by comparing of damage result which obtained by using two different fracture initiation, Xue and Hosford-Coulomb conclude that using Xue model has better result than Hosford-Coulomb model and this model has more reliability to predict evolution of internal damage for this material and this model fracture surface has good compatibility with experimental results.

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In the present work, experimental and numerical results of the effects of different pressure curve on the thickness variation of sheet metal and distribution of radius and hoop strain for effective stress-strain curve have been presented. A series of experiments are carried out using a hydroforming apparatus by exerting different pressure curves including pendulous, steeped, saw and continuous. In each series, the effect of changes in pressure curve on thickness distribution was quantitatively measured. Different pressure curves such as continuous, stepped, and pendulous was produced in experiments. The ABACUS software was implemented to simulate the effect of changes in pressure curve. A good agreement between the experimental and numerical results was observed. The results show that stepped pressure produces more uniform distribution in sheet metal thickness. Mechanical behavior of sheet metal during plastic deformation phase under stepped pressure, produced satisfactory results, and using this type of pressure could control the effects of friction between the die surface and sheet metal specimen much better. Also, constant time duration of pressure pulses in stepped and pendulous curves leads to decreasing of maximum pressure needed for deformation of sheets.

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In the present paper, forming of clamped triangular plates by means of water has been investigated. The plates were made of st-12 and had the thicknesses of 1 and 2 millimeters. The experimental tests were performed at the impact laboratory of Guilan University using drop hammer system. Various aspects of numerical investigation were simulated by Abaqus software. As mentioned above, using drop hammer system as a hydrodynamic loading tool and carrying out different empirical tests in this study, the effect of factors such as thickness, standoff distance of hammer and its weight, i.e. the applied momentum to the system have been studied. In the numerical simulations, the deformations of triangular plates were simulated by smoothed-particle hydrodynamics method. Also, the Fluid-Structure Interaction was considered for simulating the fluid phase and the plate deformation was modeled using finite element method in the form of coupled SPH/FEM. Furthermore, the ultimate deformation, stress distribution, stress concentration of plates and position of maximum deformation on triangular plate have been investigated. Agreement between the obtained data from numerical simulations and experiments guarantied the accuracy of simulations.

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At present paper, an equivalent model with different dimensions and also with different dimensions and material in comparison with main body for strain rate sensitive structures subjected to high rate loading is presented by using the novel finite similitude method. The finite similitude method provides performing a test on the model instead of the original sample. This method is used to obtain the properties of model and to reverse the obtained results for model to main body by using the principles of nature (the law of conservation of mass, the law of conservation of momentum, the law of conservation of energy and the law of conservation of entropy) which is always true for any system. The relationships for both pure dimensional and simultaneously dimensional/material scaling of strain rate sensitive structures are presented. To evaluate the efficiency of the proposed relationships, the numerical results are obtained for impacted circular plates. It should be mentioned that the numerical results are obtained by using the finite element software LS-Dyna in which the strain rate effects are considered into account by using the Cowper-Symonds and Johnson-Cook constitutive equations. The results indicate that the scaled plate to one tenth of its original dimensions and also made of different material in comparison with original plate predicts the response characteristics of the original plate with a very good accuracy.