Authors: Yuung Hwa Lu, Fung Huei Yeh, Ching Lun Li
Abstract: This paper combines Feasible Sequential Quadratic Programming (FSQP) and
elasto-plastic finite element method to perform the inverse estimation of the material constitutive constants and friction coefficient in the nosing process. The aim is to improve the accuracy of constitutive constants and working parameters in the classical analysis based on the material flow homogeneity or trial and error. In the prediction of the friction coefficient at the interface between metal and tool surface, the simulated load, calculated from the optimal material constants, shows
good coincidence with the experimental load when the optimal friction coefficient is reached. The investigation of these inverse models identify that the combination of FSQP and elasto-plastic finite element method can supply a useful optimal approach in the industrial application.
685
Authors: G.H. Majzoobi, S. Faraj Zadeh Khosroshahi, H. Beik Mohammadloo
Abstract: Identification of the constants of material models is always a concern. In the present work, a combined experimental, numerical and optimization technique is employed to determine the constants of Zerilli-Armstrong model. The experiments are conducted on a compressive Hopkinson bar, the simulations are performed using finite element method and optimization is carried out using genetic algorithm. In the method adopted here, there is no need for experimental stress-strain curve which is always accompanied by restricting phenomenon such as necking in tension and bulging in compression. Instead of stress-strain curve, the difference between the post-deformation profiles of specimens obtained from experiment and the numerical simulations is adopted as the objective function for optimization purposes. The results suggest that the approach introduced in this work can substitute costly instrumentations normally needed for obtaining stress-strain curves at high strain rates and elevated temperature.
862
Abstract: This paper introduces a fast and accurate procedure for determining the constants of magnesium AZ31 alloy at 713 K. The material behaviour is modelled by means of the power law relationship between the equivalent flow stress, the equivalent strain and the equivalent strain-rate within a narrow equivalent strain-rate range. Bulging tests were carried out in isothermal conditions (713 K) and at constant pressure in order to determine the material constants. It is necessary to evaluate the displacement and the thickness evolutions at the dome apex of the metal sheet. The time-displacement curve was obtained by laser measurements whereas a large number of bulging tests, interrupted at preset time intervals, were carried out to evaluate the thickness. The thickness was measured directly using a two-digit micrometer. The material constants, m, n and K were obtained in the power law relationship by means of constant pressure bulging tests coupled with the use of an inverse analysis technique. The results of comparison between experimental and numerical tests are shown and they indicate that the material constants can be accurately evaluated.
643
Authors: Xin Zhao, Hong Zhao, Rui Zhang
Abstract: The hot deformation behavior of TC18 titanium alloy was studied in alpha-beta phase region. The temperature range was 1023-1123K and strain rate range 1-0.001-1s-1. The material constants of the alloy, including deformation activation energy ΔH as 364.823kJ / mol, stress-level coefficient α as 0.0086mm2/ N, stress exponential n as 3.8442 and structural factor A as 1.2601×1015s–1 were derived by Zener-Hollomon method from the interdependencies of flow stress, strain rate and temperature
3323
Authors: Xiao Jun Zuo, Jun Chu Li, Da Hai Liu, Long Fei Zeng
Abstract: Constructing accurate constitutive equation from the optimal material constants is the basis for finite element numerical simulation. To accurately describe the creep ageing behavior of 2A12 aluminum alloy, the present work is tentatively to construct an elastic-plastic constitutive model for simulation based on the ANSYS environment. A time hardening model including two stages of primary and steady-state is physically derived firstly, and then determined by electronic creep tensile tests. The material constants within the creep constitutive equations are obtained. Furthermore, to verify the feasibility of the material model, the ANSYS based numerical scheme is established to simulate the creep tensile process by using the proposed material model. Results show that the creep constitutive equation can better describe the deformation characteristics of materials, and the numerical simulations and experimental test points are in good agreement.
1497
