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In this paper a new approach for forming sheet metals by explosion of gas mixtures is presented. As the sheet metal shapes by the impact and pressure resulted from the explosion, it undergoes through a plastic deformation phase. Testing apparatus which is built for the first time in Iran, consists of a thick-walled cylinder (expolsion chamber), various dies for shaping, and measuring instruments. Unlike techniques used in conventional systems, in this method, the wave impact acts as the male part of the die to form and produce different engineering components. Experimental results presented show the effect of various parameters such as thickness, boundary conditions, and the material type of the work-piece, also the percentage of gas mixture on the distribution of thickness/circumferential strain in the work-piece. Furthermore, an analytical model based on the plastic work calculations for the sheet metal deformation is presented.

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This paper presents a finite element solution for the static analysis of a multi-layers beam with and without piezoelectric layers. The beam is under large deformation. The virtual work principle and the Lagrangian update method (LUM) have been employed to study the static behavior of piezoelectric beams. Four-nodes element with two displacement degrees of freedom and one electrical degree of freedom has been used in this analysis. Finally, in order to prove the validity of the presented formulation and the solving process, the results are compared with the other available data.

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In this paper, with the assumption of constant material properties, the nonlinear behavior of beams is studied using the finite element method. To this end, two approaches are represented: in the first approach, the beam is modeled by one dimensional elements of second order that is formulated according to continuum mechanics relationships based on the Lagrangian strategy, while in the second approach based on the Eulerian strategy the nonlinear behavior of the beam is investigated by making use of two dimensional elements. In both approaches, the second configuration, strains and stresses in the beam are obtained via the calculation of deformation gradient

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Forasmuch as, transition metal dichalcogenides (TMDs) are robust nanomaterials to sustain large strains without fracture, their application in new pliable electronic nanodevices is so appealing. Of these nanomaterials is tungsten disulfide which has specific electrical, optical and sensor properties; and due to possessing a non-planar structure, shows interesting responses under different plane strains. This investigation explores the mechanical properties of a monolayer tungsten disulfide (WS2) such as Young's modulus, bulk modulus, shear modulus and Poisson's ratio by applying the density functional theory (DFT) calculations based on the generalized gradient approximation (GGA). The results demonstrate that elastic properties of WS2 are less than those of graphene and its analogous inorganic hexagonal boron-nitride (h-BN) nanosheets. Unlikely, Poisson's ratio is calculated higher than that of graphene and h-BN nanosheets. It is observed that, due to the special structure of WS2, the thickness of nanosheet (distance between S-S atoms), bond length of W-S and the angle S-W-S change under different kinds of strains. Also, in the case of biaxial strain, the amount of variations in bond length, thickness and bending angle is higher than that in the cases of uniaxial and shear strain.

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In this paper, a scanning electron microscope (SEM) is used for microstructural investigations of a woodlouse shell. Finite element (FE) method is employed to study the dynamic behavior of the shell subjected to the impact of a cone-shaped projectile. Despite of small thickness, the shell, as a composite material, enables the insect to bear large external forces. The woodlouse is also able to roll up into a complete sphere to protect itself from danger. In order to study this defense mechanism, the external loads are applied to the shell in different configurations: when the shell is in (1) normal and (2) rolled-up forms. The simulations are performed at different velocities and at different impact angles. Comparisons of the results obtained from different simulations indicate that the defense mechanism of the woodlouse has an important role in decreasing the stress concentrations. Indeed, it is a defense mechanism which effectively increases the load-bearing capacity of the insect shell. The results of the present research may be useful in the design and manufacture of modern engineering structures with a high strength to weight ratio.

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Axially moving beams are extensively involved in various industries and have significant importance in many mechanical engineering problems. In this paper, the nonlinear forced vibrations of axially moving beam under harmonic force and thermal environment have been studied. In order to considering the effects of transverse shear deformation and rotary inertia, the Timoshenko beam theory has been used to model the axially moving beam. The nonlinear governing equations are derived with the help of Hamilton’s principle. Then the equations and boundary conditions are discretized through generalized differential quadrature method (GDQ) and its differential matrix operators, and accordingly the partial differential equations are converted into the ordinary differential equations. To study the frequency response of the system, the harmonic balance method is used. Also the time responses of the axially moving beam are obtained by the Runge-Kutta method. In a case study, the effects of various parameters such as the axial speed, transverse force acting on the beam, damping coefficient and temperature change on the frequency responses of the axially moving beam with both end simply supported boundary conditions are discussed. The results show that the dynamic behavior of system is significantly affected by any of the mentioned factors.

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The aim of this study is to investigate analytical and experimental energy absorbing capacity for a hat shape structure with three different boundary conditions. Four layered unidirectional (UD) E-glass fiber /polyester resin was used to construct hat shape beam energy absorber. The length of the composite hat shape was 1m and the thickness was 3mm. Result shows good coloration between experimental energy absorption and the values obtained from the model. The best coloration between experimental and the model is related to [75,0,0,-75] fiber stacking configuration with 0.23% accuracy in clamp-free boundary condition, and the worst coloration between experimental and the model is related to [30,60,-30,-60] fiber stacking configuration with 19.88% accuracy in clamp-free boundary condition.

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This paper investigates the effects of constructional elements on the biomechanical behavior of desert locust hind wing. First, the microstructure of the insect wing is investigated using scanning electron microscope. The results of the scanning electron microscopy are used to develop finite element models of the wing with different constructional elements. The presented models are studied under the inertial and aerodynamic loads applied during flight and the obtained stresses and displacements are assessed. The results show that longitudinal veins, longitudinal and cross veins, corrugations, corrugations and longitudinal veins and finally a combination of corrugations and longitudinal and cross veins cause averagely 4, 25.75, 4.34, 184.54, 768.5 times decrease of the achieved principal stresses in comparison with a wing without the mentioned constructional elements. Constructional elements of the locust wing play an important role to uniform the pattern of stress distribution in the wing during flight. Further, the existence of the mentioned constructional elements causes a decrease in the variation of the stress within a stroke-cycle. In addition, it is shown that the inertia and aerodynamic forces have less effect on the wing deformation than the elastic ones. The results of this research may be helpful in the development of lightweight structures with high strength.

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In this paper, the behavior of copper and steel rectangular plates with clamped boundary conditions subjected to underwater explosion loading is investigated. Cavitation is a phenomenon that occurs in this process. During the cavitation, the total pressure of the explosion becomes zero, so that the governing equations of motion time will be different before and after the cavitation. As a result, in terms of analysis and design, the cavitation time is significant in studying the behavior of a rectangular plate at underwater explosive loading. To calculate the cavitation time, the equations of motion of a rectangular plate underwater explosive loading are derived first, based on Hamilton principle and variation method. Then, in order to obtain the forced response of the rectangular plate, the exact free vibration solution of the rectangular plate is derived for exact mode shapes. Then, the speed and generated stress of plate during cavitation time are calculated and compared with the yield stress of copper and steel rectangular plates. Using this method, one can distinguish the cavitation with in the elastic or plastic regimes. Results show that the cavitation time is on the order of microsecond.

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In this paper, plastic deformation of the clamped mild steel and aluminum circular plates subjected to different hydrodynamic impact loading conditions are investigated. Extensive experimental tests were carried out by using a drop hammer. The experimental results presented in terms of central deflection of the plates, deflection profiles, and strain distributions. The effect of different parameters such as material properties, plate thickness, stand off distance of hammer or the transfer energy were also investigated on behavior of deformation of plate. Analytical modeling was carried out using energy approach and introducing the deflection profile function based on observes result of experimental. In this model effect of strain rate, hoop strain, radius strain and also effects of bending strain energy and membrane strain energy have been inserted. Calculations of the cases indicate that the proposed analytical models are based on reasonable assumptions. So, this method can be used for study of plastic deformation of plates under dynamic loading. The agreement between analytical and experimental results indicates that new analytical approach presented in this work maybe successfully employed for prediction of central deflection in different hydrodynamic impact loading conditions.

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In this paper, the dynamic plastic buckling of axisymmetric circular cylindrical shells subjected to axial impact is investigated. The von Mises yield criterion is used for the elastic-plastic cylindrical shell made of linear strain hardening material in order to derive the constitutive relations between stress and strain increments. Nonlinear dynamic circular cylindrical shell equations are solved with the finite difference method for three types of boundary conditions and two types loading. Two types of loading are stationary cylindrical shells impacted axially and traveling cylindrical shells impacted on a rigid wall. The growth and improvement of axial and lateral strains and buckling shapes of cylindrical shells are investigated for different boundary and loading conditions, from the viewpoint of stress wave propagation. It is found that the total length of cylindrical shell is affected by the plastic deformation when the plastic wave reaches unimpacted end. Also it is found that shortening and energy absorption are independent of loading and boundary conditions. The buckling shapes are affected by loading and boundary conditions; also peak loads at impacted and unimpacted ends are affected by loading conditions and are independent of boundary conditions. The presented theoretical results are compared with some experimental results and good agreement is obtained.

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Nowadays, availability, durability, reliability, weight and strength, as the most important factors in optimum engineering design, are responsible for the widespread application of plates in the industry. Buckling in the elastic or elastoplastic regim is one of the phenomena that can be occurred in the axial compressive loading. Using Galerkin method on the basis of trigonometric shape functions, the elastoplastic dynamic buckling of a thin rectangular plate with different boundary conditions subjected to compression exponetiail pulse functions is investigated in this paper. Based on two theories of plasticity: deformation theory of plasticity (DT) with Hencky constitutive relations and incremental theory of plasticity (IT) with Prandtl-Reuss constitutive relations the equilibrium, stability and dynamic elastoplastic buckling equations are derived. Ramberg-Osgood stress-strain model is used to describe the elastoplastic material property of plate. The effects of symmetrical and asymmetrical boundary conditions, geometrical parameters of plate, force pulse amplitude, and type of plasticity theory on the velocity and deflection histories of plate are investigated. According to the dynamic response of plate the results obtained from DT are lower than those predicted through IT. The resistance against deformation for plate with clamped boundary condition is more than plate with simply supported boundary condition. Consequently, the adjacent points to clamped boundary condition have a lower velocity field than adjacent points to simply supported boundary condition.

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When a dynamic load passes a control volume of material as a shock wave, passing this wave through the control volume could cause different phases such as elastic and plastic. From the microscopic view, during phase change, material flow would be taken in control volume which includes mass, heat, energy, and momentum transport. Phase change in material causes a material discontinuity in the control volume. During the phase change process, mass, heat, energy, momentum transport and etc will occur and the equations governing these phenomena are called transport equations. In this article, for the first time, the governing equations of elastoplastic behavior of beam under dynamic load are extracted by using mass, energy and momentum transport equations. Using transport equations with non-physical variables in integral form will cause in employing discontinuity conditions in governing equations and eliminates the discontinuity condition. These equations are also used in continuously modeling of beam elastoplastic behavior under dynamic loading and a continuous model is presented. Finite element method is used to solve the transport equation with non-physical variable. Finally, the time history of stress, strain and velocity wave propagation along beam are presented in elastic and elastoplastic phases

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In this paper, the elastoplastic response of copper, steel and aluminum circular plates with clamped boundary conditions subjected to underwater explosion loading is investigated. Cavitation is a phenomenon that can be occurred for plates in the process of underwater explosion forming. The total pressure of the explosion becomes zero at the cavitation time, so that the governing equations of motion time will be different before and fter the cavitation. As a result, in terms of analysis and design, the cavitation time is significant in studying the behavior of a circular plate at underwater explosive loading. By appling the energy method and based on Hamilton principle and variation method the equations of motion of an underwater circular plate subjected to explosive loading are derived. Then, in order to obtain the forced response of the circular plate, the exact free vibration solution is derived to calculate the mode shapes. Then, the velocity and generated stress of plate during cavitation time are calculated and compared with the yield stress plates. Using this method, one can distinguish the cavitation with in the elastic or plastic regimes. By recognizing the time of cavitation in the range of elastic or plastic, the displacement and velocity field of plate are determined in duration of explosive loading. Results show that the cavitation time is on the order of microsecond. Depending on amount of charge mass and stand-off, the cavitation time may be occurred in elastic or plastic regime.

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Using molecular dynamics simulations, the structural properties and vibrational behavior of single- and double-walled carbon nanotubes (CNTs) under physical adsorption (functionalization) of Flavin Mononucleotide (FMN) biomolecule are analyzed and the effects of different boundary conditions, the weight percentage of FMN, radius and number of walls on the natural frequency are investigated. As the functionalized nanotubes mainly operate in aqueous environment, two different simulation environments, i.e. vacuum and aqueous environments, are considered. Considering the structural properties, increasing the weight percentage of FMN biomolecules results in linearly increasing the gyration radius. Also, it is observed that presence of water molecules expands the distribution of FMN molecules wrapped around CNTs compared to that of FMN molecules in vacuum. It is demonstrated that functionalization reduces the frequency of CNTs, depending on their boundary conditions in vacuum which is more considerable for fully clamped (CC) boundary conditions. Performing the simulations in aqueous environments demonstrates that, in the case of clamped-free (CF) boundary conditions, the frequency increases unlike that of CNTs with fully clamped and fully simply supported boundary conditions. The value of frequency shift increases by rising the weight percentage of FMN biomolecule. Moreover, it is observed that the frequency shifts of SWCNTs with bigger radius are more considerable, whereas the sensitivity of frequency shift to the weight percentage of FMN biomolecule reduces and this is more pronounced as the simulation environment is aqueous.

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In this work, an analytical micromechanical model based on unit-cell approach is used to study the effect of interphase on the non-linear viscoelastic response of multiphase polymer composites. The representative volume element of composite consists of three phases including unidirectional fibers, polymer matrix and fiber/matrix interphase. Perfect bonding conditions are applied between the constituents of composites. The Schapery viscoelastic constitutive equation is used to model the nonlinear viscoelastic matrix. Prediction of the presented micromechanical model for the creep response of polymer material and two-phase composites shows good agreement with available experimental data. Furthermore, the predicted overall elastic behavior of three-phase composites demonstrates close agreement with other numerical results available. The effects of material and thickness of interphase on the creep-recovery strain curves of three-phase composites are studied in details. Results show that the interphase thickness and material properties have significant effect on the creep-recovery strain responses of the three-phase composites under transverse loading. According to micromechanical modeling results, it is found that the interphase negligibly affects the nano-linear viscoelastic behavior of three-phase composites under axial loading. Effects of the different stress levels and the variation of fiber volume fraction on the creep-recovery strain curves of three-phase composites are also investigated.

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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, 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 new sheet metal forming process as incremental sheet forming and spinning forming, this is not perfectly true in Marciniak-Kuczyinski model to assume that sheet deformation occurs in the plane-stress state indispose there are normal compressive stress and through-thickness stress. In this type of forming processes, the obtained limit strains refer to improving the sheet forming. However, in researches the effects of through-thickness shear stresses, also known as out-of-plane shear, has been studied less. The generalized forming limit diagram is a great curve that includes all six components of the stress tensor. In this paper, the effect of normal comprehensive and through-thickness shear stresses on the limit strain AA6011 aluminum sheet using a modified M-K and the anisotropic Yield function, Hill 48 and by using numerical solutions of nonlinear equations, Newton-Raphson method. The first the forming limit diagram was drawn with the assumption that the through-thickness shear stresses and then the effects of normal comprehensive stress and through-thickness shear stress on the limit strains were proved and the generalized forming limit curves were obtained. The results show that forming limits can be increased significantly by both normal compressive stress and through-thickness shear stresses. Also, the effects of normal stress on increasing the formability of sheet compared with the effects of through-thickness shear stress is greater.