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Flekkefjord, Norway

Hoang N.-H.,Norwegian University of Science and Technology | Langseth M.,Norwegian University of Science and Technology | Porcaro R.,Norwegian University of Science and Technology | Porcaro R.,Sintef | And 2 more authors.
European Journal of Mechanics, A/Solids | Year: 2011

The joining of two aluminium plates with an aluminium self-piercing rivet, as discussed by Hoang et al. (2010), showed that heating to soften the plates to be joined might be used to avoid plastic compression or fracture in the rivet. In the present paper, the mechanical behaviour of self-piercing riveted connections using an aluminium rivet was investigated. Two U-shaped specimens in alloy AA6063-W, obtained by a solution heat treatment of the alloy in temper T4, were joined using an aluminium self-pierce rivet in alloy AA7278-T6. The mechanical behaviour of these connections was tested after 3 and 30 days of natural aging of the riveted specimens. Test results showed that the strength of the aluminium riveted joints tended to stabilize after three days of natural aging. In order to evaluate the process effect (i.e. the effect of the pre-straining of the plates in W temper as the result of the riveting process, and the subsequent natural age-hardening of the plates) on the mechanical properties of the riveted connection, a comprehensive material test programme was carried out. Test results revealed that there is an interaction between the pre-straining and natural aging which lowers the material properties in terms of the flow stress compared to the 'virgin' material, i.e. the curve obtained after heat treatment and aging only. Then, the process effect on the mechanical behaviour of the riveted connections was investigated more closely by using a 3D-model generated in LS-DYNA. The combined effect of the pre-straining and natural aging was accounted for in the numerical analyses by means of a user-defined constitutive model. Numerical analyses revealed that it is necessary to consider the combined effect of plastic deformation and aging in order to predict the mechanical behaviour with a reasonable accuracy. © 2011 Elsevier Masson SAS. All rights reserved. Source

Holloman R.L.,University of Virginia | Deshpande V.,University of Cambridge | Hanssen A.G.,Impetus Afea AS | Fleming K.M.,University of Virginia | And 2 more authors.
Journal of Mechanics of Materials and Structures | Year: 2013

We explore a novel cellular topology structure based upon assemblies of square cross section tubes oriented in a cross-ply 2D and orthogonal 3D arrangements that can be tailored to support different combinations of through thickness and in-plane loads. A simple dip brazing approach is used to fabricate these structures from assemblies of extruded 6061-T6 aluminum alloy tubes and the through thickness compression of a variety of structures is investigated experimentally and with finite element modeling. We find that the 3D orthogonal structures have an approximately linear dependence of modulus upon relative density. However the strength has a power law dependence upon density with an exponent of approximately 5/3. These cellular structures exhibit almost ideal plastic energy absorption at pressures that can be selected by adjustment of the vertical and in-plane tube wall thicknesses. A finite element model with a nonlinear hardening constitutive law is used to explore the buckling modes of the structure, and to investigate the relationship between cell topology, relative density, tube wall material properties and the cellular structures resistance to compression. Source

Olovsson L.,IMPETUS Afea AB | Limido J.,IMPETUS Afea SAS | Lacome J.-L.,IMPETUS Afea SAS | Hanssen A.G.,Impetus Afea AS | Petit J.,CEA DAM Gramat
EPJ Web of Conferences | Year: 2015

The modeling of fragmentation has historically been linked to the weapons industry where the main goal is to optimize a bomb or to design effective blast shields. Numerical modeling of fragmentation from dynamic loading has traditionally been modeled by legacy finite element solvers that rely on element erosion to model material failure. However this method results in the removal of too much material. This is not realistic as retaining the mass of the structure is critical to modeling the event correctly. We propose a new approach implemented in the IMPETUS AFEA SOLVER® based on the following: New High Order Finite Elements that can easily deal with very large deformations; Stochastic distribution of initial damage that allows for a non homogeneous distribution of fragments; and a Node Splitting Algorithm that allows for material fracture without element erosion that is mesh independent. The approach is evaluated for various materials and scenarios:-Titanium ring electromagnetic compression; Hard steel Taylor bar impact, Fused silica Taylor bar impact, Steel cylinder explosion, The results obtained from the simulations are representative of the failure mechanisms observed experimentally. The main benefit of this approach is good energy conservation (no loss of mass) and numerical robustness even in complex situations. © 2015 Owned by the authors, published by EDP Sciences. Source

Fyllingen O.,Bergen University College | Hopperstad O.S.,Norwegian University of Science and Technology | Hanssen A.G.,Norwegian University of Science and Technology | Hanssen A.G.,Impetus Afea AS | Langseth M.,Norwegian University of Science and Technology
Thin-Walled Structures | Year: 2010

In the present study, the influence of element type and formulation is investigated in finite element analyses of aluminium profiles subjected to axial crushing. It is shown that solid element-based simulations give predictions in better agreement with experiments both with respect to energy dissipation and folding pattern, while plane stress shell elements markedly underestimate the energy dissipation. It is further found that shell elements with thickness stretch give dissipated energies in better agreement with those obtained in simulations with solid elements. © 2009 Elsevier Ltd. All rights reserved. Source

Salaon N.,GexCon AS | Hanssen A.G.,Impetus Afea AS | Nilsen P.E.,Statoil
Chemical Engineering Transactions | Year: 2016

This paper proposes an advanced and innovative methodology for risk-based structural response assessment against accidental explosions. Focus is shifted from dimensioning load to barrier integrity. A full spatial mapping of blast overpressure transients obtained with Computational Fluid Dynamics (CFD) modelling is used in combination with a Non-Linear Finite Element model (NLFEA). The GexCon-Impetus methodology is so-called advanced due to the innovative extensive one-To-one CFD-NLFEA job solution scheme used over several explosion runs. Using a detailed explosion loads mapping for the response evaluations provides a comprehensive probabilistic description of the response characteristics, easy to combine with risk acceptance criteria and performance requirements. The 3D codes involved are FLACS (CFD) and IMPETUS Afea solver (NLFEA). The response of an offshore fire partition wall is specifically studied against dynamic explosion loads. Detailed modeling of the wall is made in IMPETUS Afea solver. Systematic direct coupling between 90 FLACS risk-based explosion simulations and 90 IMPETUS Afea dynamic response calculations is used. The safety barrier performance is quantified using adequate wall response parameters reported for every explosions. The innovative outcome is a probabilistic picture of the response parameters exceedance. The barrier ability to perform the related safety function(s) is efficiently documented. Of utmost importance, mechanisms that cause possible lack of integrity are highlighted. The results are compared with existing offshore approaches based on the Dimensioning Accidental Load (DAL) concept. A uniform triangular loading and a realistic dimensioning explosion are used. Promoting more consideration of adequate response assessment as part of the safety studies, the paper shows how the advanced method pinpoints limitations of conventional approaches. For the risk owner, it improves the comprehension and implications upon the relation between explosion loads and their consequences on structures carrying critical safety functions. Several benefits result from the GexCon-Impetus approach among which: A more accurate streamlined workflow, an improved understanding of the safety barrier behavior, perception of safety margins, justifications for design optimization, cost & weight savings. © Copyright 2016, AIDIC Servizi S.r.l. Source

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