Browsing by Author "Andersson, Tom"
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Item Analysis of Discontinuities in Metallic Materials With the Extended Finite Element Method(2010) Andersson, Tom; Laukkanen, Anssi; Sovelletun mekaniikan laitos; Insinööritieteiden korkeakoulu; School of Engineering; Tuhkuri, JukkaThe goal of this work was to develop a finite element method code able to handle strong and weak discontinuities in two dimensional cases. The code is able to model crack (strong discontinuity) propagation and take into account the presence of precipitates. Precipitates (weak discontinuity) are modelled as small material domains with Young's modulus differing from the rest of the specimen. The code is written in Matlab utilizing the Getfem general purpose finite element (FE) library. Getfem-library is an open source library developed with C++. As case studies three edge crack configurations in a two dimensional tensile type fracture mechanics square specimen are considered. In these cases the specimen is loaded from its upper boundary and the lower boundary is fixed. In first case a stationary crack, with length of 3/10 the whole specimen is analyzed with the aim of verifying the code. In the eases to follow the crack propagation capabilities of the implementation are investigated. The initial crack length in these cases is 1/10 of the whole specimen. The maximum circumferential tensile stress criterion is used to calculate the crack propagation angle. In second case three different crack propagation variants are considered: one with loading perpendicular to the crack, one with loading parallel to the crack, and one with a 45° angle. The third case is similar to the first variant of case two only difference is that precipitates are included into the material. Constitutive properties of the precipitates differ in these analyses. The code was verified by crosschecking computed stress intensity factor values with the analytical ones. The computed results were in good agreement with the theory. The crack propagation was analyzed by comparing the computed crack growth angles and the ones given by the used crack growth criterion. The crack propagation and its behaviour near regions with discontinuously varying material properties were in good accordance with theoretical crack propagation. The Getfem-library is found to be effective and user friendly, regardless of the lack of documentation, in building XFEM codes. The code developed during this work will be used as a base for more sophisticated and effective XFEM codes.Item Crystal plasticity model for creep and relaxation deformation of OFP copper(Maney Publishing, 2024) Andersson, Tom; Lindroos, Matti; Pohja, Rami; Biswas, Abhishek; Nandy, Supriya; Pakarinen, Janne; Rantala, Juhani; Department of Mechanical Engineering; Materials to Products; VTT Technical Research Centre of Finland; Aalto UniversityWe demonstrate a dislocation density-based crystal plasticity (CP) model approach for simulating mesoscale deformation and damage. The existing CP framework is extended to be compatible with the oxygen-free phosphorous copper microstructure that is the focus of this study. The key aim is to introduce relevant plastic deformation mechanisms and to develop a failure model capable of depicting creep damage in the material. The effect of local variations in material is evaluated, and the model response is compared with experiments and characterisation. The basis of this work is CP material modelling, including grain orientation and size, obtained using electron backscatter diffraction and experimental test data of real relaxation test specimens. This will yield a realistic description of texture and grain shape and, ultimately, accurate stress–strain response at the microstructural level for further evaluation of performance with respect to material creep(−fatigue) damage.Item A multiscale modelling approach for estimating the effect of defects in unidirectional carbon fiber reinforced polymer composites(MDPI AG, 2019-06-12) Antin, Kim Niklas; Laukkanen, Anssi; Andersson, Tom; Smyl, Danny; Vilaça, Pedro; Department of Mechanical Engineering; VTT Technical Research Centre of FinlandA multiscale modelling approach was developed in order to estimate the effect of defects on the strength of unidirectional carbon fiber composites. The work encompasses a micromechanics approach, where the known reinforcement and matrix properties are experimentally verified and a 3D finite element model is meshed directly from micrographs. Boundary conditions for loading the micromechanical model are derived from macroscale finite element simulations of the component in question. Using a microscale model based on the actual microstructure, material parameters and load case allows realistic estimation of the effect of a defect. The modelling approach was tested with a unidirectional carbon fiber composite beam, from which the micromechanical model was created and experimentally validated. The effect of porosity was simulated using a resin-rich area in the microstructure and the results were compared to experimental work on samples containing pores.Item Process-Structure-Properties-Performance Modeling for Selective Laser Melting(Multidisciplinary Digital Publishing Institute (MDPI), 2019-11) Pinomaa, Tatu; Yashchuk, Ivan; Lindroos, Matti; Andersson, Tom; Provatas, Nikolas; Laukkanen, Anssi; Department of Computer Science; Professorship Vehtari Aki; VTT Technical Research Centre of Finland; McGill UniversitySelective laser melting (SLM) is a promising manufacturing technique where the part design, from performance and properties process control and alloying, can be accelerated with integrated computational materials engineering (ICME). This paper demonstrates a process-structure-properties-performance modeling framework for SLM. For powder-bed scale melt pool modeling, we present a diffuse-interface multiphase computational fluid dynamics model which couples Navier–Stokes, Cahn–Hilliard, and heat-transfer equations. A computationally efficient large-scale heat-transfer model is used to describe the temperature evolution in larger volumes. Phase field modeling is used to demonstrate how epitaxial growth of Ti-6-4 can be interrupted with inoculants to obtain an equiaxed polycrystalline structure. These structures are enriched with a synthetic lath martensite substructure, and their micromechanical response are investigated with a crystal plasticity model. The fatigue performance of these structures are analyzed, with spherical porelike defects and high-aspect-ratio cracklike defects incorporated, and a cycle-amplitude fatigue graph is produced to quantify the fatigue behavior of the structures. The simulated fatigue life presents trends consistent with the literature in terms of high cycle and low cycle fatigue, and the role of defects in dominating the respective performance of the produced SLM structures. The proposed ICME workflow emphasizes the possibilities arising from the vast design space exploitable with respect to manufacturing systems, powders, respective alloy chemistries, and microstructures. By digitalizing the whole workflow and enabling a thorough and detailed virtual evaluation of the causal relationships, the promise of product-targeted materials and solutions for metal additive manufacturing becomes closer to practical engineering application.