Iranian Journal of Materials Forming
Volume:1 Issue: 2, Autumn 2014

In this research, the bending analysis of rectangular nanoplates subjected to mechanical loading is investigated. For this purpose, the strain gradient elasticity theory with one gradient parameter is presented to study the nanoplates. From the best knowledge of authors, it is the first time that the exponential shear deformation formulation based on strain gradient elasticity theory is carried out. An analytical solution for static analysis of rectangular plates is obtained to solve the governing equations and boundary conditions. The suggested model is justified by a very good agreement between the results given by the present model and available data. Additionally, the effects of different parameters such as internal length scale parameter, length to thickness ratio and aspect ratio on the numerical results are also investigated. It is hoped that the present methodology lead to other models for static and dynamic analysis of rectangular nano structures with considering small scale effects.

Frictional shear stress is usually determined by utilizing the coefficient of friction or the constant friction factor models. The present study deals with finite element analysis of double cup extrusion process to determine the relationship between constant friction factor (m) and coefficient of friction (µ), since the metal flow in this process is very sensitive to frictional conditions. Therefore, the Finite Element-Code Deform 2D is used which is capable of utilizing both µ and m. According to this analysis a new equation between constant friction factor (m) and coefficient of friction (µ) is suggested. Moreover, in order to evaluate the suggested equation and to compare it with the pervious relationship, finite element analysis of barrel-compression test is carried out. Finite element results indicate that the new equation can accurately predict the relation between m and its equivalent μ value. The importance of converting these factors to each other is specially highlighted to introduce the frictional conditions in some professional and commercial finite element softwares.

The brass tubes with foam cores of AlSi7SiC3, AlSi7SiC3Fe1 and AlSi7SiC3Fe3 were produced as the crush-boxes with circle and square cross-section. Then axial compressive behavior and energy absorption capability of the foam-filled tubes were investigated during the quasi-static progressive plastic buckling. The uniaxial compressive stress–strain curves of the foam-filled brass tubes exhibited that the compressive stress rose smoothly with the increase of the strain and no stress oscillations occurred in the plastic deformation region throughout the tests. The yield stress and the elastic modulus of the foam-filled brass tubes slightly decreased with increasing of the Fe wt. % in the foam cores. Also, with increasing of the Fe powder from 1wt. % to 3wt. %, the absorption energy of the foam-filled brass tubes decreased slightly dependent on the tubes cross-section. The strain-hardening exponent of the tubes with the Al7Si-3SiC-() foam cores were found to be lower than the tubes with the Al7Si-3SiC foam cores with no Fe. However, increasing the Fe powder from 1wt. % to 3wt. % caused that the strain-hardening to be approximately eliminated and the plastic deformation behavior tends to be approximated to an ideal-plastic behavior up to the densification strain. Results show all of the compression responses are due to the Micro and Macro-defects within the foams cellular structure as well as the tubes cross-section geometry .

In this work dynamic recrystallization behavior of AISI 403 martensitic stainless steel was studied using hot compression tests over temperature range of 900 C -1200 C and strain rate range of 0.001 s-1 - 1 s-1. The obtained flow curves showed that the hot compression behavior of the alloy is controlled by dynamic recrystallization. The flow stress and strain corresponding to the critical, peak and onset of steady state region were related to the Zener-Hollomon parameter using simple power equations. The variation of dynamic recrystallization fraction with strain showed that restoration kinetics is enhanced with increasing temperature and decreasing strain rate. The development of DRX was modeled using Avrami Kinetics equation. The equations proposed by Baragar and Cingara-McQueen were used to develop a new model capable of predicting the flow curves up to the onset of steady state flow region. This work softening is mainly controlled by the phenomenon dynamic recrystallization.

The static strain aging is a phenomenon that can change the mechanical properties of low carbon steels. Thus, the static strain aging behavior of low carbon steel wires after drawing process is studied. To do so, the wires are austenitized at different temperatures and cooled in different rates. Then the wires are drawn and aged at a specific temperature and time. Before and after aging of each drawn wire, the hardness distribution at its cross section is measured. The increase in hardness due to aging is called aging index. The results show that the hardness of drawn wire is increased from center to surface of its cross section. However, after aging the hardness is decreased from center to surface. In addition, with increasing the austenitizing temperature, the index is increased. Also, with increasing the cooling rate, the index is decreased. Moreover, the aging index is decreased from center to surface.

Accumulative roll bonding (ARB) was used to fabricate the Cu-Zn multilayer and Cu-Zn solid solution. A lamellar structure with the hardness of about 130 VHN was formed after eight ARB cycles. Following to the suitable heat treatment, a solid solution with a uniform microstructure and hardness of about 57 VHN was produced. The dominant wear mechanism in the ARB processed multilayer was found to be delamination and spalling while in the heat-treated sample was adhesion. The weight loss of the ARBed multilayer was higher due to the occurrence of spalling and formation of the cracks and cavities during the ARB. On the other hand, the friction coefficient and its undulation were lower, which was contributed to the lubricating effect of Zn and the higher hardness of the ARB processed multilayer. In the heat-treated sample, the ability to plastic deformation and the adhesion between the contact surfaces causes the increase in the friction coefficient and its variation.