Pratheek Shanthraj

Crystal plasticity study on stress and strain partitioning in a measured 3D dual phase steel microstructure

Dual phase steels are advanced high strength alloys typically used for structural parts and reinforcements in car bodies. Their good combination of strength and ductility and their lean composition render them an economically competitive option for realizing multiple lightweight design options in automotive engineering. The mechanical response of dual phase steels is the result of the strain and stress partitioning among the ferritic and martensitic phases and the individual crystallographic grains and subgrains of these phases. Therefore, understanding how these microstructural features influence the global and local mechanical properties is of utmost importance for the design of improved dual phase steel grades. While multiple corresponding simulation studies have been dedicated to the investigation of dual phase steel micromechanics, numerical tools and experiment techniques for characterizing and simulating real 3D microstructures of such complex materials have been emerged only recently. Here we present a crystal plasticity simulation study based on a 3D dual phase microstructure which is obtained by EBSD tomography, also referred to as 3D EBSD (EBSD—electron backscatter diffraction). In the present case we utilized a 3D EBSD serial sectioning approach based on mechanical polishing. Moreover, sections of the 3D microstructure are used as 2D models to study the effect of this simplification on the stress and strain distribution. The simulations are conducted using a phenomenological crystal plasticity model and a spectral method approach implemented in the Düsseldorf Advanced Material Simulation Kit (DAMASK).

A Flexible and Efficient Output File Format for Grain-Scale Multiphysics Simulations

Modern high-performing structural materials gain their excellent properties from the complex interactions of various constituent phases, grains, and subgrain structures that are present in their microstructure. To further understand and improve their properties, simulations need to take into account multiple aspects in addition to the composite nature. Crystal plasticity simulations incorporating additional physical effects such as heat generation and distribution, damage evolution, phase transformation, or changes in chemical composition enable the compilation of comprehensive structure–property relationships of such advanced materials under combined thermo-chemo-mechanical loading conditions. Capturing the corresponding thermo-chemo-mechanical response at the microstructure scale usually demands specifically adopted constitutive descriptions per phase. Furthermore, to bridge from the essential microstructure scale to the component scale, which is often of ultimate interest, a sophisticated (computational) homogenization scheme needs to be employed. A modular simulation toolbox that allows the problem-dependent use of various constitutive models and/or homogenization schemes in one concurrent simulation requires a flexible and adjustable file format to store the resulting heterogeneous data. Besides dealing with heterogeneous data, a file format suited for microstructure simulations needs to be able to deal with large (and growing) amounts of data as (i) the spatial resolution of routine simulations is ever increasing and (ii) more and more quantities are taken into account to characterize a material. To cope with such demands, a flexible and adjustable data layout based on HDF5 is proposed. The key feature of this data structure is the decoupling of spatial position and data, such that spatially variable information can be efficiently accommodated. For position-dependent operations, e.g., spatially resolved visualization, the spatial link is restored through explicit mappings between simulation results and their spatial position.

Correction to: A Flexible and Efficient Output File Format for Grain-Scale Multiphysics Simulations

The correct copyright line for this article is “The Author(s) 2017. This article is an open access publication”, rather than “The Minerals, Metals & Materials Society 2017” (as in the original HMTL version of the article).

FFT-based interface decohesion modelling by a nonlocal interphase

In this paper, two nonlocal approaches to incorporate interface damage in fast Fourier transform (FFT) based spectral methods are analysed. In FFT based methods, the discretisation is generally non-conforming to the interfaces and hence interface elements cannot be used. This limitation is remedied using the interfacial band concept, i.e., an interphase region of a finite thickness is used to capture the response of a physical sharp interface. Mesh dependency due to localisation in the softening interphase is avoided by applying established regularisation strategies, integral based nonlocal averaging or gradient based nonlocal damage, which render the interphase nonlocal. Application of these regularisation techniques within the interphase sub-domain in a one dimensional FFT framework is explored. The effectiveness of both approaches in terms of capturing the physical fracture energy, computational aspects and ease of implementation is evaluated. The integral model is found to give more regularised solutions and thus a better approximation of the fracture energy.