Sharif Digital Repository

The constitutive modeling of material is clearly a keystone of successful quantitative solution possibilities. No finite element code will provide results of better quality than that of the constitutive equation implemented in it. In this study, a nonassociated three-invariant cap plasticity model is presented for material under compressive stress. Generalized single-cap plasticity is developed which is based on the hardening-softening material functions. The hardening functions are consisted of isotropic and kinematic parts. Using the definition of yield surface, material functions and nonlinear elastic behavior, as function of hardening-softening parameters, the constitutive elasto-plastic... 

In this paper, a methodology has been proposed for design of passive energy dissipation systems through active control theory. The passive control system is designed to achieve a structural response as close to that of active control system. It may be needed to reduce the stiffness of the original structure at some locations to reduce the acceleration response. Then, to compensate for the resulting increased interstory drifts, viscous fluid dampers are added to the structure at their optimum locations. The optimal distribution of dampers and the locations with reduced stiffness are obtained using the LQR active control algorithm. It is shown that the response of a properly-designed... 

Production of nanocrystalline (under 100nm) or submicron materials (100-1000nm), has been created to one of the most important problems in engineering. A well-known method to create Ultra-Fined Grains (UFG) is imposing high strains to metals in order to break the structure. Among lots of ways forproducing UFG metals, Equal Channel Angular Pressing (ECAP) is one of the most famous and common ways. On the other hand, Shot Peening has been being used for a long time to improve mechanical properties of metals by introducing nanocrystalline layer at the surface of specimen. The aim of the work, is investigation of the effect of combination of ECAP and Shot Peening on High Cycle Fatigue of 6082... 

The behavior of soil-structure interface plays an important role in the static and dynamic analysis of soil-structure systems. Development of new materials such as polymer concrete requires an understanding of the behavior and their interaction with other materials. In this investigation, the interface behavior between polymer concrete and ordinary concrete with sand was studied using interface direct shear tests. In order to find optimum content of epoxy resin for polymer concrete, a series of tensile and compressive tests were conducted. To study the mechanical properties of concretes-sand interfaces behavior two series of interface direct shear tests were conducted at three different... 

Recycling of asphalt pavements has received much attention in recent years for its environmental and economical benefits. Because of increase in costs of raw materials and energy carriers, reuse of a high portion of reclaimed asphalt pavements (RAP) eliminates an enormous amount of waste and reduces the cost of hot-mix asphalt (HMA) mixtures. There are some problems in high-RAP mixtures such as high content of fine aggregate and filler, low temperature cracking potential because of higher stiffness of RAP binder, and low mixture workability. In this research, RAP fractionation was used to sort out and eliminate fine aggregate and filler. An organic-based softening agent was used to improve... 

The new generation of advanced high-strength steels use in the automotive industry cause resistance spot welding study and their failure characteristics during static and dynamic loading are important. In this study, the relationship among microstructure, failure mode and mechanical properties are investigate during similar and dissimilar DP980 and MS1400 jointing advanced high-strength steels resistance spot welding. To search for micro and macro structural changes, the optical microscope, stereographic microscope and scanning electron microscope were used. Micro-hardness test, tensile shear test and Cross tension test to evaluate the mechanical properties were conducted. As well as... 

In this study, behavior of softening after hot tensile and hot rolling processes in isothermal and non-isothermal conditions in AA5083 Aluminium alloy has been simulated using cellular automata. Also effect of temperature and strain rate in hot tensile test and effect of temperature and strain in hot rolling has been investigated. First distribution of temperature in material using the finite element method computed and used as initial temperature in CA and computing the static recovery in hot tensile. Also for hot rolling, computing static recovery and CA are used for initial temperature in ABAQUS. For investigating effect of dynamic recovery and recrystallization, the neural network has... 

The use of conventional multi-scale models for materials that exhibit softening behavior is not possible due to the phenomenon of localization, because the fundamental assumptions of homogenization are no longer satisfying around the localization region, and therefore the macro-scale results depend on the size of the representative volume element and the macro-scale mesh discretization. Also, if the finite elements mesh be fine enough, the solution does not converge to acceptable physical values. This research concerns the multi-scale study of failure and proposes an appropriate method for computational homogenization of that. The main idea is to apply the enhanced homogenization method to...