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Prediction of critical process parameters which causes bursting and its location in warm tube hydroforming is a key factor in hydroforming parts design. In this paper, ductile fracture criteria have been modified so that effect of variation of temperature and strain rate on fracture is considered in forming of aluminum AA6063 tubes. Calibration of modified ductile fracture criteria has been performed using uniaxial tension tests at different temperatures and strain rates. Also, fracture strain and fracture work have been obtained as functions of Zener-Holloman parameter. Tube hydroforming process of a square part has been simulated at high temperatures in Abaqus software and loading curves with various axial feeds have been used to deform the tube. Then, the formed corner radius before bursting has been predicted using modified fracture criteria. A subroutine has been written for using modified fracture criteria. A warm tube hydroforming setup has been fabricated and prediction of modified ductile fracture criteria is compared with experimental results at various temperatures. Results show that modified criteria determine the location of bursting well. Maximum of thinning occurs in transition zone which the tube loses its contact with die cavity. Also, modified Ayada criterion, rather than other criteria, predicts corner radius with little error at high temperatures. Thus, because of its precise prediction, modified Ayada criterion can be used to predict the bursting of aluminum tubes at elevated temperatures.

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Tube hydroforming is a process which is considered to produce integrated and seamless parts in recent years. The numerical prediction of tearing to design the right equipment in this process is important. In this study, the formability of 304 stainless steel tube by free bulge test was experimentally and numerically evaluated to determine the forming limit diagram. The Gurson- Tvergaard- Needleman (GTN) is a micromechanical model to predict ductile fracture of metals. In order to determine the defining parameters of the GTN damage model, the experimental tensile test of the standard sample and the finite element simulation using ABAQUS software was performed. Using this criterion in the ABAQUS software and comparing the force-displacement diagram obtained from the experimental tensile test and the finite element simulation, the parameters of the GTN model was obtained by the inverse method. Then, the geometrical parameters of the die in the free bulge hydroforming process were investigated by the GTN ductile fracture criterion and the forming limit diagram of the 304 stainless steel tube was numerically obtained. The experimental tests were also carried out to verify the results of the finite element simulation. It’s shown an acceptable agreement

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In this research, a general mixed mode I/II fracture criterion is developed for fracture investigation of orthotropic materials. Various experimental tests show that cracks always propagate in an isotropic medium and along fiber direction in orthotropic materials. With a novel material model titled an Equivalent Reinforced Isotropic Model (ERIM), fracture criterion can be extended for investigation of fracture in orthotropic materials. This inspires that fracture in orthotropic materials follows the fracture mechanism in isotropic materials. This new criterion is developed based on extension of MTS which is widely used for isotropic materials. Also in this research the effects of T-stress in fracture of some specimens has been studied. A comparison between available experimental observations and theoretical estimation implies on capability of developed criterion for predicting both crack propagation direction and fracture instance, wherein the achieved fracture limit curves are also compatible with fracture mechanism of orthotic materials. It is also shown that non-singular T-stress term has a significant impact on orthotropic material failure, especially when the second mode is dominant mode. It is shown that unlike isotropic materials, fracture toughness of orthotic materials in mode I (K_IC) cannot be introduced as the maximum load bearing capacity and thus new fracture mechanics property, named here as maximum orthotropic fracture toughness in mode I (├ K_IC ┤|ortho) is defined. Considering ease of access, wood is used as experimental specimen for the purpose of comparing the results.

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The big deformation of composite structures under dynamic loads is one of the most disadvantages of these structures that cause to loss of stiffness of them. The using of fiber metal laminated shell that named FML in abbreviation is one of the ways to decrease the adverse effect of dynamic load. In this study the optimum fiber orientation of composite layers of the FML circular cylindrical shells are determined to more decrease the adverse effect of dynamic loads. For this purpose the fiber orientation of composite layers of the FML circular cylindrical shells are changed frequently and each cases being subjected to axial compressive load and with use of ABAQUS program the tension of all composite layers are calculated for all cases. Then with use of MATLAB program the fiber orientation that cause to maximum stiffness based on maximum tension fracture criterion is selected. The free vibration analysis is used for determination the accuracy and performance of design process. The results of free vibration analyses show that determination of the optimum fiber orientation cause to improvement of the FML shell natural frequency. Energy method and high order shear deformation theory is used to define the equation of motion. Full Calculus method is used for optimization in order to apply the exact result.