Hansun Ryou

Incorporation of sheet-forming effects in crash simulations using ideal forming theory and hybrid membrane and shell method

In order to achieve reliable but cost-effective crash simulations of stamped parts, sheet-forming process effects were incorporated in simulations using the ideal forming theory mixed with the three-dimensional hybrid membrane and shell method, while the subsequent crash simulations were carried out using a dynamic explicit finite element code. Example solutions performed for forming and crash simulations of I- and S-shaped rails verified that the proposed approach is cost effective without sacrificing accuracy. The method required a significantly small amount of additional computation time, less than 3% for the specific examples, to incorporate sheet-forming effects into crash simulations. As for the constitutive equation, the combined isotropic-kinematic hardening law and the nonquadratic anisotropic yield stress potential as well as its conjugate strain-rate potential were used to describe the anisotropy of AA6111-T4 aluminum alloy sheets.

Crash Simulations Considering Sheet Forming Effects Based on Ideal Forming Theory and Hybrid Membrane/Shell Method

In order to achieve reliable but cost‐effective crash simulations of stamped parts, sheet forming process effects were incorporated in simulations using the ideal forming theory mixed with the 3D hybrid membrane/shell method, while the subsequent crash simulations were carried out using a dynamic explicit finite element code. Example solutions performed for forming and crash simulations of I‐ and S‐shaped rails verified that the proposed approach is cost‐effective without sacrificing accuracy. The method required a significantly small amount of additional computation time, less than 3% for the specific examples, to incorporate sheet forming effects to crash simulations. As for the constitutive equation, the combined isotropic‐kinematic hardening law and the non‐quadratic anisotropic yield stress potential as well as its conjugate strain‐rate potential were used to describe the anisotropy of AA6111‐T4 aluminum alloy sheets.

Impact Analysis of Fiber-reinforced Composites Based on Elasto-plastic Constitutive Law

Impact analysis of 3D braided composites and laminated plane woven fabric composites was performed using the elasto-plastic constitutive law to describe the nonlinear, anisotropic and asymmetric properties of fiber-reinforced composites. As for the yield criterion, the modified Drucker—Prager yield criterion was utilized to represent the anisotropic and asymmetric properties, while the anisotropic hardening was described based on the kinematic hardening with the anisotropic evolution of the back-stress. Experiments to obtain the material parameters of the proposed constitutive law were also carried out based on uni-axial tension and compression tests for fiber-reinforced composites. Then, the proposed constitutive law was implemented into a finite element code and was verified by comparing the finite element simulation of the impact tests with experiments. In addition, impact performance of the braided composites and laminated composites was also compared with each other.

Numerical implementation of modified Coulomb-Mohr yield criterion for anisotropic and asymmetric materials

Development and numerical implementation for an elastoplastic constitutive model for anisotropic and asymmetric materials are presented in this paper. The Coulomb-Mohr yield criterion was modified to consider both the anisotropic and asymmetric properties. The modified yield criterion is an isotropic function of the principal values of a symmetric matrix which is linearly transformed from the Cauchy stress space. In addition to the constitutive equation, the numerical treatment for the singularity in the vertex region of yield surface and stress integration algorithm based on elastoplasticity were presented. In order to assess the accuracy of numerical algorithm, isoerror maps were considered. Also, extension of a strip with a circular hole was simulated and results compared with those obtained using the (smooth) Mises yield criterion to validate stress output for a complex stress state.

Elasto-plastic analysis of the impact performance of woven fabric composites

The impact performance of laminated plain-woven fabric composites was analysed here using the elasto-plastic constitutive law, which can account for the anisotropic and asymmetric properties of fibre-reinforced plastics. The isotropic yield criterion was modified to account for the anisotropic and asymmetric initial yielding, while the kinematic hardening law with anisotropic evolution of back-stress was used for the anisotropic hardening behaviour. The impact tests were performed on laminated plain-woven composites. The simulation results for the impact tests compared well with experimental results.