Huddinge, Sweden
Huddinge, Sweden

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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.


Borvik T.,Norwegian University of Science and Technology | Borvik T.,Norwegian Defence Estates Agency | Olovsson L.,IMPETUS Afea AB | Hanssen A.G.,Norwegian University of Science and Technology | And 4 more authors.
Journal of the Mechanics and Physics of Solids | Year: 2011

The structural response of a stainless steel plate subjected to the combined blast and sand impact loading from a buried charge has been investigated using a fully coupled approach in which a discrete particle method is used to determine the load due to the high explosive detonation products, the air shock and the sand, and a finite element method predicts the plate deflection. The discrete particle method is based on rigid, spherical particles that transfer forces between each other during collisions. This method, which is based on a Lagrangian formulation, has several advantages over coupled LagrangianEulerian approaches as both advection errors and severe contact problems are avoided. The method has been validated against experimental tests where spherical 150 g C-4 charges were detonated at various stand-off distances from square, edge-clamped 3.4 mm thick AL-6XN stainless steel plates. The experiments were carried out for a bare charge, a charge enclosed in dry sand and a charge enclosed in fully saturated wet sand. The particle-based method is able to describe the physical interactions between the explosive reaction products and soil particles leading to a realistic prediction of the sand ejecta speed and momentum. Good quantitative agreement between the experimental and predicted deformation response of the plates is also obtained. © 2011 Elsevier Ltd. All rights reserved.


Wadley H.N.G.,University of Virginia | Borvik T.,Norwegian University of Science and Technology | Borvik T.,Agency for Defense Development | Olovsson L.,IMPETUS Afea AB | And 5 more authors.
Journal of the Mechanics and Physics of Solids | Year: 2013

Light metal sandwich panel structures with cellular cores have attracted interest for multifunctional applications which exploit their high bend strength and impact energy absorption. This concept has been explored here using a model 6061-T6 aluminum alloy system fabricated by friction stir weld joining extruded sandwich panels with a triangular corrugated core. Micro-hardness and miniature tensile coupon testing revealed that friction stir welding reduced the strength and ductility in the welds and a narrow heat affected zone on either side of the weld by approximately 30%. Square, edge clamped sandwich panels and solid plates of equal mass per unit area were subjected to localized impulsive loading by the impact of explosively accelerated, water saturated, sand shells. The hydrodynamic load and impulse applied by the sand were gradually increased by reducing the stand-off distance between the test charge and panel surfaces. The sandwich panels suffered global bending and stretching, and localized core crushing. As the pressure applied by the sand increased, face sheet fracture by a combination of tensile stretching and shear-off occurred first at the two clamped edges of the panels that were parallel with the corrugation and weld direction. The plane of these fractures always lay within the heat affected zone of the longitudinal welds. For the most intensively loaded panels additional cracks occurred at the other clamped boundaries and in the center of the panel. To investigate the dynamic deformation and fracture processes, a particle-based method has been used to simulate the impulsive loading of the panels. This has been combined with a finite element analysis utilizing a modified Johnson-Cook constitutive relation and a Cockcroft-Latham fracture criterion that accounted for local variation in material properties. The fully coupled simulation approach enabled the relationships between the soil-explosive test charge design, panel geometry, spatially varying material properties and the panel's deformation and dynamic failure responses to be explored. This comprehensive study reveals the existence of a strong instability in the loading that results from changes in sand particle reflection during dynamic evolution of the panel's surface topology. Significant fluid-structure interaction effects are also discovered at the sample sides and corners due to changes of the sand reflection angle by the edge clamping system. © 2012 Elsevier Ltd. All rights reserved.


Olovsson L.,IMPETUS Afea AB | Olovsson L.,Norwegian University of Science and Technology | Hanssen A.G.,IMPETUS Afea AS | Hanssen A.G.,Norwegian University of Science and Technology | And 3 more authors.
European Journal of Mechanics, A/Solids | Year: 2010

A new approach to describe blast loading is suggested, herein referred to as the corpuscular approach. The detonation products are modeled as a set of discrete particles following Maxwell's original kinetic molecular theory. For numerical purposes, the number of molecules has to be greatly reduced compared to what one has in real gases. However, the total molecular mass and temperature dependent velocity distribution are the same as in an ideal gas. Pressure loading on structures is then numerically represented by the momentum transfer as particles impact and rebound from the surface of the structure. The suggested approach has significant advantages compared to today's state-of-the-art continuum-based approaches to fully coupled blast-loading computations. The computational time can be significantly reduced, the method is numerically robust and the approach will easily cope with complex geometries in the fluid-structure interface. © 2009 Elsevier Masson SAS. All rights reserved.


Hanssen A.G.,Norwegian University of Science and Technology | Hanssen A.G.,IMPETUS Afea AS | Olovsson L.,Norwegian University of Science and Technology | Olovsson L.,IMPETUS Afea AB | And 3 more authors.
European Journal of Mechanics, A/Solids | Year: 2010

A new resultant-based point-connector model has been developed for use with large-scale finite element crash simulations for non-linear explicit finite element analysis. The nature of the model has been based on the observed physical failure behaviour of a self-piercing rivet connecting two aluminium sheets. The model is able to describe the complete force-deformation behaviour of the SPR connection from initial loading until failure. The paper gives an overview of the analytical background of the model and shows how the model parameters can be identified from experiments using a reverse engineering approach. © 2010 Elsevier Masson SAS. All rights reserved.


Borvik T.,Norwegian University of Science and Technology | Borvik T.,Norwegian Defence Estates Agency | Olovsson L.,Impetus Afea AB | Dey S.,Norwegian Defence Estates Agency
Proceedings - 27th International Symposium on Ballistics, BALLISTICS 2013 | Year: 2013

This paper presents some preliminary results from an ongoing experimental and numerical study on the penetration of granular materials by small-arms bullets. In the present study, 0-2 mm wet and dry sand targets were impacted by 7.62 mm AP bullets. In all tests a rifle was used to fire the bullet, while the sand was randomly packed in a steel tube, and the initial velocity and the depth of penetration were measured. In the numerical simulations, a discrete particle-based approach was used to model the behaviour of the sand during impact. The method works with discrete, rigid, spherical particles that transfer forces between each other through contact and collisions, allowing for a simple treatment of the interaction between the sand particles and the bullet which is represented by finite elements. As will be shown, the agreement between the experimental results and the numerical predictions is good.


Borvik T.,Norwegian University of Science and Technology | Borvik T.,Norwegian Defence Estates Agency | Dey S.,Norwegian Defence Estates Agency | Olovsson L.,IMPETUS Afea AB
International Journal of Impact Engineering | Year: 2015

This paper presents an experimental and numerical study on the penetration of granular materials by small-arms bullets. In the experimental tests, five different types of granular material (0-2 mm wet sand, 0-2 mm dry sand, 2-8 mm gravel, 8-16 mm crushed stone and 16-22 mm crushed rock) were impacted by four different types of small-arms bullets (7.62 mm Ball with a soft lead core, 7.62 mm AP with a hard steel core, 12.7 mm Ball with a soft steel core and 12.7 mm AP with a tungsten carbide core). The tests were carried out using different rifles to fire the projectiles, while the granular materials were randomly packed in a 320 mm diameter specially-designed steel tube. In all tests, the initial projectile velocity and the depth of penetration in the granular material were measured for each bullet type. In the numerical simulations, a discrete particle-based approach was used to model the behaviour of sand during bullet impact. The method works with discrete particles that transfer forces between each other through contact and elastic collisions, allowing for a simple and robust treatment of the interaction between the sand particles and the bullet which is represented by finite elements. An important observation from this study is that the penetration depth is strongly influenced by deviation of the bullet from its original trajectory. Good agreement between the available experimental results and the numerical predictions is also in general obtained. © 2014 Elsevier Ltd. All rights reserved.

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