Forming limit diagrams (FLDs) are calculated based on both the Marciniak and Kuczynski (M-K) model and the analysis proposed by Jones and Gillis (J-G). J-G analysis consisted of plastic deformation approximation by three deformation phases. These phases consisted of homogeneous deformation up to the maximum load (Phase I), deformation localization under constant load (phase II) and local necking with a precipitous drop in load (phase III). In the present study, case I and case II of Hill’s non-quadratic yield function were used for the first time. It is assumed that sheets obey the power-law flow rule and in-plane isotropy is satisfied. Calculated FLDs from this analysis are compared with the experimental data of aluminum alloys 3003-O, 2036-T4 and AK steel reported by other references. Calculated FLDs showed that limit strain predictions based on case I and case II of the Hill’s non-quadratic yield function are fairly well correlated to experiments when J-G model is used. تفاصيل المقالة

In the present study, plasticity induced crack closure (PICC) concept and three dimensional (3D) finite element methods (FEM) are used to study the effect of compressive residual stress field on the fatigue crack growth from a hole. To investigate the effect of compressive residual stress on crack opening levels and crack shape evolution, Carlson’s experiments were simulated. Crack shape evolution is investigated by employing an automatic remeshing technique using MATLAB-ABAQUS code. The effect of mesh element size is considered by using element sizes of 0.025mm and 0.0125mm. Crack opening level results indicate that the applied residual stress increases the opening levels with an average of 45%. The higher opening levels results in higher number of fatigue cycles by a ratio of 3.07 for 1.9mm surface crack growth increment. Comparing the result obtained with Carlson’s experiments indicates that the crack closure method employed in the present analysis is in good agreement. Comparing the results with Jones’ supeposition method, moreover, illustrates that present paper method is more accurate. تفاصيل المقالة

The behavior of an exponentially graded hybrid cylindrical shell subjected to an axisymmetric thermo-electro-mechanical loading placed in a constant magnetic field is investigated. The hybrid shell is consisted of a functionally graded host layer embedded with pyroelectric layers as sensor and/or actuator that can be imperfectly bonded to the inner and the outer surfaces of a shell. The shell is simply supported and could be rested on an elastic foundation. The material properties of the host layer are assumed to be exponentially graded in the radial direction. To solve governing differential equations, the Fourier series expansion method along the longitudinal direction and the differential quadrature method (DQM) across the thickness direction are used. Numerical examples are presented to discuss effective parameters influence on the response of the hybrid shell. تفاصيل المقالة

Semi-solid materials undergo strain localization and shear band formation as a result of granular nature of semi-solid deformation. In the present study, to analyze the shear localization, a unified viscoplastic constitutive model was developed for the homogeneous flow. Then, a linearized analysis of the stability performed by examining the necessary condition for the perturbation growth. For this purpose, a shear layer model was considered to analyze the perturbation growth and subsequent instability. The perturbation analysis revealed that the failure mode in semi-solid materials is diffused with long wave length regime, rather than to be localized and exhibiting short wave length regime. Moreover, decreasing the solid skeleton has a retarding effect on the perturbation growth and localization at low and modest strain rates. The performed analysis showed that the localization analysis results in a new interpretation for the micro-mechanisms of the semi-solid deformation. The constitutive model was fairly well correlated with the experimental results. تفاصيل المقالة