| 1. |
- Amouzgar, Kaveh
(author)
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Metamodel based multi-objective optimization
- 2015
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Licentiate thesis (other academic/artistic)abstract
- As a result of the increase in accessibility of computational resources and the increase in the power of the computers during the last two decades, designers are able to create computer models to simulate the behavior of a complex products. To address global competitiveness, companies are forced to optimize their designs and products. Optimizing the design needs several runs of computationally expensive simulation models. Therefore, using metamodels as an efficient and sufficiently accurate approximate of the simulation model is necessary. Radial basis functions (RBF) is one of the several metamodeling methods that can be found in the literature.The established approach is to add a bias to RBF in order to obtain a robust performance. The a posteriori bias is considered to be unknown at the beginning and it is defined by imposing extra orthogonality constraints. In this thesis, a new approach in constructing RBF with the bias to be set a priori by using the normal equation is proposed. The performance of the suggested approach is compared to the classic RBF with a posteriori bias. Another comprehensive comparison study by including several modeling criteria, such as problem dimension, sampling technique and size of samples is conducted. The studies demonstrate that the suggested approach with a priori bias is in general as good as the performance of RBF with a posteriori bias. Using the a priori RBF, it is clear that the global response is modeled with the bias and that the details are captured with radial basis functions.Multi-objective optimization and the approaches used in solving such problems are briefly described in this thesis. One of the methods that proved to be efficient in solving multi-objective optimization problems (MOOP) is the strength Pareto evolutionary algorithm (SPEA2). Multi-objective optimization of a disc brake system of a heavy truck by using SPEA2 and RBF with a priori bias is performed. As a result, the possibility to reduce the weight of the system without extensive compromise in other objectives is found.Multi-objective optimization of material model parameters of an adhesive layer with the aim of improving the results of a previous study is implemented. The result of the original study is improved and a clear insight into the nature of the problem is revealed.
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| 2. |
- Amouzgar, Kaveh, 1980-
(author)
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Metamodel Based Multi-Objective Optimization with Finite-Element Applications
- 2018
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Doctoral thesis (other academic/artistic)abstract
- As a result of the increase in accessibility of computational resources and the increase of computer power during the last two decades, designers are able to create computer models to simulate the behavior of complex products. To address global competitiveness, companies are forced to optimize the design of their products and production processes. Optimizing the design and production very often need several runs of computationally expensive simulation models. Therefore, integrating metamodels, as an efficient and sufficiently accurate approximate of the simulation model, with optimization algorithms is necessary. Furthermore, in most of engineering problems, more than one objective function has to be optimized, leading to multi-objective optimization(MOO). However, the urge to employ metamodels in MOO, i.e., metamodel based MOO (MB-MOO), is more substantial.Radial basis functions (RBF) is one of the most popular metamodeling methods. In this thesis, a new approach to constructing RBF with the bias to beset a priori by using the normal equation is proposed. The performance of the suggested approach is compared to the classic RBF and four other well-known metamodeling methods, in terms of accuracy, efficiency and, most importantly, suitability for integration with MOO evolutionary algorithms. It has been found that the proposed approach is accurate in most of the test functions, and it was the fastest compared to other methods. Additionally, the new approach is the most suitable method for MB-MOO, when integrated with evolutionary algorithms. The proposed approach is integrated with the strength Pareto evolutionary algorithm (SPEA2) and applied to two real-world engineering problems: MB-MOO of the disk brake system of a heavy truck, and the metal cutting process in a turning operation. Thereafter, the Pareto-optimal fronts are obtained and the results are presented. The MB-MOO in both case studies has been found to be an efficient and effective method. To validate the results of the latter MB-MOO case study, a framework for automated finite element (FE) simulation based MOO (SB-MOO) of machining processes is developed and presented by applying it to the same metal cutting process in a turning operation. It has been proved that the framework is effective in achieving the MOO of machining processes based on actual FE simulations.
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| 3. |
- Amouzgar, Kaveh, 1980-, et al.
(author)
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Multi-objective optimization of material model parameters of an adhesive layer by using SPEA2
- 2015
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In: Advances in structural and multidisciplinary optimization. - : The International Society for Structural and Multidisciplinary Optimization (ISSMO). - 9780646943947 ; , s. 249-254
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Conference paper (peer-reviewed)abstract
- The usage of multi material structures in industry, especially in the automotive industry are increasing. To overcome the difficulties in joining these structures, adhesives have several benefits over traditional joining methods. Therefore, accurate simulations of the entire process of fracture including the adhesive layer is crucial. In this paper, material parameters of a previously developed meso mechanical finite element (FE) model of a thin adhesive layer are optimized using the Strength Pareto Evolutionary Algorithm (SPEA2). Objective functions are defined as the error between experimental data and simulation data. The experimental data is provided by previously performed experiments where an adhesive layer was loaded in monotonically increasing peel and shear. Two objective functions are dependent on 9 model parameters (decision variables) in total and are evaluated by running two FEsimulations, one is loading the adhesive layer in peel and the other in shear. The original study converted the two objective functions into one function that resulted in one optimal solution. In this study, however, a Pareto frontis obtained by employing the SPEA2 algorithm. Thus, more insight into the material model, objective functions, optimal solutions and decision space is acquired using the Pareto front. We compare the results and show good agreement with the experimental data.
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| 4. |
- Andersson, Tobias, et al.
(author)
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Meso-Mechanical Modelling Of Thin Adhesive Layers
- 2004
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In: ECF15, Stockolm 2004.
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Conference paper (other academic/artistic)abstract
- A meso-mechanical finite element model for a thin adhesive layer is developed. The model is calibrated to experimental results where the adhesive layer is loaded in monotonically increasing peel or shear, cf. Andersson and Stigh [1] and Alfredsson et al. [2], and to an in situ SEM study of the fracture process. The purpose of the meso-mechanical finite element model is to facilitate the development of constitutive laws for adhesive layers. Ideas developed by Needleman [3], where structural continuum elements are bonded by cohesive elements are used as a basis for the finite element mesh. This thus enables micro cracks to propagate along the finite element boundaries. The simulations are found to be in good agreement with the experiments. The model is also capable of reproducing realistically the deformation observed in both peel [1] and shear [2] experiments.
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| 5. |
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| 6. |
- Arjomandi Rad, Mohammad, et al.
(author)
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Correlation-based feature extraction from computer-aided design, case study on curtain airbags design
- 2022
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In: Computers in industry (Print). - : Elsevier. - 0166-3615 .- 1872-6194. ; 138
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Journal article (peer-reviewed)abstract
- Many high-level technical products are associated with changing requirements, drastic design changes, lack of design information, and uncertainties in input variables which makes their design process iterative and simulation-driven. Regression models have been proven to be useful tools during design, altering the resource-intensive finite element simulation models. However, building regression models from computer-aided design (CAD) parameters is associated with challenges such as dealing with too many parameters and their low or coupled impact on studied outputs which ultimately requires a large training dataset. As a solution, extraction of hidden features from CAD is presented on the application of volume simulation of curtain airbags concerning geometric changes in design loops. After creating a prototype that covers all aspects of a real curtain airbag, its CAD parameters have been analyzed to find out the correlation between design parameters and volume as output. Next, using the design of the experiment latin hypercube sampling method, 100 design samples are generated and the corresponding volume for each design sample was assessed. It was shown that selected CAD parameters are not highly correlated with the volume which consequently lowers the accuracy of prediction models. Various geometric entities, such as the medial axis, are used to extract several hidden features (referred to as sleeping parameters). The correlation of the new features and their performance and precision through two regression analyses are studied. The result shows that choosing sleeping parameters as input reduces dimensionality and the need to use advanced regression algorithms, allowing designers to have more accurate predictions (in this case approximately 95%) with a reasonable number of samples. Furthermore, it was concluded that using sleeping parameters in regression-based tools creates real-time prediction ability in the early development stage of the design process which could contribute to lower development lead time by eliminating design iterations.
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| 7. |
- Arjomandi Rad, Mohammad, 1987, et al.
(author)
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Image regression-based digital qualification for simulation-driven design processes, case study on curtain airbag
- 2023
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In: Journal of engineering design (Print). - : Taylor & Francis. - 0954-4828 .- 1466-1837. ; 34:1, s. 1-22
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Journal article (peer-reviewed)abstract
- Today digital qualification tools are part of many design processes that make them dependent on long and expensive simulations, leading to limited ability in exploring design alternatives. Conventional surrogate modelling techniques depend on the parametric models and come short in addressing radical design changes. Existing data-driven models lack the ability in dealing with the geometrical complexities. Thus, to address the resulting long development lead time problem in the product development processes and to enable parameter-independent surrogate modelling, this paper proposes a method to use images as input for design evaluation. Using a case study on the curtain airbag design process, a database consisting of 60,000 configurations has been created and labelled using a method based on dynamic relaxation instead of finite element methods. The database is made available online for research benchmark purposes. A convolutional neural network with multiple layers is employed to map the input images to the simulation output. It was concluded that the showcased data-driven method could reduce digital testing and qualification time significantly and contribute to real-time analysis in product development. Designers can utilise images of geometrical information to build real-time prediction models with acceptable accuracy in the early conceptual phases for design space exploration purposes.
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| 8. |
- Belov, Ilja, et al.
(author)
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Fin‐Tube and Plate Heat Exchangers : Evaluation of Transient Performance
- 2017
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In: 18th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE). - : IEEE. - 9781509043446 - 9781509043439 - 9781509043453
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Conference paper (peer-reviewed)abstract
- A methodology for evaluation of transient performance of, and comparison between plate heat exchanger and plate-fin-and-tube heat exchanger was developed and realized, including experiment and 3-D simulation. Heat transfer from water to a gas medium was addressed. The heated gas volume was the same for both heat exchanger designs. This was achieved by placing the plate-fin-and-tube heat exchanger into enclosure. The volume average temperature of the gas as function of time was computed. Estimated material cost for the studied designs was at least seven times lower than for the stainless steel plate heat exchanger. The performance of the selected plate-fin-and-tube heat exchanger design was found comparable to the plate heat exchanger, when both fin and tube materials were set to Al, and the enclosure was a light-weight thermal insulator. Transient behavior of the studied heat exchangers should be of interest for micro-grid applications, but also for thermal management in electronic cabinets and data centers.
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| 9. |
- Bengnér, Johannes, et al.
(author)
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Serum amyloid A – A prime candidate for identification of neonatal sepsis
- 2021
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In: Clinical Immunology. - : Elsevier. - 1521-6616 .- 1521-7035. ; 229:108787
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Journal article (peer-reviewed)abstract
- Neonatal sepsis is common, lethal, and hard to diagnose. In combination with clinical findings and blood culture, biomarkers are crucial to make the correct diagnose. A Swedish national inquiry indicated that neonatologists were not quite satisfied with the available biomarkers. We assessed the kinetics of 15 biomarkers simultaneously: ferritin, fibrinogen, granulocyte colony-stimulating factor (G-CSF), interferon (IFN)-γ, interleukin (IL)-1β, −6, −8, −10, macrophage inflammatory protein (MIP)-1β, procalcitonin, resistin, serum amyloid A (SAA), tumor necrosis factor (TNF)-α, tissue plasminogen activator-3 and visfatin. The goal was to observe how quickly they rise in response to infection, and for how long they remain elevated. From a neonatal intensive care unit, newborns ≥28 weeks gestational age were recruited. Sixty-eight newborns were recruited to the study group (SG), and fifty-one to the control group (CG). The study group subjects were divided into three subgroups depending on clinical findings: confirmed sepsis (CSG), suspected sepsis (SSG) and no sepsis. CSG and SSG were also merged into an entire sepsis group (ESG) for sub-analysis. Blood samples were collected at three time-points; 0 h, 12–24 h and 48–72 h, in order to mimic a “clinical setting”. At 0 h, visfatin was elevated in SSG compared to CG; G-CSF, IFN-γ, IL-1β, −8 and − 10 were elevated in SSG and ESG compared to CG, whereas IL-6 and SAA were elevated in all groups compared to CG. At 12–24 h, IL-8 was elevated in ESG compared to CG, visfatin was elevated in ESG and SSG compared to CG, and SAA was elevated in all three groups compared to CG. At 48–72 h, fibrinogen was elevated in ESG compared to CG, IFN-γ and IL-1β were elevated in SSG and ESG compared to CG, whereas IL-8 and SAA were elevated in all three groups compared to CG. A function of time-formula is introduced as a tool for theoretical prediction of biomarker levels at any time-point. We conclude that SAA has the most favorable kinetics regarding diagnosing neonatal sepsis, of the biomarkers studied. It is also readily available methodologically, making it a prime candidate for clinical use.
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| 10. |
- Cenanovic, Mirza
(author)
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Finite element methods for surface problems
- 2017
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Doctoral thesis (other academic/artistic)abstract
- The purpose of this thesis is to further develop numerical methods for solving surface problems by utilizing tangential calculus and the trace finite element method. Direct computation on the surface is possible by the use of tangential calculus, in contrast to the classical approach of mapping 2D parametric surfaces to 3D surfaces by means of differential geometry operators. Using tangential calculus, the problem formulation is only dependent on the position and normal vectors of the 3D surface. Tangential calculus thus enables a clean, simple and inexpensive formulation and implementation of finite element methods for surface problems. Meshing techniques are greatly simplified from the end-user perspective by utilizing an unfitted finite element method called the Trace Finite Element Method, in which the basic idea is to embed the surface in a higher dimensional mesh and use the shape functions of this background mesh for the discretization of the partial differential equation. This method makes it possible to model surfaces implicitly and solve surface problems without the need for expensive meshing/re-meshing techniques especially for moving surfaces or surfaces embedded in 3D solids, so called embedded interface problems. Using these two approaches, numerical methods for solving three surface problems are proposed: 1) minimal surface problems, in which the form that minimizes the mean curvature was computed by iterative update of a level-set function discretized using TraceFEM and driven by advection, for which the velocity field was given by the mean curvature flow, 2) elastic membrane problems discretized using linear and higher order TraceFEM, which makes it straightforward to embed complex geometries of membrane models into an elastic bulk for reinforcement and 3) stabilized, accurate vertex normal and mean curvature estimation with local refinement on triangulated surfaces. In this thesis the basics of the two main approaches are presented, some aspects such as stabilization and surface reconstruction are further developed, evaluated and numerically analyzed, details on implementations are provided and the current state of work is presented.
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| 11. |
- Cenanovic, Mirza
(author)
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Finite element methods on surfaces
- 2015
-
Licentiate thesis (other academic/artistic)abstract
- The purpose of this thesis is to improve numerical simulations of surface problems. Two novel computational concepts are analyzed and applied on two surface problems; minimal surface problems and elastic membrane problems. The concept of tangential projection implies that direct computation on the surface is made possible compared to the classical approach of mapping 2D parametric surfaces to 3D surfaces by means of differential geometry operators. The second concept presented is the cut finite element method, in which the basic idea of discretization is to embed the d- 1-dimensional surface in a d-dimensional mesh and use the basis functions of a higher dimensional mesh but integrate over the surface. The aim of this thesis is to present the basics of the two main approaches and to provide details on the implementation.
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| 12. |
- Ghasemi, Rohollah, 1983-, et al.
(author)
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Abrasion resistance of lamellar graphite iron : Interaction between microstructure and abrasive particles
- 2018
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In: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 120, s. 465-475
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Journal article (peer-reviewed)abstract
- This study focuses on abrasion resistance of Lamellar Graphite Iron (LGI) using microscratch test under constant and progressive load conditions. The interactions between a semi-spherical abrasive particle, cast iron matrix and graphite lamellas were physically simulated using a sphero-conical indenter. The produced scratches were analysed using LOM and SEM to scrutinise the effect of normal load on resulting scratch depth, width, frictional force, friction coefficient and deformation mechanism of matrix during scratching. Results showed a significant matrix deformation, and change both in frictional force and friction coefficient by increase of scratch load. Furthermore, it was shown how abrasive particles might produce deep scratches with severe matrix deformation which could result in graphite lamella's coverage and thereby deteriorate LGI's abrasion resistance.
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| 13. |
- Hansbo, Peter, et al.
(author)
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A discontinuous Galerkin method for cohesive zone modelling
- 2015
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In: Finite elements in analysis and design (Print). - : Elsevier. - 0168-874X .- 1872-6925. ; 102-103, s. 1-6
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Journal article (peer-reviewed)abstract
- We propose a discontinuous finite element method for small strain elasticity allowing for cohesive zone modeling. The method yields a seamless transition between the discontinuous Galerkin method and classical cohesive zone modeling. Some relevant numerical examples are presented. © 2015 Elsevier B.V.
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| 14. |
- Hansbo, Peter, et al.
(author)
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Least-squares stabilized augmented Lagrangian multiplier method for elastic contact
-
Other publication (other academic/artistic)abstract
- In this paper, we propose a stabilized augmented Lagrange multiplier method for the finite element solution of small deformation elastic contact problems. We limit ourselves to friction–free contact with a rigid obstacle, but the formulation is readily extendable to more complex situations.
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| 15. |
- Hansbo, Peter, et al.
(author)
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Least-squares stabilized augmented Lagrangian multiplier method for elastic contact
- 2016
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In: Finite elements in analysis and design (Print). - : Elsevier. - 0168-874X .- 1872-6925. ; 116, s. 32-37
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Journal article (peer-reviewed)abstract
- In this paper, we propose a stabilized augmented Lagrange multiplier method for the finite element solution of small deformation elastic contact problems. We limit ourselves to friction-free contact with a rigid obstacle, but the formulation is readily extendable to more complex situations. © 2016 Elsevier B.V.
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| 16. |
- Högberg, J. Li, et al.
(author)
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Simulation of an adhesive layer using a novel mixed mode cohesive law
- 2006
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In: CDCM 2006 - Conference on Damage in Composite Materials 2006 18th-19th of September 2006 in Stuttgart, Germany.
-
Conference paper (peer-reviewed)abstract
- The purpose of this work is to develop a flexible cohesive law to simulate the constitutive behaviour of an adhesive layer under mixed mode loading. A mixed mode cohesive law that captures the linear elastic and softening behaviour before fracture is presented. This simple model uses a coupled formulation to describe the mixed mode cohesive behaviour. It also allows for different fracture parameters, such as fracture energy, strength and critical separation in different mode mixities. Thus, the fracture process in mode I (peel), in mode II (shear) or in mixed mode (a combination of peel and shear) can be modelled without the usual constraint of a common fracture energy in peel and shear. Examples are given of FE-implementation of the normalised cohesive law, namely for the Unsymmetric Double Cantilever Beam (UDCB) specimen and the Mixed-mode double Cantilever Beam (MCB) specimen. Both specimens are adhesively bonded and loaded in mixed-mode.
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| 17. |
- Jansson, Johan, et al.
(author)
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An anisotropic non-linear material model for glass fibre reinforced plastics
- 2018
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In: Composite structures. - : Elsevier. - 0263-8223 .- 1879-1085. ; 195, s. 93-98
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Journal article (peer-reviewed)abstract
- This paper aims to present a methodology to predict the anisotropic and non-linear behaviour of glass fibre reinforced plastics using finite element methods. A material model is implemented in order to remedy the need of multiple material definitions, and to control the local plastic behaviour as a function of the fibre orientation. Injection moulding simulations traditionally provide second order orientation tensors, which are considered together with a homogenization scheme to compute local material properties. However, in the present study, fourth order tensors are used in combination with traditional methods to provide more accurate material properties. The elastic and plastic response of the material model is optimized to fit experimental test data, until simulations and experiments overlap. The proposed material model can support design engineers in making more informed decisions, allowing them to create smarter products without the need of excessive safety factors, leading to reduced component weight and environmental impact.
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| 18. |
- Jansson, Johan, et al.
(author)
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Image-based semi-multiscale finite element analysis using elastic subdomain homogenization
- 2021
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In: Meccanica (Milano. Print). - : Springer. - 0025-6455 .- 1572-9648. ; 56:11, s. 2799-2811
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Journal article (peer-reviewed)abstract
- In this paper we present a semi-multiscale methodology, where a micrograph is split into multiple independent numerical model subdomains. The purpose of this approach is to enable a controlled reduction in model fidelity at the microscale, while providing more detailed material data for component level- or more advanced finite element models. The effective anisotropic elastic properties of each subdomain are computed using periodic boundary conditions, and are subsequently mapped back to a reduced mesh of the original micrograph. Alternatively, effective isotropic properties are generated using a semi-analytical method, based on averaged Hashin–Shtrikman bounds with fractions determined via pixel summation. The chosen discretization strategy (pixelwise or partially smoothed) is shown to introduce an uncertainty in effective properties lower than 2% for the edge-case of a finite plate containing a circular hole. The methodology is applied to a aluminium alloy micrograph. It is shown that the number of elements in the aluminium model can be reduced by 99.89 % while not deviating from the reference model effective material properties by more than 0.65 % , while also retaining some of the characteristics of the stress-field. The computational time of the semi-analytical method is shown to be several orders of magnitude lower than the numerical one. © 2021, The Author(s).
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| 19. |
- Jansson, Johan
(author)
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Multiscale Constitutive Modeling of Heterogeneous Engineering Materials
- 2021
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Doctoral thesis (other academic/artistic)abstract
- This work deals with different methods used to determine heterogeneous constitutive model parameters for macro-scale finite element models, based on microstructural variations, caused by the manufacturing process. These methods could be applied to decrease modeling errors associated with the material behavior, improving the predictive capabilities of structural analyses in simulation-driven industrial product development. By providing engineers with more sophisticated tools and methods which lets them consider the complex relationships between the manufacturing process, the resulting microstructure and the final properties, manufactured components have the potential to be further optimized with respect to both weight and performance, reducing their cost and environmental impact.An empirical approach for cast components is presented in Papers I & II, where material testing is used as a basis for constitutive model parameter extraction via optimization. Linear models were created for both thermo-mechanical and thermo-physical material properties, by characterizing specimens extracted from different regions in a lamellar graphite cast iron cylinder head. These models were used to generate heterogeneous constitutive model parameters for the cylinder head, based on the solidification time as predicted by casting process simulations. The influence of several commonly made casting-specific engineering simplifications were investigated, and it was shown that non-trivial errors of a potentially large magnitude are introduced by not considering e.g. the compressive behavior of the material, residual stresses from the casting process, the temperature dependency of the material, or the process-induced heterogeneity.Paper III describes a statistical homogenization-based method, for modeling of anisotropic fiber reinforced materials. A non-linear anisotropic constitutive model was developed and implemented in commercial finite element codes, which is able to consider heterogeneous fiber orientations using only one material definition. The anisotropic elastic constitutive tensor is determined from fiber-matrix homogenization, and orientation averaging using second- and fourth order fiber orientation tensors provided by injection molding simulations. The plastic constitutive parameters are determined by optimization against experimental tensile tests using specimens with different fiber orientations. The method was demonstrated using a injection molded 50 wt.% short glass fiber reinforced plastic.A pixel/voxel-based method is presented in Papers IV (2D) & V (3D), for simple and efficient generation of reduced numerical microstructure models using imaging data as input. The input micrograph or image stack is split into subdomains, which are evaluated individually using numerical or semi-analytical homogenization. The constitutive tensor of each subdomain is mapped to a new, reduced numerical model. The purpose of this approach was to support component level analyses, by representing process-induced microstructural imperfections like e.g. porosity on the macro-scale, in a computationally efficient way. The geometrical description of the microstructure can be retrieved from experimental imaging methods like Scanning Electron Microscopy (SEM) or X-ray based Computed Tomography (CT). Alternatively, it can be approximated from phase field or manufacturing process simulations. The method was demonstrated by reducing a 2D aluminium micrograph by 99.89%, with material property errors of less than 0.5% in Paper IV. Also, in paper V by reducing a complex high-resolution 3D aluminum shrinkage porosity by 99.2%, with a material property error of approximately 1%. The method significantly reduces the complexity of building finite element models of complex microstructures, where the pre-processing step is replaced by image segmentation.
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| 20. |
- Jansson, Johan, et al.
(author)
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On the use of heterogeneous thermomechanical and thermophysical material properties in finite element analyses of cast components
- 2019
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In: Joint 5th International Conference on Advances in Solidification Processes (ICASP-5) & 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5) 17–21 June 2019, Salzburg, Austria. - : Institute of Physics Publishing (IOPP).
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Conference paper (peer-reviewed)abstract
- Cast components generally show a heterogeneous distribution of material properties, caused by variations in the microstructure that forms during solidification. Variations caused by the casting process are not commonly considered in structural analyses, which might result in manufacturing of sub-optimised components with unexpected in-use behaviour. In this paper, we present a methodology which can be used to consider both thermomechanical and thermophysical variations using finite element analyses in cast components. The methodology is based on process simulations including microstructure modelling and correlations between microstructural features and material properties. Local material data are generated from the process simulation results, which are integrated into subsequent structural analyses. In order to demonstrate the methodology, it is applied to a cast iron cylinder head. The heterogeneous distribution of material properties in this component is investigated using experimental methods, demonstrating local variations in both mechanical and physical behaviour. In addition, the strength-differential effect on tensile and compressive behaviour of cast iron is considered in the modelling. The integrated simulation methodology presented in this work is relevant to both design engineers, production engineers as well as material scientists, in order to study and better understand how local variations in microstructure might influence the performance and behaviour of cast components under in-use conditions.
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| 21. |
- Jansson, Johan
(author)
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Process-Induced Local Material Variations in Finite Element Simulations of Cast and Fibre Reinforced Injection Moulded Components
- 2019
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Licentiate thesis (other academic/artistic)abstract
- The purpose of this thesis is to provide an overview of the methods used in the appended papers, in order to consider heterogeneous material properties in finite element simulations by using process simulations as input. The work deals with both injection moulded and cast components, and focuses on process-induced local material variations and their effect on component performance.The influence of heterogeneous properties originating from the casting process as well as some other common simplifications, which are made in finite element analyses, are evaluated for a cast iron component. It is found that commonly neglected properties such as compressive strength, residual stresses, temperature dependency and heterogeneous properties have a non-trivial and potentially large influence on the simulation results.Lastly, a computational method for fibre reinforced plastics is presented. The methodology enables designers to consider the non-linear anisotropic properties of fibre-reinforced polymers, due to the flow-induced fibre orientation predicted by injection moulding simulations. The method allows material data assignment in each integration-point of the structural mesh. The method is demonstrated to capture the behaviour of the full range of fibre orientations simultaneously with good accuracy.
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| 22. |
- Jansson, Johan, et al.
(author)
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Simulation-driven product development of cast components with allowance for process-induced material behaviour
- 2020
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In: Journal of Computational Design and Engineering. - : Oxford University Press. - 2288-5048. ; 7:1, s. 78-85
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Journal article (peer-reviewed)abstract
- This paper presents a methodology that can be used to consider local variations in thermomechanical and thermophysical material properties, residual stresses, and strength-differential effects in finite element analyses of cast components. The methodology is based on applying process simulations and structural analyses together with experimentally established, or already available literature data, in order to describe element-specific material variations. A cast-iron cylinder head was used in order to evaluate the influence of several simplifications that are commonly performed in computer aided engineering. It is shown that non-trivial errors of a potentially large magnitude are introduced by not considering residual stresses, compressive behaviour, temperature dependence, and process-induced material property variations. By providing design engineers with tools that allow them to consider the complex relationships between these aspects early in the development phase, cast components have the potential to be further optimized with respect to both weight and performance.
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| 23. |
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| 24. |
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| 25. |
- Kasvayee, Keivan Amiri, 1986-, et al.
(author)
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Microstructural strain distribution in ductile iron; Comparison between finite element simulation and digital image correlation measurements
- 2015
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Reports (other academic/artistic)abstract
- This paper presents a study on micro-scale deformation and the effect of microstructure on localised deformation of ductile iron, utilizing in-situ tension testing, digital image correlation (DIC) and finite element analysis (FEA). A tensile stage integrated with an optical microscope was used to acquire a series of micrographs during the tensile test. Applying DIC and an etched speckle pattern, a high resolution local strain field was measured in the microstructure. In addition, a finite element (FE) model was used to predict the strain maps. The materials parameters were optimized based on Ramberg-Osgood model. The DIC and simulation strain maps conformed to a large extent resulting in the verification of the model in micro-scale level. It was found that the Ramberg-Osgood theory can be used to capture the main trends of strain localization. The discrepancies between the simulated and DIC results were explained based on microstructure dimensionality, differences in spatial resolution and uncertainty in the FE-model.
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| 26. |
- Kasvayee, Keivan Amiri, et al.
(author)
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Microstructural strain distribution in ductile iron; comparison between finite element simulation and digital image correlation measurements
- 2016
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In: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 655, s. 27-35
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Journal article (peer-reviewed)abstract
- This paper presents a study on microstructural deformation of a ferritic-pearlitic ductile iron, utilizing in-situ tensile testing, digital image correlation (DIC) and finite element analysis (FEA). For this purpose, the in-situ tensile test and DIC were used to measure local strain fields in the deformed microstructure. Furthermore, a continuum finite element (FE) model was used to predict the strain maps in the microstructure. Ferrite and pearlite parameters for the FE-model were optimized based on the Ramberg-Osgood relation. The DIC and simulation strain maps were compared qualitatively and quantitatively. Similar strain patterns containing shear bands in identical locations were observed in both strain maps. The average and localized strain values of the DIC and simulation conformed to a large extent. It was found that the Ramberg-Osgood model can be used to capture the main trends of strain localization. The discrepancies between the simulated and DIC results were explained based on the; (i) subsurface effect of the microstructure; (ii) differences in the strain spatial resolutions of the DIC and simulation and (iii) abrupt changes in strain prediction of the continuum FE-model in the interface of the phases due to the sudden changes in the elastic modulus. © 2015 Elsevier B.V.
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| 27. |
- Kasvayee, Keivan Amiri, 1986-, et al.
(author)
-
Microstructural strain localization and crack evolution in ductile iron
- 2015
-
Reports (other academic/artistic)abstract
- This paper focuses on the deformation and crack evolution in ductile iron under tension, investigated by coupled in-situ tensile test and finite element simulation. Micro-crack initiation and development were tracked at the microstructure level. The local strain around micro-cracks were measured by using Digital Image Correlation (DIC). The results obtained from the experiments were compared to a finite element model including cohesive elements to enable crack propagation. The resulting local strains were analyzed in connection to the observed micro-crack incidents in both DIC and simulation. The predictions of the finite element model showed good agreement with those obtained from the experiment, in the case of early decohesion, the amplitude of the strain localization and macroscopic stress-strain behavior. The results revealed that decohesion was commonly initiated early around graphite surrounded by ferrite which was identified as high strain regions. By increasing the global deformation, micro-cracks initiated in these areas and propagated but were arrested within the ferrite zone due to strain hardening and stress shielding of pearlite. Both the DIC and the simulation revealed that irregular shaped graphite were more susceptible to strain localization and micro-crack initiation. It could be observed that the cohesive model was able to capture the main trends of localized plastic deformation and crack initiation
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| 28. |
- Kasvayee, Keivan Amiri, 1986-, et al.
(author)
-
Microstructural strain mapping during in-situ cyclic testing of ductile iron
- 2018
-
In: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 140, s. 333-339
-
Journal article (peer-reviewed)abstract
- This paper focuses on local strain distribution in the microstructure of high silicon ductile iron during cyclic loading. In-situ cyclic test was performed on compact-tension (CT) samples inside the scanning electron microscope (SEM) to record the whole deformation and obtain micrographs for microstructural strain measurement by means of digital image correlation (DIC) technique. Focused ion beam (FIB) milling was used to generate speckle patterns necessary for DIC measurement. The equivalent Von Mises strain distribution was measured in the microstructure at the maximum applied load. The results revealed a heterogeneous strain distribution at the microstructural level with higher strain gradients close to the notch of the CT sample and accumulated strain bands between graphite particles. Local strain ahead of the early initiated micro-cracks was quantitatively measured, showing high strain localization, which decreased by moving away from the micro-crack tip. It could be observed that the peak of strain in the field of view was not necessarily located ahead of the micro-cracks tip which could be because of the (i) strain relaxation due to the presence of other micro-cracks and/or (ii) presence of subsurface microstructural features such as graphite particles that influenced the strain concentration on the surface.
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| 29. |
- Kasvayee, Keivan Amiri, 1986-, et al.
(author)
-
Strain localization and crack formation effects on stress-strain response of ductile iron
- 2017
-
In: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 702, s. 265-271
-
Journal article (peer-reviewed)abstract
- The strain localization and crack formation in ferritic-pearlitic ductile iron under tension was investigated by in-situ tensile tests. In-situ tensile tests under optical microscope were performed and the onset of the early ferrite-graphite decohesions and micro-cracks inside the matrix were studied. The results revealed that early ferrite-graphite decohesion and micro-cracks inside the ferrite were formed at the stress range of 280–330 MPa, where a kink occurred in the stress-strain response, suggesting the dissipation of energy in both plastic deformation and crack initiation. Some micro-cracks initiated and propagated inside the ferrite but were arrested within the ferrite zone before propagating in the pearlite. Digital Image Correlation (DIC) was used to measure local strains in the deformed micrographs obtained from the in-situ tensile test. Higher strain localization in the microstructure was measured for the areas in which the early ferrite-graphite decohesions occurred or the micro-cracks initiated. © 2017 Elsevier B.V.
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| 30. |
- Meena, Akash, et al.
(author)
-
Numerical and experimental study of the variation of keyhole depth with an aluminum alloy (AA1050)
- 2024
-
In: Journal of Advanced Joining Processes. - : Elsevier. - 2666-3309. ; 9
-
Journal article (peer-reviewed)abstract
- The keyhole depth is a key measurement characteristic in the laser welding of busbar to battery tabs in battery packs for electric vehicles (EV), as it directly affects the quality of the weld. In this work, experiments are carried out with controlled and adjusted laser power and feed rate parameters to investigate the influence on the keyhole width, keyhole depth and porosities. A 3D numerical model of laser keyhole welding of an aluminum alloy (A1050) has been developed to describe the porosity formation and the keyhole depth variation. A new integration model of the recoil pressure and the rate of evaporation model is implemented which is closer to the natural phenomena as compared to the conventional methods. Additionally, major physical forces are employed including plume formation, upward vapor pressure and multiple reflection in the keyhole. The results show that keyhole depth is lower at higher feed rate, while lower feed rates result in increased keyhole depth. This study reveals that low energy densities result in an unstable keyhole with high spattering, exacerbated by increased laser power. Mitigating incomplete fusion is achieved by elevating laser energy density. The findings emphasize the critical role of keyhole depth in optimizing laser welding processes for applications like busbar-to-battery tab welding.
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| 31. |
- Olofsson, Jakob, et al.
(author)
-
A methodology for microstructure-based structural optimization of cast and injection moulded parts using knowledge-based design automation
- 2017
-
In: Advances in Engineering Software. - : Elsevier. - 0965-9978 .- 1873-5339. ; 109, s. 44-52
-
Journal article (peer-reviewed)abstract
- The local material behaviour of cast metal and injection moulded parts is highly related to the geometrical design of the part as well as to a large number of process parameters. In order to use structural optimization methods to find the geometry that gives the best possible performance, both the geometry and the effect of the production process on the local material behaviour thus has to be considered. In this work, a multidisciplinary methodology to consider local microstructure-based material behaviour in optimizations of the design of engineering structures is presented. By adopting a knowledge based industrial product realisation perspective combined with a previously presented simulation strategy for microstructure-based material behaviour in Finite Element Analyses (FEA), the methodology integrates Computer Aided Design (CAD), casting and injection moulding simulations, FEA, design automation and a multi-objective optimization scheme into a novel structural optimization method for cast metal and injection moulded polymeric parts. The different concepts and modules in the methodology are described, their implementation into a prototype software is outlined, and the application and relevance of the methodology is discussed.
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| 32. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Modelling and simulations of ductile iron solidification-induced variations in mechanical behaviour on component and microstructural level
- 2015
-
In: MCWASP XIV. - London : Institute of Physics Publishing (IOPP). ; , s. 1-8, s. 1-8
-
Conference paper (peer-reviewed)abstract
- The mechanical behaviour and performance of a ductile iron component is highly dependent on the local variations in solidification conditions during the casting process. Here we show a framework which combine a previously developed closed chain of simulations for cast components with a micro-scale Finite Element Method (FEM) simulation of the behaviour and performance of the microstructure. A casting process simulation, including modelling of solidification and mechanical material characterization, provides the basis for a macro-scale FEM analysis of the component. A critical region is identified to which the micro-scale FEM simulation of a representative microstructure, generated using X-ray tomography, is applied. The mechanical behaviour of the different microstructural phases are determined using a surrogate model based optimisation routine and experimental data. It is discussed that the approach enables a link between solidification- and microstructure-models and simulations of as well component as microstructural behaviour, and can contribute with new understanding regarding the behaviour and performance of different microstructural phases and morphologies in industrial ductile iron components in service.
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| 33. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Multidisciplinary shape optimization of ductile iron castings by considering local microstructure and material behaviour
- 2018
-
In: Structural and multidisciplinary optimization (Print). - : Springer. - 1615-147X .- 1615-1488. ; 57:5, s. 1889-1903
-
Journal article (peer-reviewed)abstract
- During the casting process and solidification of ductile iron castings, a heterogeneous microstructure is formed throughout the casting. This distribution is strongly influenced by the item geometry and the process related factors, as chemical composition and local solidification conditions. Geometrical changes to the geometry of the casting thus alters the local mechanical behavior and properties, as well as the distribution of stresses and strains when the casting is subjected to load. In order to find an optimal geometry, e.g. with reduced weight and increased load-bearing capacity, this interdependency between geometry and local material behavior needs to be considered and integrated into the optimization method. In this contribution, recent developments in the multidisciplinary integration of casting process simulation, solidification and microstructure modelling, microstructure-based material characterization, finite element structural analyses with local material behavior and structural optimization techniques are presented and discussed. The effect and relevance of considering the local material behavior in shape optimization of ductile iron castings is discussed and evidenced by an industrial application. It is shown that by adopting a multidisciplinary optimization approach by integration of casting simulation and local material behavior into shape optimization, the potential of the casting process to obtain components with high performance and reliability can be enabled and utilized.
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| 34. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Multidisciplinary shape optimization of ductile iron castings byconsidering local microstructure and material behaviour
- 2017
-
In: WCSMO12, 12th World Congress of Structural and Multidisciplinary Optimisation. - : Technische Universität. ; , s. 82-, s. 82-
-
Conference paper (peer-reviewed)abstract
- During the casting process and solidification of ductile iron castings, a heterogeneous microstructure is formed throughout the casting. This distribution is highly controlled by process related factors, as chemical composition, local solidification conditions, and the geometry of the casting. Geometrical changes to the geometry of the casting thus alters the local mechanical behaviour, as well as the distribution of stresses and strains when the casting is subjected to load. In order to find an optimal geometry, e.g. with reduced weight and increased load-bearing capacity, this interdependency between geometry and local material behaviour needs to be considered and integrated into the optimization method. In this contribution, recent developments in the multidisciplinary integration of casting process simulation, solidification and microstructure modelling, microstructure-based material characterization, Finite Element Analyses (FEA) with local material behaviour and structural optimization techniques are presented and discussed. The effect and relevance of considering the local material behaviour in shape optimization of ductile iron castings is discussed and evidenced by an industrial application. It is shown that by adopting a multidisciplinary optimization approach by integration of casting simulation and local material behaviour into shape optimization, the potential of the casting process to obtain components with high performance and reliability can be enabled and utilized.
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| 35. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
The multi-scale closed chain of simulations – incorporating local variations in microstructure into finite element simulations
- 2016
-
In: TMS 2015 144th Annual Meeting & Exhibition. - Cham : Springer International Publishers, Switzerland. - 9783319486086 - 9783319481272 ; , s. 1057-1064
-
Conference paper (peer-reviewed)abstract
- Numerical simulations of component behavior and performance is critical to develop optimized and robust load-bearing components. The reliability of these simulations depend on the description of the components material behavior, which for e.g. cast and polymeric materials exhibit component specific local variations depending on geometry and manufacturing parameters. Here an extension of a previously presented strategy, the closed chain of simulations for cast components, to predict and incorporate local material data into Finite Element Method (FEM) simulations on multiple scales is shown. Manufacturing process simulation, solidification modelling, material characterization and representative volume elements (RVE) provides the basis for a microstructure-based FEM analysis of component behavior and a simulation of the mechanical behavior of the local microstructure in a critical region. It is discussed that the strategy is applicable not only to cast materials but also to injection molded polymeric materials, and enables a common integrated computational microstructure-based approach to optimized components.
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| 36. |
- Olofsson, Jakob, 1980-, et al.
(author)
-
Three-dimensional study of nodule clustering and heterogeneous strain localization for tailored material properties in ductile iron
- 2019
-
In: Joint 5th International Conference on Advances in Solidification Processes (ICASP-5) & 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5) 17–21 June 2019, Salzburg, Austria. - : Institute of Physics Publishing (IOPP).
-
Conference paper (peer-reviewed)abstract
- Tailored heterogeneous distributions of microstructural features enable extraordinary material performance in biological and physiological structures such as trees, the aortic arch, human teeth and dinosaur skulls. In ductile iron, a heterogeneous distribution in size and morphology of graphite nodules and variations of the fractions of ferrite and pearlite are created during solidification, and varies as a function of parameters such as local cooling rate, segregation and flow. In the current work, the size distribution as well as the orientation and relation between graphite nodules is obtained by a three-dimensional reconstruction of a ductile iron microstructure from X-ray tomography. The effect of the nodule morphology and clustering on the localization of plastic strains is studied numerically using finite element analysis of the reconstructed microstructure. Real castings have a variation in geometry, solidification conditions and are subjected to variations in loads. A framework for optimized geometry and solidification conditions in order to design and deliver castings with tailored local material performance is proposed.
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| 37. |
- Pesämaa, Ossi, et al.
(author)
-
Attitudes to change in Gnosjöregion
- 2009
-
In: Presented at The international Symposium on Entrepreneurship in Tourism, Rovaniemi, Finland, March 17-21, 2009.
-
Conference paper (other academic/artistic)abstract
- This study promotes ideas into two main academic areas, that is attitudes towards change processes and regional development. The implications of the study are written to tourism in the Gnosjöregion and other countryside areas. We specifically ask what attitudes towards change processes in development projects in tourism generate commitments to tourism and to what extent these effects are moderated by perceived involvement. Our objective is to develop more knowledge to the area of attitudes within project management. The results of the study engender from a pre-study from 59 responses of a survey distributed during spring 2008 in the Gnosjöregion. Our major implication is that future study may consider freedom rather than interest towards working in change processes and that these effects are also moderated when individuals perceive an enhanced involvement. Our study is a first attempt to develop these two areas and results should therefore be read and interpreted with the same carefulness as any pre-study is prepared and conducted.
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| 38. |
- Rashid, Asim, et al.
(author)
-
Simulation of internal mechanical conditions in the lower limb donned in a transtibial prosthetic socket
-
Other publication (other academic/artistic)abstract
- This paper investigates the internal mechanical conditions in a transtibial cross-section while in contact with a prosthetic socket. The nite element model considers the nonlinear behaviors of individual soft tissues instead of lumping them together. The contact problem is solved between socket and limb while taking the friction into consideration to determine the contact forces and resultant internal stress-strain in the limb. Simulation results are presented for three dierent socket designs; total contact, total surface-bearing and hydrostatic sockets. Inuence of higher blood pressure on internal mechanical conditions is also explored.
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| 39. |
- Salomonsson, Kent, et al.
(author)
-
An adhesive interphase element for structural analyses
- 2008
-
In: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 76:4, s. 482-500
-
Journal article (peer-reviewed)abstract
- A special purpose finite element is developed for structural simulations of complex adhesively bonded structures. In the interphase element, the adhesive is explicitly regarded as a material phase between two substrates. The element considers large rotations. Furthermore. it considers in-plane straining of the adhesive due to large curvatures of the bonded shells. This feature appears especially important when considering bonding of thin plastically deforming metallic shell structures. Simulations are made on specimens where the adherends deform both elastically and plastically. The results are in good agreement with previously performed experiments. Copyright (0 2008 John Wiley & Sons, Ltd.
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| 40. |
- Salomonsson, Kent, et al.
(author)
-
Analysis of Localized Plastic Strain in Heterogeneous Cast Iron Microstructures Using 3D Finite Element Simulations
- 2017
-
In: Proceedings of the 4th World Congress on Integrated Computational Materials Engineering (ICME 2017). - Cham : Springer. - 9783319578637 - 9783319578644 ; , s. 217-225
-
Conference paper (peer-reviewed)abstract
- The design and production of light structures in cast iron with high static and fatigue performance is of major interest in e.g. the automotive area. Since the casting process inevitably leads to heterogeneous solidification conditions and variations in microstructural features and material properties, the effects on multiple scale levels needs to be considered in the determination of the local fatigue performance. In the current work, microstructural features of different cast irons are captured by use of micro X-ray tomography, and 3D finite element models generated. The details of the 3D microstructure differ from the commonly used 2D representations in that the actual geometry is captured and that there is not a need to compensate for 3D-effects. The first objective with the present study is to try and highlight certain aspects at the micro scale that might be the underlying cause of fatigue crack initiation, and ultimately crack propagation, under fatigue loading for cast iron alloys. The second objective is to incorporate the gained knowledge about the microstructural behavior into multi-scale simulations at a structural length scale, including the local damage level obtained in the heterogeneous structure subjected to fatigue load.
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| 41. |
- Salomonsson, Kent, et al.
(author)
-
Analysis of the Internal Mechanical Conditions in the Lower Limb Due to External Loads
- 2016
-
In: World Academy of Science, Engineering and Technology, International Science Index, International Journal of Medical, Health, Biomedical, Bioengineering and Pharmaceutical Engineering. - London. ; , s. 288-293
-
Conference paper (peer-reviewed)abstract
- Human soft tissue is loaded and deformed by any activity, an effect known as a stress-strain relationship, and is often described by a load and tissue elongation curve. Several advances have been made in the fields of biology and mechanics of soft human tissue. However, there is limited information available on in vivo tissue mechanical characteristics and behavior. Confident mechanical properties of human soft tissue cannot be extrapolated from e.g. animal testing. Thus, there is need for non invasive methods to analyze mechanical characteristics of soft human tissue. In the present study, the internal mechanical conditions of the lower limb, which is subject to an external load, is studied by use of the finite element method. A detailed finite element model of the lower limb is made possible by use of MRI scans. Skin, fat, bones, fascia and muscles are represented separately and the material properties for them are obtained from literature. Previous studies have been shown to address macroscopic deformation features, e.g. indentation depth, to a large extent. However, the detail in which the internal anatomical features have been modeled does not reveal the critical internal strains that may induce hypoxia and/or eventual tissue damage. The results of the present study reveals that lumped material models, i.e. averaging of the material properties for the different constituents, does not capture regions of critical strains in contrast to more detailed models.
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| 42. |
- Salomonsson, Kent E., et al.
(author)
-
Weighted Potential Methodology for Mixed Mode Cohesive Laws
- 2010
-
In: Proceedings of the MECOM DEL BICENTENARIO, IX Argentinian Congress on Computational Mechanics. - : Asociación Argentina de Mecánica Comptacional. ; , s. 8355-8374
-
Conference paper (peer-reviewed)abstract
- A weighted potential methodology is developed by utilizing pure mode I and mode II energy release rate experiments to determine the traction-separation relations for thin adhesive layers. The experimentally measured energy release rates act as boundary conditions for developing a weighted potential function. Thus, the tractions for any mixed mode loading can be established. Changes of mode mix during an experiment can also be captured by the law since every mixed mode variation is given by the potential function. Furthermore, by use of an inverse J-integral approach and damage type variables, the traction-separation relations for any mode mix can be approximated by use of pure mode experiments. Numerical simulations show the applicability of the methodology. The results indicate that the methodology is promising when simulating the constitutive behavior of adhesive layers.
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| 43. |
- Salomonsson, Kent, et al.
(author)
-
Influence of root curvature on the fracture energy of adhesive layers
- 2009
-
In: Engineering Fracture Mechanics. - : Elsevier. - 0013-7944 .- 1873-7315. ; 76:13, s. 2025-2038
-
Journal article (peer-reviewed)abstract
- Previously performed experiments to study the mode I behavior of an adhesive layer revealed an apparent increase in the fracture toughness when the adherends deformed plastically. Attempts to simulate the experiments are made; both with elastically and plastically deforming adherends. Thus, effects of the size of the process zone and the deformation of the adherends are revealed. The adhesive layer is modeled using finite elements with different approaches; cohesive elements and representative volume elements. The adherends are modeled with solid elements. With a long process zone, all models give good results as compared to the experiments. However, only the model with representative volume elements gives good agreement for large root curvatures and correspondingly short process zones. The results are interpreted by analyzing the deformation and mechanisms of crack propagation in the representative volume elements. It is shown that with large root curvature of the adherends, the in-plane stretching of the adhesive layer gives a substantial contribution to the fracture energy. A simple formula is derived and shown to give an accurate prediction of the effects of the root curvature. This result indicates the limits of conventional cohesive zone modeling of an adhesive layer of finite thickness.
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| 44. |
- Salomonsson, Kent
(author)
-
Meso-Mechanical Modeling and Analysis of Adhesive Layers
- 2007
-
Doctoral thesis (other academic/artistic)abstract
- This thesis is concerned with the modeling, simulation and analysis of adhesive layers. By use of an in situ scanning electron microscopy study it is found that the adhesive studied in the present thesis has a very complex structure with two different compounds, a mineral and an epoxy/thermoplastic blend. A representative volume element (RVE) model is developed to study the behavior of the adhesive layer at the meso-level. It is a continuum model where interface finite elements are implemented at the boundaries of the continuum elements in order to enable crack initiation and propagation of micro cracks. On a structural level, two deformation modes, modes I and II, dominate the behavior of thin adhesive layers. With the RVE it is possible reproduce experimental stress-deformation relations from both modes. However, in a real structure, mixed mode loading usually occur. A range of mode mixes is studied, using the RVE, from an un-loaded state until fracture of the layer. The results indicate that the behavior of the interface elements dominate for mode mixes close to mode I and plasticity in the continuum elements dominates for mode II dominated mode mixes. Furthermore, effects of large root curvatures of the adherends is analyzed numerically by simulating plastically deforming double cantilever beam specimens using the finite element model. The developed RVE is implemented in the models to simulate the behavior of the adhesive layer. By this methodology, virtual experiments can be analyzed with extreme detail. It is shown that in-plane straining of the adhesive layer significantly influences the strength of adhesive joints at large plastic strain of the adherends. There is a never ending need in industries to minimize computational time. To this end, an interphase finite element for structural analyses is developed. The element considers in-plane straining of the adhesive layer due to large curvatures of surrounding substrates.
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| 45. |
- Salomonsson, Kent
(author)
-
Meso-Mechanical Modeling of Thin Adhesive Layers
- 2005
-
Licentiate thesis (other academic/artistic)abstract
- A thin adhesive layer is analyzed using a representative volume element (RVE). The RVE is comprised by, both continuum and interfacial finite elements. The interface elements allow for crack initiation and crack propagation. To obtain realistic results from the RVE simulation, an in situ scanning electron microscopy (SEM) study is performed. Results from the SEM study show that the adhesive has a very complex structure with two different compounds, a mineral and an epoxy/thermoplastic blend.The RVE is subjected to two different load cases, peel and shear. An evolutionary algorithm is used to calibrate the numerical model to experimental results. The simulation results are compared to experimental results to verify the numerical model. The simulations show good agreement with the experimental results for both the peel and shear experiments.
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| 46. |
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| 47. |
- Salomonsson, Kent
(author)
-
Mixed mode modeling of a thin adhesive layer using a meso-mechanical model
- 2008
-
In: Mechanics of materials. - : Elsevier. - 0167-6636 .- 1872-7743. ; 40:8, s. 665-672
-
Journal article (peer-reviewed)abstract
- A representative volume element is modeled using the finite element method. It is used to analyze mixed mode behavior of a thin adhesive layer. Two sources of dissipation is modeled; plasticity and decohesion. Macroscopic traction–separation laws are extracted from the simulations. The results indicate that a boundary of mode mix exists between a region where major plastic dissipation is present and a region where it is not. Without major plastic dissipation, the fracture energy is low and essentially governed by the cohesive properties. This is the case in peel dominated loading cases. In shear dominated loading cases plastic dissipation gives a substantial contribution to the fracture energy. The results show that pure shear loading gives the largest fracture energy.
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| 48. |
- Salomonsson, Kent, et al.
(author)
-
Modeling and Analysis of a Screw Fitting Assembly Process Involving a Cast Magnesium Component
- 2020
-
In: Frontiers in Materials. - : Frontiers Media S.A.. - 2296-8016. ; 7
-
Journal article (peer-reviewed)abstract
- A finite element analysis of a complex assembly was made. The material description used was a physically based material model with dislocation density as an internal state variable. This analysis showed the importance of the materials’ behavior in the process as there is discrepancy between the bolt head contact pressure and the internals state of the materials where the assembly process allows for recovery. The end state is governed by both the tightening process and the thermal history and strongly influenced by the thermal expansion of the AZ91D alloy.
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| 49. |
- Salomonsson, Kent, et al.
(author)
-
Modeling and parameter calibration of an adhesive layer at the meso level
- 2008
-
In: Mechanics of materials. - : Elsevier ltd.. - 0167-6636 .- 1872-7743. ; 40:1-2, s. 48-65
-
Journal article (peer-reviewed)abstract
- A mesomechanical finite element model of a thin adhesive layer is developed. The model is calibrated to previously performed experiments. In these, the adhesive layer is loaded in monotonically increasing peel or shear. An in situ SEM study is also performed and used to guide the modeling and calibration. The purpose of the mesomechanical finite element model is to facilitate the development of constitutive laws for adhesive layers. The modeling is based on Xu and Needleman’s method where all continuum finite elements are surrounded by interface elements that allow for the development of micro cracks. Thus, this enables the modeling of the entire process of degradation and fracture of the adhesive layer. A genetic algorithm is developed for the calibration. The simulations show good agreement with the experiments.
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| 50. |
- Salomonsson, Kent, et al.
(author)
-
On the apparent influence of the adherends on the fracture toughness of adhesive layers
- 2007
-
In: Interface design of polymer matrix composites. - 9788755036260
-
Conference paper (peer-reviewed)abstract
- A detailed model of experiments with the double cantilever beam specimen is set up. Analysis of the model shows that an experimentally deduced apparent increase of fracture energy with severely deforming adherends is due to contributions of in-plane straining of the adhesive layer to the fracture energy. An analysis with the J-integral confirms the result.
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