Papers by Keyword: Constitutive Modeling

Abstract: High Mn steels demonstrate an exceptional combination of high strength and ductility due to their high work hardening rate during deformation. The microstructure evolution and work hardening behavior of Fe18Mn0.6C1.5Al TWIP steel in uni-axial tension were examined. The purpose of this study was to determine the contribution of all the relevant deformation mechanism : slip, twinning and dynamic strain aging. Constitutive modeling was carried out based on the Kubin-Estrin model, in which the densities of mobile and forest dislocations are coupled in order to account for the continuous immobilization of mobile dislocations during straining. These coupled dislocation densities were also used for simulating the contribution of dynamic strain aging on the flow stress. The model was modified to include the effect of twinning.

Abstract: In order to simulate manufacturing processes, it is essential to have accurate information about mechanical behaviour of material for different deformation conditions depending on the type of the process. In finite element (FE) analysis based techniques for simulation, a constitutive equation is needed to model the mechanical behaviour of material. In the case of metal cutting, the Johnson and Cook (JC) flow stress model is the most suitable constitutive equation to be used in simulation since it contains the effects of strain, strain-rate and temperature. It is needed to evaluate the parameters and constants of the JC model to make it applicable in FE simulations. There are several ways to evaluate the parameters of the equation: experimental such as high strain-rate compression tests called “Split Hopkinson Pressure Bar” which is relatively complicated and expensive technique requiring special testing apparatus; and analytical approach based on Oxley’s theory. An integral method containing quasi-static compression and machining tests have been used in this paper to evaluate the JC equation parameters by fitting data from both tests for a Ti-alloy (Ti6Al4V). Finally the estimated JC model is validated by some other machining tests.

Abstract: A dynamic, nonlinear model for magnetic induction and strain response of cubic magnetostrictive materials to 3-D dynamic magnetic fields and 3-D stresses is developed. Dynamic eddy current losses and inertial stresses are modeled by coupling Maxwell’s equations to Newton’s second law through a nonlinear constitutive model. The constitutive model is derived from continuum thermodynamics.

Abstract: Experiments have shown that the localization of transformation in NiTi shape memory alloys (SMAs) is an important factor in determining their mechanical response during cyclic loading. A one-dimensional constitutive model for the cyclic behavior of SMAs is presented that takes into account the localization of transformation and transformation-induced plasticity. An internal variable is introduced that characterizes the amount of temperature-dependent cyclic change. The results of simulations at two different temperatures are also presented.

Abstract: In order to understand the grain size and porosity dependent mechanical behavior of porous, multi-phase nanocrystalline ceramics, each phase is treated as a mixture of grain interior and grain boundary, and pores are taken as a single phase. In conjunction with the secant-modulus approach and iso-strain assumption, Budiansky’s self-consistent method is extended to build a constitutive model for nanocrystalline ceramics with small plastic deformation. Based on the developed model, the predicted yield strength (σ0.2) values of porous, multi-phase nanocrystalline ceramics with different grain size and porosity are compared with experimental data in the literature, the comparison shows that the predictions are in good agreement with the published data. This suggests that the developed model is capable of describing the grain size and porosity dependent mechanical behaviors of nanocrystalline ceramics with small plastic deformation.

Abstract: This paper discusses ratchetting deformation of lead-free solder Sn/3Ag/0.5Cu and lead-containing solder alloy Sn/37Pb with several stress amplitudes and stress ratios of the maximum stress to the minimum stress. First the uniaxial ratchetting tests
are conducted with three maximum stresses and five stress ratios. The all tests are conducted using cylindrical bulk specimens of the solder alloys at 313 K. The test results show that there is the difference in the viscoplastic deformation behavior between two solder alloys. The relationship between ratchetting strain and time is estimated by Biley-Norton law to explain that the uniaxial ratchetting deformation is strongly dominated by the viscous deformation. Finally, the ratchetting deformation is simulated by the dislocation based constitutive model proposed by Estrin [1]. The simulations show that there is a possibility to simulate the uniaxial ratchetting by clarifying the dislocation mechanism of the solder alloys.

Abstract: The objective of this paper is to extend the capability of analyzing the time dependence and coupling of temperature, stress and strain effects on the macroscopic and microscopic structures subjected to quenching, and to introduce a theory of the kinetic of the phase transformation. Strain due to phase transformation, transformation plasticity and thermal expansion are the dominant factors that need to be included in the simulation of a quenching process. The evolution of the microstructure also influences the constitutive equations. In particular, as the temperature changes from the high to phase transformation, temperature and then room temperature, the stress-strain relationship changes from elastic-plastic strain. Therefore, in order to obtain a high strength and ductility in carbon steels, transformation plasticity often has a major effect in increasing of the residual stress during quenching process. In this paper, we measured temperature change and distortion occurring during the quenching process of a carbon steel(SCr420) by thermal simulation machine (Gleeble 1500) are used to determine the parameter of transformation plasticity due to the generation of martensite. The modeling of martensitic transformation plasticity is also verified by using of computational simulation of the quenching process.