S. D. Akbarov^1,2, S. Karakaya³

CMC-Computers, Materials & Continua, Vol.22, No.1, pp. 1-38, 2011, DOI:10.3970/cmc.2011.022.001

Abstract The 3D approach was employed for investigations of the stability loss of the solid circular cylinder made from viscoelastic composite material. This approach is based on investigations of the evolution of the initial infinitesimal imperfections of the cylinder within the scope of 3D geometrically nonlinear field equations of the theory of viscoelasticity for anisotropic bodies. The numerical results of the critical forces and critical time are presented and discussed. To illustrate the importance of the results obtained using the 3D approach, these results are compared with the corresponding ones obtained by employing various approximate beam theories. The viscoelasticity properties of… More >

CMC-Computers, Materials & Continua, Vol.18, No.3, pp. 271-300, 2010, DOI:10.3970/cmc.2010.018.271

Abstract The processing maps are a superimposition of iso-efficiency contour map and flow instability map, which are used to design hot working processing conditions in a wide variety of materials. In order to construct the processing maps, the efficiency of power dissipation and an instability criterion taking into account the contribution of strain and microstructure evolution are proposed based on a set of microstructure-based viscoplastic constitutive equations. In viscoplastic constitutive equations, the grain size of matrix phase and the dislocation density are taken as internal state variables. And, the material constants in present equations can be identified by a genetic algorithm… More >

Hieu H. Pham¹, Tahir Ça ˇgın¹

CMC-Computers, Materials & Continua, Vol.16, No.2, pp. 175-194, 2010, DOI:10.3970/cmc.2010.016.175

Abstract We analyze the lattice dynamics of Fe in different crystal phases (bcc, fcc and hcp) by using density-functional theory. The study on equations of states indicates that bcc Fe is more stable than fcc and hcp Fe at low pressures. However, dynamical instabilities in lattice vibrations of bcc Fe predict a phase transformation from bcc to hcp at higher pressures. We reported a complete set of second-order and third-order elastic constants of Fe in these three phases. We observed a linear variation in the values of second order elastic constant as a function of increased pressures. The phonon spectra were… More >