Papers by Larsgunnar Nilsson
Scandinavian Journal of Metallurgy, 1983
In the analysis the material is treated as plastic fracturing. A continuum approach to tensile fr... more In the analysis the material is treated as plastic fracturing. A continuum approach to tensile fracturing is related to fracture mechanical concepts. The rate of strain-softening is obtained from the rate of fracture energy being released. Material anisotropy due to the formation of crack-planes is accounted for. The proposed strain-softening tensile fracturing model is implemented in a finite element program for wave propagation analysis. The strain-softening model is compared to an ideal brittle model in analysis of wave propagation in a concrete rod.
When designing a complex product, many groups are concurrently developing different parts or aspe... more When designing a complex product, many groups are concurrently developing different parts or aspects of the product using detailed simulation models. Multidisciplinary design optimization (MDO) has its roots within the aerospace industry and can effectively improve designs through simultaneously considering different aspects of the product. The groups involved in MDO need to work autonomously and in parallel, which influence the choice of MDO method. The methods can be divided into single-level methods that have a central optimizer making all design decisions, and multi-level methods that have a distributed decision process. This report is a comprehensive summary of the field of MDO with special focus on structural optimization for automotive applications using metamodels. Metamodels are simplified models of the computationally expensive detailed simulation models and can be used to relieve some of the computational burden during MDO studies. The report covers metamodel-based design optimization including design of experiments, variable screening, metamodels and their validation, as well as optimization methods. It also includes descriptions of several MDO methods, along with a comparison between the aerospace and automotive industries and their applications of MDO. The information in this report is based on an extensive literature survey, but the conclusions drawn are influenced by the authors' own experiences from the automotive industry. The trend goes towards using advanced metamodels and global optimization methods for the considered applications. Further on, many of the MDO methods developed for the aerospace industry are unsuitable for the automotive industry where the disciplines are more loosely coupled. The expense of using multi-level optimization methods is then greater than the benefits, and the authors therefore recommend single-level methods for most automotive applications.
Springer eBooks, 1983
Nonlinear wave propagation in plastic fracturing materials : a constitutive modelling and finite ... more Nonlinear wave propagation in plastic fracturing materials : a constitutive modelling and finite element analysis
Godkänd; 1980; 20080507 (ysko
Bond failure in reinforced concrete under monotonic and cyclic loading : a fracture mechanics app... more Bond failure in reinforced concrete under monotonic and cyclic loading : a fracture mechanics approach
International Journal of Automotive and Mechanical Engineering, Mar 30, 2017
Multidisciplinary design optimisation (MDO) can be used as an effective tool to improve the desig... more Multidisciplinary design optimisation (MDO) can be used as an effective tool to improve the design of automotive structures. Large-scale MDO problems typically involve several groups who must work concurrently and autonomously in order to make the solution process efficient. In this article, the formulations of existing MDO methods are compared and their suitability is assessed in relation to the characteristics of automotive structural applications. Both multi-level and single-level optimisation methods are considered. Multi-level optimisation methods distribute the design process but are complex. When optimising automotive structures, metamodels are often required to relieve the computational burden of detailed simulation models. The metamodels can be created by individual groups prior to the optimisation process, and thus offer a way of distributing work. Therefore, it is concluded that a single-level method in combination with metamodels is the most straightforward way of implementing MDO into the development of automotive structures. If the benefits of multi-level optimisation methods, in a special case, are considered to compensate for their drawbacks, analytical target cascading has a number of advantages over collaborative optimisation, but both methods are possible choices.
Adaptive Finite Element Simulation of Sheet Metal Forming Process Using Gradient Based Indicators
Journal of Computer Applications in Technology, 2014
Computer simulation of crash events has become a valuable and necessary tool in the design and im... more Computer simulation of crash events has become a valuable and necessary tool in the design and improvement of automotive structures for better crashworthiness behaviour. Crashworthiness analysis has evolved through rapid improvements in computer technology, as well as through theoretical improvements in solid mechanics concerning large deformation dynamics and contact. Significant applications involve full car analysis such as frontal, rear, and side impact, as well as the analysis of components such as longitudinal beams, steering wheel systems, knee bolsters, seat belts and airbag–dummy interaction. The theoretical background needed in crashworthiness analysis is outlined. Current capabilities are shown on real applications; limitations and future technologies are discussed.
FEMP : an interactive, graphic finite element program for small and large computer systems : veri... more FEMP : an interactive, graphic finite element program for small and large computer systems : verification and demonstration manual
International Journal of Crashworthiness, 2002
ABSTRACT
This paper explores simulation techniques for airbag inflation using a coupled fluid-structure ap... more This paper explores simulation techniques for airbag inflation using a coupled fluid-structure approach. The application is to be seen as an initial study on the phenomena occurring in an airbag during an Out of Position occupant impact. The application problem is an airbag that is set to impact a head form. The head form is positioned at a very short distance from the airbag. A Multi Material Arbitrary Lagrangian Eulerian technique in LS-DYNA is used for the fluid and it is coupled to the fabric structure using a penalty based fluid structure contact algorithm. The results of the head form acceleration and velocity show good agreement to the corresponding experimental results. The results also show that at the early stages of the inflation a high-pressure zone is built up between the inflow and the head form. The consequence of this is that the pressure difference between the inflow and the high pressure zone is too low for an a priori assumption of sonic flow at the inlet. Fluid/S...
This paper discusses the problem of structural optimization of product families subjected to mult... more This paper discusses the problem of structural optimization of product families subjected to multiple load cases, evaluated by computationally costly finite element analysis. Product families generally have a complex composition of shared components that makes individual product optimization difficult as the relation between the shared variables is not always intuitive. More optimal is to treat the problem as a product family optimization problem. For product families subjected to multiple and computationally costly crash loads, however, the optimization problem takes too long time to solve with traditional methods. Therefore, a new optimization algorithm is presented that decomposes the family problem into sub-problems and iteratively reduces the number of sub-problems, decouple and solve them.
Journal of Materials Processing Technology, 2008
Tube hydroforming is gaining increasing interest from the metal forming industry. Complicated par... more Tube hydroforming is gaining increasing interest from the metal forming industry. Complicated parts with a high level of structural component integration, e.g. engine cradles, subframes and exhaust systems, can be manufactured at a low cost with excellent repeatability. By using finite element (FE) simulations, there is a possibility to reduce the cost of expensive prototypes and reduce the trial and
Structural and Multidisciplinary Optimization
It is important to consider variations in material parameters in the design of automotive structu... more It is important to consider variations in material parameters in the design of automotive structures in order to obtain a robust and reliable design. However, expensive tests are required to gain complete knowledge of the material behavior and its associated variation. Consequently, due to time and cost constraints, simplified material scatter modeling techniques based on scatter data of typical material properties provided by the material suppliers are used at early design stages in simulation-based robustness studies. The aim of this paper is to study the accuracy of the simplified scatter modeling methods in representing the real material variation. The simplified scatter modeling methods are evaluated by comparing the material scatter obtained by them to the scatter obtained by complete tensile tests, which are obtained after detailed timeconsuming experimental investigations. Furthermore, an accuracy assessment is carried out based on selected responses from an axially-crushed, square tube made from DP600 steel.
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Papers by Larsgunnar Nilsson