a. darvizeh
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In this study, at first, the dynamic progressive failure of Glass-Fiber-Reinforced aluminum laminates (GLARE) under low-energy impact with intra laminar damage models implementing strain-based damage evolution laws, Puck failure criteria using ABAQUS-VUMAT,were modeled. For interface delamination, bilinear cohesive model; and for aluminum layers the Johnson-Cook model was implemented;and the fatigue life of the fiber metal laminates of GLARE subjected to impact was obtained; and the numerical and experimental results of the model were compared with each other. With regard to the very good match betweenthe numerical and experimental results, the results of the finite element model were generalized and expanded, and with the use of the multilayer neural network, the numerical model was extracted and then, by applying the meta-innovative algorithm, the maximum fatigue life of GLARE was determined atthe highest level with very low-velocity impact,and the best configuration of three-layer GLARE was selected.The findings indicated that the best configuration of hybrid composite GLARE based on conventional commercial laminates that can tolerate low-velocity impacts with 18J impact energy and a 349MPa fatigue load with a frequency of 10Hz was [Al/0-90-90-0/Al/0-90-0/Al/0-90-90-0/Al] with 13016 cycle lifetime.
Keywords: GLARE, Fatigue life, multilayer neural network, Genetic Algorithm -
In this paper, a new approach is proposed for stress state - dependent flow localization in bifurcation failure model bounded through ductile damage in dynamically loaded sheets. Onset of localized necking is considered in phenomenological way for different strain rates to draw the forming limit diagram (FLD). Using a strain metal hardening exponent in the Vertex theory related to the strain rate helps investigate rate- dependent metal forming limits. Besides, the paper utilizes the model of ductile damage as a function of strain condition, stress states (triaxiality and Lode parameters), and the symbols of stiffness strain to predict the onset of the necking. It is worth noting that updated level of elasticity modulus in the plastic deforming is attributed as an essential index for the ductile damage measuring. According to original formulations, a UMAT subroutine is developed in the finite element simulation by ABAQUS code to analyze and connect the related constitutive models. Results reveal that the FLD levels increase for St 13 material through enhancing the strain rate.
Keywords: Ductile damage, Stress State, Strain rate, Forming Limit, Localized necking -
In this paper, the extended finite element method (XFEM) is employed to investigate the statics and vibration problems of cracked isotropic bars and beams. Three kinds of elements namely the standard, the blended and the enriched elements are utilized to discretize the structure and model cracks. Two techniques referred as the increase of the number of Gauss integration points and the rectangle sub-grid are applied to refine the integration within the blended and enriched elements of the beam in which the priority of the developed rectangle sub-grid technique is identified. The stiffness and the mass matrices of the beam are extended by considering the Heaviside and the crack tip functions. In a plane stress analysis, the effects of various crack positions and depths, different boundary conditions and other geometric parameters on the displacement and the stress contours are detected. Moreover, in a free vibration analysis, changes of the natural frequencies and the mode shapes due to the aforementioned effects are determined.Keywords: Extended finite element method, Statics, vibration, Cracked bars, beams, Increasing Gauss integration points, Rectangle sub-grid
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Car body lightening and crashworthiness are two important objectives of car design. Due to their excellent performance, composite materials are extensively used in the car industries. In addition, reducing the weight of vehicle is effective in decreasing the fuel consumption. Hat shape energy absorber is used in car’s doors for side impact protection.The aim of these numerical models and experimental tests is to unveil some important fact about using composite materials in hat shape energy absorber and also show the effect of orientation angles on the amount of energy absorption. The effects of different orientation angles on crushing behavior of hat shape structure are presented.
Keywords: Crash, Composite materials, Side impact, Hat shape structure, Experimental test
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