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Pressure-impulse diagram of a beam developing non-linear membrane action under blast loading Hamra, Lotfi ; Demonceau, Jean-François ; Denoël, Vincent in International Journal of Impact Engineering (2015), 86 The p–I diagram of a frame beam subjected to blast loading is established, including the elastic lateral restraint and inertia offered by the rest of the structure, the development of nonlinear membrane ... [more ▼] The p–I diagram of a frame beam subjected to blast loading is established, including the elastic lateral restraint and inertia offered by the rest of the structure, the development of nonlinear membrane action and also, the bending-tension (M−N) interaction that develops in the plastic hinges. The analytical procedures to compute the asymptotes in the p–I diagram as well as a parametric study on the p–I diagram are provided. A dimensional analysis of the problem reveals that, under the considered assumptions, four dimensionless parameters mainly influence the required ductility of the beam. Two of them are related to the behavior of the indirectly affected part (the lateral restraint and mass). Another one is related to the mechanical properties of the investigated beam (i.e. the ratio of the bending to axial resistance). The last parameter incorporates scales of the geometry and of the deformed configuration at the onset of the plastic mechanism. [less ▲] Detailed reference viewed: 113 (38 ULg)Enhanced ALE Data Transfer Strategy for Explicit and Implicit Thermomechanical Simulations of High-Speed Processes Boman, Romain ; Ponthot, Jean-Philippe in International Journal of Impact Engineering (2013), 53 The Arbitrary Lagrangian Eulerian (ALE) formalism, which allows the computational grid to move regardless of thematerial deformation, is a convenient way to avoid distortedmeshes in finite element ... [more ▼] The Arbitrary Lagrangian Eulerian (ALE) formalism, which allows the computational grid to move regardless of thematerial deformation, is a convenient way to avoid distortedmeshes in finite element simulations. One crucial step of the ALE algorithm is the data transfer between the Lagrangian and the Eulerian meshes. In this paper, an enhanced transfer method is presented. It can handle complex finite elements which are integrated with more than one Gauss point. This method can thus be used either with an explicit or with an implicit time integration scheme. Choosing the adequate order of accuracy and the most appropriate number of physical fields to be transferred is always a compromise between the speed and the precision of the model. For example, some variables may be sometimes ignored during the transfer in order to decrease the CPU time. Therefore, the most effective way to use such an algorithm is demonstrated in this work by revisiting a classical ALE benchmark, the Taylor impact. An implicit thermomechanical ALE simulation of a high-speed tensile test is also presented and is compared to experimental results from the literature. [less ▲] Detailed reference viewed: 45 (19 ULg)Comparative study of numerical explicit schemes for impact problems ; Ponthot, Jean-Philippe ; Noels, Ludovic in International Journal of Impact Engineering (2008), 35(12), 1688-1694 Explicit numerical schemes are used to integrate in time finite element discretization methods. Unfortunately, these numerical approaches can induce high-frequency numerical oscillations into the solution ... [more ▼] Explicit numerical schemes are used to integrate in time finite element discretization methods. Unfortunately, these numerical approaches can induce high-frequency numerical oscillations into the solution. To eliminate or to reduce these oscillations, numerical dissipation can be introduced. The paper deals with the comparison of three different explicit schemes: the central difference scheme which is a nondissipative method, the Hulbert Chung dissipative explicit scheme and the Tchamwa-Wielgosz dissipative scheme. Particular attention is paid to the study of these algorithms’ behavior in problems involving high-velocity impacts like Taylor anvil impact and bullet-target interactions. It has been shown that Tchamwa-Wielgosz scheme is efficient in filtering the high-frequency oscillations and is more dissipative than Hulbert Chung explicit scheme. Although its convergence rate is only first order, the loss of accuracy remains limited to acceptable values. [less ▲] Detailed reference viewed: 118 (15 ULg)Simulation of crashworthiness problems with improved contact algorithms for implicit time integration Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe in International Journal of Impact Engineering (2006), 32(5), 799-825 When studying crashworthiness problems, contact simulation can be the source of a number of problems. A first one is the discontinuities in the normal evolution for a boundary discretized by finite ... [more ▼] When studying crashworthiness problems, contact simulation can be the source of a number of problems. A first one is the discontinuities in the normal evolution for a boundary discretized by finite elements. Another problem is the treatment of the contact forces that can introduce numerical energy in the system. In this paper, we propose to combine a method of discontinuity smoothing with the energy-momentum consistent scheme that recently appeared in the literature. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲] Detailed reference viewed: 48 (6 ULg)Simulation of complex impact problems with implicit time algorithms: Application to a turbo-engine blade loss problem Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe in International Journal of Impact Engineering (2005), 32(1-4), 358386 Recent developments, in non-linear structural dynamics, have led to a new kind of implicit algorithms: the energy-momentum conserving algorithm (EMCA) and the energy-dissipative, momentum-conserving ... [more ▼] Recent developments, in non-linear structural dynamics, have led to a new kind of implicit algorithms: the energy-momentum conserving algorithm (EMCA) and the energy-dissipative, momentum-conserving algorithm. Contrarily to commonly used algorithms, such as the explicit central difference or the alpha-generalized method, the stability of those algorithms is always ensured in the non-linear range. Thanks to this unconditional stability the only requirement on the time step size is that it must be small enough to capture the physics. This requirement is less restrictive than a conditional stability. In previous works, we have developed a new formulation of the internal forces for a hypoelastic model, that leads to an EMCA. In this paper, we will extend this formulation to an energy-dissipative, momentum-conserving algorithm. We will prove with an academic example, that our algorithm is more accurate than the alpha-generalized method in the non-linear range. Then we will simulate a blade loss problem to demonstrate the efficiency of our developments on complex dynamics simulations. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲] Detailed reference viewed: 46 (3 ULg)Combined implicit/explicit algorithms for crashworthiness analysis Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe in International Journal of Impact Engineering (2004), 30(8-9, SEP-OCT), 1161-1177 In order to simulate an industrial process, an explicit method, which is conditionally stable, is the most adapted while the non-linearities evolve rapidly (impact phase, stamping process, etc.). But when ... [more ▼] In order to simulate an industrial process, an explicit method, which is conditionally stable, is the most adapted while the non-linearities evolve rapidly (impact phase, stamping process, etc.). But when the dynamics becomes quasi-linear (post-impact analysis, springback simulation, etc.), an implicit method, which is iterative, presents the advantage of unconditional stability. The optimal solution is then to have both implicit and explicit methods readily available in the same code and to be able to switch automatically from one to the other. Criteria that decide to switch from one method to another, depending on the current dynamics, have been developed. Implicit restarting conditions are also proposed that annihilate numerical oscillations resulting from an explicit calculation. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲] Detailed reference viewed: 49 (7 ULg) |
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