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Deformation Mechanism in Single Point Incremental Forming (SPIF) and Significance of Crystallographic Texture in Sheet Metal Forming Operations
Published in Kakandikar Ganesh Marotrao, Anupam Agrawal, D. Ravi Kumar, Metal Forming Processes, 2023
During plastic deformation, polycrystalline materials possess anisotropic behavior due to heterogeneous tendency of crystallographic microstructure (Dwivedi 2016; Kumar 2016). Recently, a few numerical studies were carried out considering the microstructure and texture evolution of polycrystalline material during the plastic deformation by Crystal Plasticity Finite Element (CPFE) model. The method is capable to predict formability in polycrystalline material by involving the fundamental mechanism of dislocation movements and crystallographic slip systems. Farukh et al. (2016) had developed physically-based crystal plasticity models to predict the behavior of individual grains in polycrystalline materials. In addition, crystal plasticity when combined with finite element method is capable of predicting the global and local stresses, and strain response of crystalline materials subjected to different kinds of loading Conditions. To predict the material response at microstructural level, Farukh et al. (2016) utilized representative volume element (RVE) including adequate quantity of grains. The technique was capable to predict the global behavior by employing real microstructural arrangement in comparison to virtual microstructures created by Voronoi tessellation technique. The overall technique is shown in Figure 6.17 which includes a basic step to procure real microstructures from scanning electron microscope and to determine the coordinates of the grain boundaries by using image-processing code developed within MATLAB. The generated geometry through the calculated coordinates was utilized as an input to ABAQUS CAE software which in conjugation to FE model generated the realistic grain microstructure. A flow chart depicting the procedure to produce RVE is shown in Figure 6.18. The model is grounded on two dimensional (surface) images of the material and thus, neglects the material behavior in the third dimension.
Modelling and simulation of dynamic recrystallisation based on multi-phase-field and dislocation-based crystal plasticity models
Published in Philosophical Magazine, 2020
In recent years, numerical simulations of DRX have been conducted using methods such as the cellular automaton [4], level-set [5,6], and phase-field methods [7,8]. A phase-field model expresses the phase transformation using order parameters, which are continuous functions. It is widely used for microstructure formation because it does not require special handling of the interface. A multi-phase-field (MPF) model [9] is an especially useful phase-field model because it expresses each grain by its own order parameter and can thus distinguish between grains clearly. However, there are no DRX models that describe the order field and deformation field simultaneously. The deformation field should be described in terms of crystal plasticity because crystal deformation and the associated accumulation of dislocations should be taken into account.
Micromechanical modelling of coupled crystal plasticity and hydrogen diffusion
Published in Philosophical Magazine, 2019
Hamad ul Hassan, Kishan Govind, Alexander Hartmaier
In order to model these mechanisms that have been proposed in the literature, we need to solve the hydrogen diffusion equation to determine how the hydrogen is distributed inside the material and to couple this with the micromechanical constitutive response of the material. Crystal plasticity is more predictive and robust than macroscopic plasticity since it explicitly addresses the evolution of crystallographic textures and models both anisotropic elasticity and plasticity. It also considers the stress–strain response to be dependent on the orientations of the grains. In this paper, we will highlight the importance of using a crystal plasticity model at the microstructural level to study the interaction of hydrogen with metals. Specifically, the redistribution of hydrogen in a precharged microstructure under the influence of a biaxial strain will be studied. Furthermore, the influence of prestraining (to replicate the internal stresses due to heat treatment etc.) on the hydrogen diffusion will be analysed and compared with the simultaneous loading case to understand the transient behaviour of hydrogen. Permeation tests will also be performed to observe the influence of trapping effect of dislocations on the effective diffusivity through the application of prestrains and by the variation of trap binding energy. Metals may contain all kinds of hydrogen traps, but in this work, we restrict ourselves only to dislocation trapping sites and their evolution with plastic deformation. The coupled crystal plasticity and hydrogen diffusion model is discussed in the following section, where, at first, the crystal plasticity formulation is given followed by the hydrogen transport model. It is then followed by the description of our results and their discussion where the developed model is applied to different loading cases to characterise the influence of trapping by dislocations on the effective diffusivity. The results of the coupled model, the impact on diffusion localisation and the further capabilities of this model are finally summarised.