Sharif Digital Repository

A set of complementary experiments are used for the first time to elucidate the interrelation between the mechanical properties, the strain field, and the free volume evolution during non-homogenous compression of aglassy polymer. Two sets of quenched and annealed polystyrene samples, having different free volume histories, are notched and exposed to compression. The variation of both the strain field and the free volume are measured on a microscopic scale via digital image correlation in case of strain and Doppler broadening spectroscopy of positron annihilation line in case of free volume measurements. Eventually, the interplay between the local evolution of free-volume, the local strain... 

In the present work, the process of equal channel angular pressing of dispersion strengthened Cu-1̇1 wt-%Al2O3 containing nanometric alumina particles was investigated by means of mathematical modelling and experimental testing. Through the modelling, deformation parameters such as hydrostatic pressure distribution and strain field were determined, and the effect of deformation path on these parameters was estimated. Equal channel angular pressing as well as mechanical and microstructural evaluations were also conducted to assess mechanical properties, grain structure and void volume fraction after deformation in different routes. The results indicate that distributions of plastic strain and... 

In this work, softening kinetics after cold rolling has been simulated using a coupled finite element-cellular automata model. Firstly, a two-dimensional rigid plastic finite element analysis has been developed to assess strain field and the stored energy accumulation during cold rolling as well as the initial condition of the mesoscopic model. Then, the cellular automata scheme has been employed to calculate the progress of static recrystallization at a given temperature while a dislocation-base model was simultaneously utilized to consider the effect of recovery on static softening process and final microstructures. The model has been examined on isothermal annealing of cold rolled AA5052... 

Utilizing the Finite Element Method (FEM), the strain field in the radial forging process of tube is calculated at different process conditions and compared with the experimental results achieved using the microhardness test. The effect of various process parameters such as friction, axial feed, back push and front pull forces and die angles on the strain field are investigated. Using the results of the analysis, it is shown that the deformation inhomogeneity, introduced by an Inhomogeneity Factor (IF), is maximum in the inner zone of tube, while the minimum and the maximum effective strains are appeared at the inner zone of tube and about the core of the tube thickness, respectively. Also,... 

In this paper the previous velocity field proposed by the authors for the prediction of strain field and deformation load of circular cross section billet in ECAE process has been extended to take into account the deformation behavior of bimetal circular billet in the same process. Accordingly, using Bezier method, as a robust method for determining the geometry of the streamlines, the strain field developed in the circular bimetal billet is calculated. Then, based on the kinematically admissible velocity and strain fields and using the upper bound theorem the ECAE load is predicted. It was found that at constant inner corner angle of ECAE die, with decreasing of outer curve corner the... 

In this research in order to predict the strain distribution and extrusion load in equal channel angular extrusion (ECAE) process of circular cross section a new three dimensional kinematically admissible velocity field has been developed based on Bezier formulation. The strain distribution in deformation zone and the effects of various terms on extrusion load were determined. The results were compared both with the experimental and numerically predicted results reported in the literature. It was found that extrusion pressure decreases with increasing both the die angle and the outer curved corner angle and increases with increasing the friction coefficient. Also, it was exhibited that... 

A semi-analytical three-dimensional elasticity solution for rotating functionally graded disks for both of hollow and solid disks is presented. The aim is to generalize an available two-dimensional plane-stress solution to a three-dimensional one. Although for the thin disks problems the two-dimensional solution provides appropriate results, for the thick disks, a three-dimensional elasticity solution should be considered to avoid poor results. It is shown that although the plane-stress solution satisfies all the governing three-dimensional equations of motion and boundary conditions, it fails to give a compatible three-dimensional strain field. A valid three-dimensional solution has been... 

Displacement and strain fields of a screw dislocation in a nanowire are considered within the theory of gradient elasticity. The gradient solution of the corresponding boundary value problem is derived and discussed in detail. It is shown that the dislocation fields do not contain classical jumps and singularities at the dislocation line. The maximum values of the dislocation displacement and elastic strain strongly depend on both the dislocation position and nanowire radius, thus demonstrating a nonclassical size effect. © 2008 Acta Materialia Inc  

To investigate the effect of 3D and 2D deformations on flattened wires, the effective strain fields of flat rolled and sidepressed wires are predicted using the combined finite and slab element method (FSEM) and two-dimensional finite element method (TDFEM), respectively. The validity of the calculated strain fields are verified using the Vickers microhardness test. Utilizing the calculated strain fields, the strain inhomogeneity of the flat rolled and sidepressed wires are investigated. To assess the effects of height to width ratio and frictional condition on the strain inhomogeneity, an inhomogeneity factor (IF) is defined. The results show that for both the flat rolled and sidepressed... 

In this paper, in order to investigate the creation of macroscopic shear bands, due to material flow tracks in the cross section of a wire after flat rolling, the combined Finite and Slab Element Method (FSEM) is used. The effective strain field is predicted for different reductions in height. The validity of the method is assessed by performing the Vickers microhardness measurements on the cross section of the flattened wire. It is found that the FSEM and microhardness results show the minimum and the maximum effective strains at the round edge and the center of the flattened wire, respectively. Also, the results indicate two bands of maximum effective strain in the cross section of the... 

Traumatic brain injury (TBI) has long been known as one of the most anonymous reasons for death around the world. A presentation of a model of what happens in the process has been under study for many years; and yet it remains a question due to physiological, geometrical and computational complications. Although the facilities for soft tissue modeling have improved and the precise CT-imaging of human head has revealed novel details of brain, skull and the interface (the meninges), a comprehensive FEM model of TBI is still being studied. This study aims to present an optimized model of human head including the brain, skull, and the meninges after a comprehensive study of the previous models.... 

In this paper, free vibration of a fiber reinforced composite cylinder in which volume fraction of its fibers vary longitudinally, is studied using a semi-analytical method. The distribution of volume fraction of fiber in base matrix is based on power law model. A micromechanical model is employed to represent its mechanical properties including elastic and physical properties of this composite cylinder. In addition, kinematically the first order shear deformation shell theory is employed for strain field. Then, weak form formulation and spatial approximations of variables are utilized to discretize the equations of motion. Different problems are solved in which primarily the validity of the...