فهرست مطالب یوسف طراز جمشیدی

Porous materials especially metallic foams are novel materials with high energy absorption and strength to weight ratio capability. In the present paper we investigate quasi-static uniaxial compression and crushing behavior of closed-cell graded aluminum foams and foam-filled tubes, both numerically and experimentally. To model the mentioned specimens, we place cubes with several densities and strengths to generate functionally graded specimens. Specimens are considered as to be graded with two and three layers and non-graded single layer, with and without tubes. Various standard uniaxial compression experiences are conducted for numerical model calibration and validation and also for non-linear mechanical properties and hardening characterization. To enhance strength and energy absorption capability and also tailoring purpose, we layout the cubic foams in tubes with square profile. The 3D Voronoi diagrams approach is manipulated to model stochastic foam microstructure. Also Novel unit cell is proposed based upon Kelvin cell. We implement the hybrid finite element analysis and Voronoi diagram using Python script and Abaqus 2017 commercial FEM-based code for more convenient modeling and efficient analysis. Finally, and after numerical model calibrations, numerical and experimental results showed good agreement.

A numerical and experimental low-velocity impact behavior of sandwich plates have been presently studied with regard to the compressibility and viscoelasticity features of their cores. Face sheets were assumed to be anisotropic composites or isotropic aluminum materials and a viscoelastic behavior has been considered for core. The boundary conditions are assumed to be simply supported or rigid. Abaqus, as FEM software, and its python script programming feature, have been used to model the specimens. To model hyper-viscoelastic nonlinear behavior of the core, Ogden hyper-foam elasticity and Prony series approach are manipulated. To solve the numerical problem, dynamic explicit solver option with sufficient solving amplitude has been used. Prony series have been used to model the core time-dependent behavior. In conjunction with a simple indentation experiment, FEM used to formulate a novel method for finding the Prony series coefficients. By performing some low-velocity impact experiments, the impact force and displacement of the composite sandwich plates have been investigated. The results indicate that increasing the structural damping increases the contact time and missing energy and decreases the stored energy of the system. The structures with composite face sheets have a minimum ratio of upper face sheet displacement to lower face sheet displacement in comparison to those with the isotropic face sheets. Impact behavior of isotropic face sheet specimens are more flattened than that of the composite face sheets. In addition, the specific energy stored in the sandwich plates with composite face sheets, on different supports, is greater than that stored in the aluminum face sheets.