Papers by Author: M. Amidpour

Abstract: There are two approaches to design high energy absorbing materials and structures: one is to optimize the structures by using ordinary materials. The other is to design new energy absorbing materials. The efficiency of energy absorbing structures is continuously improved by developing various types of structural geometries and selecting appropriate energy absorbing materials like polymeric foams or metallic foams. Because of composite materials which are used in these kinds of structures, too many useful properties are achieved, for example, light weight, high energy absorption, high stiffness, fracture toughness. In this study, different composite sandwich structures are modeled by ABAQUS FE software. The model is validated by the results in existed literature. Different materials as core and as face sheets in the composite sandwich structure are investigated. Internal energy and displacement of the structure during the impact analysis in low velocity are calculated. By changing variables and parameters such as dimensions of the structure, different properties and sequences of the layers in the face sheets and different core materials, the optimum state of the structure for gaining the highest internal energy is determined. By increasing the size of the structure and using the stiffer fibers, the absorbed energy is increased. The effect of stiffer core in increasing absorbed energy is more significant. The layer sequencing does not affect any changes in the absorbed energy.

Abstract: It is well known that the crack growth rate fatigue and stress corrosion cracking can be approximated by a power function of the stress intensity factor. In this study, stress intensity factor for elliptical crack under the uniform tension in linear elastic fracture mechanics (LEFM) is investigated therefore for this purpose, a pressure vessel modeled by finite element. A crack modeled on the pressure vessel and then the stress intensity factor for crack propagation in different methods is evaluated. Finite element analysis calculates stress intensity factor in the values of the J-integral are based on the stress intensity factors, JK, and by evaluating the contour integral directly, JA. The stability of crack growth is considered so the ductile crack extension is determined by pursuing the equilibrium between loading and crack resistance. Using especial method of meshing caused to have accurate results. This method causes to decrease run time and considerable accuracy. Then stress intensity factor is calculated for different position of the crack such as crack front and then compared to each other.