Browsing by Author "De Vuyst, Tom"
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Item Open Access Evaluation of the SPH method for the modelling of spall in anisotropic alloys(2005-06-27T00:00:00Z) De Vuyst, Tom; Vignjevic, Rade; Bourne, Neil K.; Campbell, James C.Spall caused by hypervelocity impacts at the lower range of velocities could result in significant damage to spacecraft. A number of polycrystalline alloys, used in spacecraft manufacturing, exhibit a pronounced anisotropy in their mechanical properties. The aluminium alloy AA 7010, whose orthotropy is a consequence of the meso-scale phase distribution or grain morphology, has been chosen for this investigation. The material failure observed in plate impact was simulated using an explicit finite element code and a smoothed particle hydrodynamics (SPH) code. A number of spall models where used, and the Hugoniot Elastic Limit (HEL) and spall strength have been studied as a function of orientation, and compared to experimental results.Item Open Access Hydrocode modelling of water impact(2003-03) De Vuyst, Tom; Vignjevic, RadeThis thesis addresses the problem of hydrocode modelling of water impact. Two facets that are of importance when numerically modelling the impact of metallic structures on water are metal anisotropy and water behaviour during impact. In order to be able to take account of these effects in a hydrocode simulation an SPH solver has been incorporated into LLNL-DYNA3D. The treatment of contact in meshless methods has been addressed through the development of a contact algorithm which does not require the construction of surfaces. The interaction of finite elements and SPH particles is accounted for by using a novel approach in treating the finite element nodes as particles in the contact treatment. The same contact algorithm developed for the treatment of contact in the SPH method has been used. In order to take account of metal anisotropy a material model that takes account of anisotropy in the elastic and plastic regimes, strain-rate dependency and non-linear behaviour at high pressures including spall failure was developed. The developed simulation tool is validated against experimental data for the case of water impact of rigid cylinders on water. Further validation is achieved by demonstrating that the simulation tool can be used to analyse the crash behaviour of subfloor designs on water. This was achieved by simulating the impact on water of a structure representative of an aircraft subfloor. The effect of material anisotropy, skin thickness and skin failure on the structural response was demonstrated. A first step in extending the coupled FE-SPH modelling beyond fluid-structure interaction problems has been the development and validation of an explicit time integration ID Lagrangian kernel SPH code which in combination with an algorithm to track crack propagation would make the simulation of dynamic brittle fracture problems possible.Item Open Access Modelling of impact on a fuel tank using smoothed particle hydrodynamics(2005-06-27T00:00:00Z) Vignjevic, Rade; De Vuyst, Tom; Campbell, James C.; Bourne, Neil K.This paper describes a modelling approach for the simulation of hypervelocity impact on fuel tanks using the Smoothed Particle Hydrodynamics (SPH) method. To determine a suitable particle density, three two-dimensional axi-symmetric models were analysed. Then three-dimensional simulations with cylindrical and cubic penetrators were performed. For each analysis the transient pressure values at locations corresponding to experimental transducer locations were recorded. The pressure time histories are shown for the axi-symmetric and 3D models. The simulation results are compared with the experimental results. The purpose of the research was to demonstrate the capability and potential of SPH for simulating this type of problem.Item Open Access A numerical study on the influence of internal corrugated reinforcements on the biaxial bending collapse of thin-walled beams(Elsevier, 2019-07-25) Vignjevic, Rade; Liang, Ce; Hughes, Kevin; Brown, Jason C.; De Vuyst, Tom; Djordjevic, Nenad; Campbell, James C.The Heat Treatment Forming and in-die Quench (HFQ) process allows for manufacturing of more complex geometries from Aluminium sheets than ever before, which can be exploited in lightweight automotive and aerospace structures. One possible application is manufacturing thin walled beams with corrugated internal reinforcements for complex geometries. This work considers different internal reinforcements (C-section and corrugated) to improve the energy absorption properties of thin walled rectangular beams under uniaxial and biaxial deep bending collapse, for loading angles ranging from 0 to 90 deg, in 15° increments. Using LS-DYNA simulations experimentally validated through unreinforced metallic tubes under quasi-static bending collapse, the finite element results demonstrate the stabilising effect of the reinforcements and an increase in the buckling strength of the cross section. Corrugated reinforcements showed a greater potential for increasing specific energy absorption (SEA), which was supported by investigating key geometric parameters, including corrugation angle, depth and number. This favourable response is due to an increased amount of material undergoing plastic deformation, which consequently improves performance of the beam undergoing post buckling and deep collapse. This concept is applicable to vehicle and aircraft passive safety, with the requirement that the considered geometries are manufacturable from Aluminium Alloys sheet only, using the HFQ processItem Open Access Simulation of hard projectile impact on friction stir welded plate(Cranfield University, 2011-12) Wang, Wei; De Vuyst, TomA numerical simulation is conducted using LS-DYNA to simulate hard projectile impact on a friction stir welded (FSW) plate. As the hard projectile has a wide range of velocity, mass and shape, when referring to AMC 25.963(e) of CS-25, ―Fuel Tank Access Cover‖, the hard projectile can be defined as 9.5 mm cubic-shaped steel engine debris with an initial impact velocity of 213.4 m/s (700 ft/s). This preliminary study was to evaluate whether the fuel tank adjacent skin panel joined by FSW would pass the regulation. First, the geometry and Johnson-Cook material model of the FSW joint were developed based on previous experimental research and validated by comparison with the tensile test on the FSW specimen. Then the impact on an Aluminium Alloy 2024 (AA 2024) plate without FSW was modelled. The minimum thickness of a homogeneous AA 2024 plate which could withstand the impact from engine debris is 3 mm. Finally the impact on 3 mm thick AA 2024 FSW plate was simulated. The welding induced residual stress was implemented in the plate model. The impact centre was changed from the nugget zone to the thermo-mechanically affected zone, heat-affected zone and base material zone of the FSW joint. Penetration only occurred in the model with impact centre on the nugget zone. Additional simulation indicated that increasing the thickness of the FSW plate to 3.6 mm could prevent the penetration.Item Open Access Theoretical development of the SPH method and application to transient fluid structure interaction problems.(2018-11) Portelli, Daniel; De Vuyst, TomThe smoothed particle hydrodynamic method (SPH) is a meshless method that suffers from several shortcomings. These shortcomings are tensile instability and zero energy modes -which are characterised by unphysical particle clumping- lack of consistency and improper enforcement of essential boundary conditions. The capability of the method also lacks; with most applications limited to either fluid or very simple fluid-structure interactions. This thesis addresses most of the issues that plague SPH as well as extending the capability to more complex fluid-structure interactions. Particle clumping has been reduced by the introduction and rigorous mathematical and code development of a mixed formulation procedure that while is prevalent in finite element, has never been applied to the SPH method. Unlike every other attempt in literature to solve the particle clumping problem, this approach addresses the cause as opposed to treat the symptoms, which gives it mathematical rigour and generality. Furthermore, a moving least squares procedure was applied to the code to smooth pressure by using a first order consistent scheme, this gave an unexpected side effect in the form of velocity differences between simulations that used the procedure and those that did not. This was investigated and conclusions drawn into the nature of why this difference occurred. Extension of the capability of the method occurred by the addition of rotational boundary conditions and modification of the contact algorithm to account for a no-slip boundary condition to achieve successful simulation of complex fluid-structure interaction problems. These problems were three benchmark cases involving the interaction of an elastic body and free surface flow. Validation occurred throughout the development of the code and simulations. Code validation was by comparison to theory, while the results of the beam deflection were compared to LS-Dyna. The benchmark cases were compared to both experimental results and to another paper who modelled the problem using a partitioned finite volume solver. All coding and simulations in this work was done within in the inhouse Meshless continuum mechanics (MCM) code.Item Open Access Total Lagrangian SPH modelling of necking and fracture in electromagnetically driven rings(Springer Science Business Media, 2013-03-31T00:00:00Z) De Vuyst, Tom; Vignjevic, RadeThis paper describes research on the prediction of necking and failure in metals at very high strain rates. The model developed in this paper uses a total Lagrangian SPH formulation with a normalised kernel. The detailed data from electromagnetically driven ring experiments by Zhang and Ravi-Chandar (Int J Fract 142:183-217, 2006) is used to evaluate the accuracy of the model predictions. In order to correctly model fracture in the total Lagrangian SPH formulation a visibility criterion based on a truncated cone has been implemented to remove particles obscured by a failed particle. A Johnson-Cook plasticity model is used in combination with a Lemaitredamage model to describe the plastic deformation and fracture of the rings. The effect of Joule heating due to the current induced in the ring is taken into account in the constitutive model. The acceleration due to the ring currents was implemented in the SPH code as a body force. The results demonstrate that this type of model is capable of predicting the number of fragments as well as the time of fracture. In agreement with experimental data, the model also predicts arrested necks and bending in the fragments.