Papers by Keyword: Constitutive Modeling

Abstract: In order to improve the understanding deformation behaviors of thermal compressive of ZK30 magnesium alloy, carried out a series of thermal compressive tests with height reduction 60% of specimens were performed at deformation temperature range of 523-673 K, and strain rates range of 0.001-1 s⁻¹ on Gleeble-1500 thermo-mechanical simulator. Based on an Arrhenius-type equation constructs a nonlinear flow model and its constitutive equation, are employed to study the deformation behavior and the relationship between deformation temperature, strain rate and flow stress. For higher deformation temperature and lower strain rate, the true stress-strain curves show a characteristic of dynamic recrystallization. With the increase of deformation temperature and the decrease of strain rate the flow stress decreases, also the dynamic recrystallization becomes easier.

Abstract: Advanced light metals have recently attracted the interest of the aerospace and automotive industry. The need for accurate description of their cyclic inelastic response under various loading histories becomes increasingly important. Cyclic mean stress relaxation and ratcheting are two of the phenomena under investigation. A combined kinematic isotropic hardening model is implemented for the simulation of the behavior of Aluminum and Titanium alloys in uniaxial mean stress relaxation and ratcheting. The obtained results indicate that the model can perform well in these cases. This preliminary analysis provides useful insight for the evaluation of the models capabilities.

Abstract: Sheet metals exhibit anisotropic plastic behavior due to the large plastic deformations that occur during the rolling of the sheet and which induce texture and are responsible for the initial anisotropy. There exist various possibilities to introduce plastic anisotropy into the finite element modelling of sheet metal forming. The initial yield anisotropy can be incorporated either through an anisotropic yield surface or directly by means of a crystallographic texture model. Here, one basically differentiates between empirical and phenomenological anisotropic yield function equations, where the anisotropy coefficients can be obtained from mechanical tests, and texture-based models the coefficients of which are directly determined based on experimentally obtained orientation distributions. Another type of anisotropy that can be usually found in anisotropic materials is the elastic anisotropy. In metal plasticity one often considers the effect of elastic anisotropy significantly smaller than the effect of plastic anisotropy. Consequently, elastic isotropic expressions are often used for elastic stored energy functions with anisotropic yield criteria. However, the influence of elastic anisotropy in the elastoplastic behavior can be very important especially during elastic recovery processes during unloading after forming and springback. This research focuses, therefore, on the study of the influence of elastic anisotropy on the amount of springback in bending processes such as e.g. unconstrained bending. We discuss a finite strain material model for evolving elastic and plastic anisotropy combining nonlinear isotropic and kinematic hardening. The evolution of elastic anisotropy is described by representing the Helmholtz free energy as a function of a family of evolving structure tensors. In addition, plastic anisotropy is modelled via the dependence of the yield surface on the same family of structure tensors. Exploiting the dissipation inequality leads to the interesting result that all tensor-valued internal variables are symmetric. Thus, the integration of the evolution equations can be efficiently performed by means of an algorithm that automatically retains the symmetry of the internal variables in every time step. The material model has been implemented as a user material subroutine UMAT into the commercial finite element software ABAQUS/Standard and has been applied to the simulation of springback of unconstrained bending.

Abstract: This lecture presents constitutive modeling of the homogenized elastic-viscoplastic behavior of pore-pressurized anisotropic open-porous bodies. The base solids are assumed to be metallic materials at small strains and rotations. First, by describing micro-macro relations relevant to periodic unit cells of anisotropic open-porous bodies with pore pressure, constitutive features are discussed for the viscoplastic macrostrain rate in steady states. Second, on the basis of the constitutive features found, the viscoplastic macrostrain rate is represented as an anisotropic function of Terzaghi’s effective stress. Third, the resulting viscoplastic equation is used to simulate the homogenized elastic-viscoplastic behavior of an ultrafine plate-fin structure and a thick perforated plate subjected to macroscopic loading in the absence and presence of pore pressure. The corresponding FE homogenization analysis is performed for comparison to validate the developed viscoplastic equation.

Abstract: In order to obtained the constitutive equations of thermal insulation masonry, the four masonry with different angles has pressed. Study on thermal insulation of masonry compressive mechanical parameters of constitutive equation and two-stage by compression stress-strain curves obtained in the servo press machine tests and data processing. The Basic mechanics parameters can be provided for finite element analysis of thermal insulation composite wall. The experiments showed that the constitutive model is discretization and the maximum stress and strain by press machine testing is different from brick masonry. The constitutive model is close with curve by press machine testing. The performance of mechanics in thermal insulation wall can be application by the stress-strain curves of thermal insulation of masonry. The stress-strain curves based experiments can be used finite element analysis of thermal insulation wall.

Abstract: Hyperelastic material simulation is necessary for proper testing of products functionality in cases where prototype testing is expensive or not possible. Hyperelastic material is nonlinear and more than one stress-strain response of the material is required for its characterization. The study was focused on prediction of hyperelastic behavior of rubber neglecting the viscoelastic and creep effects in rubber. To obtain the stress strain response of rubber, uniaxial and biaxial tension tests were performed. The data obtained from these tests was utilized to find the coefficients of Mooney-Rivlin, Odgen and Arruda Boyce models. Verification of the behavior as predicted by the fitted models was carried out by comparing the experimental data of a planar shear test with its simulation using the same constitutive models.

Abstract: Two non-quadratic orthotropic yield functions called Yld2011-18p (containing 18 param-eters) and Yld2011-27p (containing 27 parameters) are proposed. The formulations are based on theestablished concept of linear transformations operating on the stress deviator. Application examplesreveal the capabilities of both yield functions to accurately describe complex plastic anisotropy ofsheet metals.

Abstract: Constitutive modeling in unsaturated soil is always a big challenge in Geo-technique problems. Since Alonso et al suggested the Basic Barcelona Model (BBM) in 1990. Many researchers contribute works on constitutive models in last two decades. The SFG model presented by Sheng, Fredlund and Gens describes the mechanical and hydraulic behaviors of an unsaturated soil accurately. It is currently considered the most reasonable model for unsaturated soil. In this paper, the authors attempts to prove the volume change behavior in SFG model by two basic unsaturated soil experiments in testing two different soils. The experimental data and the fitting processes are provided.

Abstract: An apparatus to measure compressive creep in carbon cathode materials has been developed. Short-time creep were measured at 30°C，965°C and during aluminum electrolysis at 965°C. The creep strain increases with stress, indicating that the creep behavior is of the stress dependency. The ranking from low to high creep was at 30°C<965°C

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