Browsing by Author "Campbell, James C."
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Item Open Access Application of the finite element method to predict the crashworthy response of a metallic helicopter under floor structure onto water.(Elsevier Science B.V., Amsterdam., 2008-05-01T00:00:00Z) Hughes, Kevin; Campbell, James C.; Vignjevic, RadeHelicopters are seen by the petroleum industry as the only viable way of transportation between on and offshore platforms. At present, there exists no certification requirement to ensure a high level of survivability in the event of a water impact. Within the literature, there exists a body of information related to the post crash analysis of accident data, which supports the finding that a conventional metallic under floor design performs poorly during a water impact, in relation to the transmission of water pressure and the absorption of energy. In order to characterise this behaviour, this paper concerns the crashworthiness of helicopters on water for an impact speed of 8 m s−1, for a simple box-beam construction that is common to metallic helicopters. A complete section-by-section analysis of a component floor will be presented, which has been compared both quantatively and qualitatively with the results provided by the finite element code, LS-DYNA3D. Comparisons will be made to collapsed frame height, as well as to detailed measurements for skin deflection. The main areas of good and poor agreement are discussed and conclusions drawn on the validity of the simulations, with a view for developing a practical methodology for fluid–structure interactions. This paper discusses the recommendations for design changes that could potential improve the level of crashworthiness currently offered, through the careful redesign of frames and joints, in order to allow for progressive collapse and sustained energy absorption. This paper concludes with a recommendation that a next generation design must incorporate a passive dual role capability that can cater for both hard and soft surface impacts, by being able to degrade its localised strength depending upon the type of surface encountered.Item Open Access Derivation of SPH equations in a moving referential coordinate system(Elsevier Science B.V., Amsterdam., 2009-06-01T00:00:00Z) Vignjevic, Rade; Campbell, James C.; Jaric, J.; Powell, S.The conventional SPH method uses kernel interpolation to derive the spatial semi-discretisation of the governing equations. These equations, derived using a straight application of the kernel interpolation method, are not used in practice. Instead the equations, commonly used in SPH codes, are heuristically modified to enforce symmetry and local conservation properties. This paper revisits the process of deriving these semi-discrete SPH equations. It is shown that by using the assumption of a moving referential coordinate system and moving control volume, instead of the fixed referential coordinate system and fixed control volume used in the conventional SPH method, a set of new semi- discrete equations can be rigorously derived. The new forms of semi-discrete equations are similar to the SPH equations used in practice. It is shown through numerical examples that the new rigorously derived equations give similar results to those obtained using the conventional SPH equations.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 Experimental observations of an 8 m/s drop test of a metallic helicopter underfloor structure onto water: part 2.(Professional Engineering Publishing, 2007-01-01T00:00:00Z) Hughes, Kevin; Vignjevic, Rade; Campbell, James C.This is the second part of a two-part paper that describes the experimental observations for two similar sections of floor that were dropped onto both hard and water surfaces at 8 m/s, as part of one experimental campaign. The current paper provides an assessment of a simple box-beam under floor structure typically found in metallic helicopters and provides an overview of the failure modes and the collapse mechanism observed when dropped onto water at 8 m/s, as well as providing quantitative data for the skin deflections observed. The results demonstrate that the lack of frame and intersection joint collapse is a common feature, which is caused by the high failure strength of the existing construction, together with the inability of the skin to generate membrane loads that are sufficiently large to trigger progressive collapse within the structure. It is therefore recommended to reduce the collapse force of the structure through the use of geometry, material type, and inclusion of triggers. However, the caveat with this approach is that if the failure strength is optimized for a water impact, a poor crashworthy response may occur during a hard surface impact. The current paper discusses three main limitations with the design, which are heavily interrelated, as improvements in frame and joint collapse cannot be achieved without considering developing the ductile behaviour of the skin. However, maintaining skin integrity will be critical to maintain the floatation capabilities of the helicopter. The current paper recommends that a next generation design should encompass a passive dual role capability for both hard and soft surface impacts, by being able to degrade the localized strength depending upon the type of surface encountered. This will significantly improve the crashworthy response of a metallic under floor structure and have a significant impact on improving occupant survivability for an impact on water.Item Open Access Experimental observations of an 8ms-1 drop test of a metallic helicopter underfloor structure onto a hard surface: part 1(Professional Engineering Publishing, 2007-06-12T00:00:00Z) Hughes, Kevin; Vignjevic, Rade; Campbell, James C.Abstract: This is the first part of a two-part paper that describes the experimental observations for two similar sections of floor that were dropped onto both hard and water surfaces at 8 m/s, as a part of one experimental campaign. The current paper provides an assessment of a simple box-beam underfloor structure typically found in metallic helicopters and provides an overview of the failure modes and the collapse mechanism observed when dropped onto a hard surface. All findings are supported by quantitative measurements and extensive photographic evidence. The current paper identifies two limitations with the existing design, which are based upon the observations of the failure modes for different frame types and the performance of the intersection joints. In order to increase the level of crashworthiness currently offered, significant frame and joint redesign is required in order to provide a more progressive collapse. The simple buckling modes currently observed should be avoided, as the existing stroke is not fully utilized in the event of a crash, resulting in an inefficient structure. The current paper also discusses the sensitivity to impact angle, as slight variations from a normal impact may result in a detrimental response.Item Open Access Helicopter crashworthiness: a chronological review of research related to water impact from 1982 to 2006(American Helicopter Society Inc, 2008-06-02T00:00:00Z) Hughes, Kevin; Campbell, James C.This paper discusses in detail the contributions made in the field of water impact from 1982 to 2006 and provides a summaryof the major theoretical, experimental, and numerical accomplishments, up to and including the latest present-day Europeanprograms on helicopter water crashworthiness. A summary of the major findings is presented, and their importance to thedirection of water crashworthiness development is discussed, together with recommendations for future research.Item Open Access Modeling shock waves in orthotropic elastic materials(American Institute of Physics, 2008-08-01T00:00:00Z) Vignjevic, Rade; Campbell, James C.; Bourne, Neil K.; Djordjevic, NenadA constitutive relationship for modeling of shock wave propagation in orthotropic materials is proposed for nonlinear explicit transient large deformation computer codes (hydrocodes). A procedure for separation of material volumetric compression (compressibility effects equation of state) from deviatoric strain effects is formulated, which allows for the consistent calculation of stresses in the elastic regime as well as in the presence of shock waves. According to this procedure the pressure is defined as the state of stress that results in only volumetric deformation, and consequently is a diagonal second order tensor. As reported by Anderson et al. [Comput. Mech.15, 201 (1994)], the shock response of an orthotropic material cannot be accurately predicted using the conventional decomposition of the stress tensor into isotropic and deviatoric parts. This paper presents two different stress decompositions based on the assumption that the stress tensor is split into two components: one component is due to volumetric strain and the other is due to deviatoric strain. Both decompositions are rigorously derived. In order to test their ability to describe shock propagation in orthotropic materials, both algorithms were implemented in a hydrocode and their predictions were compared to experimental plate impact data. The material considered was a carbon fiber reinforced epoxy material, which was tested in both the through-thickness and longitudinal directions. The psi decomposition showed good agreement with the physical behavior of the considered material, while the zdeta decomposition significantly overestimated the longitudinal stresses.Item Open Access Modelling of dynamic damage and failure in aluminium alloys(Elsevier Science B.V., Amsterdam., 2012-11-30T00:00:00Z) Vignjevic, Rade; Djordjevic, Nenad; Campbell, James C.; Panov, ViliA physically based damage and failure model, applicable to orthotropic metals is proposed in this paper. To account for the physical mechanisms of failure, the concept of thermally activated damage initially proposed by Klepaczko [1], has been adopted as the basis for the model. This assumption makes the proposed damage/failure model compatible with the Mechanical Threshold Strength (MTS) model [2-6], which was used within the overall constitutive model to describe material behaviour in the plastic regime. A shock equation of state [7] was coupled with the rest of the constitutive model to allow for modelling of shock wave propagation in the material. The new model was implemented in DYNA3D [8] and coupled with our in-house non-linear transient SPH code, MCM (Meshless Continuum Mechanics). Parameters for the new constitutive model, i.e. parameters for the plasticity model and the damage model, were derived on the basis of the uniaxial tensile tests and Taylor anvil tests. The subject of investigation is a polycrystalline aluminium alloy AA7010, whose orthotropy is a consequence of meso-scale phase distribution, or grain morphology. Tensile tests were performed for the range of temperatures between and , and strain rates between and . In order to validate the new damage model, a numerical simulation of Taylor anvil tests has been performed for AA7010, using a single stage gas gun at velocity of . The numerical analysis clearly demonstrates the ability of this new model to predict experimentally observed damage and failure.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 Modelling of liquid metal flow and oxide film defects in filling of aluminium alloy castings(2012-12-31T00:00:00Z) Dai, Xiaojun J.; Jolly, Mark R.; Yang, X; Campbell, James C.The liquid metal flow behaviours in different runner system designs have important effects on the mechanical strength of aluminium alloy castings. In this paper, a new model has been developed which is a two-dimensional program using a finite difference technique and the Marker and Cell (MAC) method to simulate the flow of liquid metal during filling a mould. In the program the Eulerian method has been used for the liquid metal flow, while the Oxide Film Entrainment Tracking Algorithm (OFET) method (a Lagrangian method) has been used to simulate the movement of the oxide film on the liquid metal surface or in the liquid metal flow. Several examples have been simulated and tested and the relevant results were obtained. These results were compared with measured bending strengths. It was found that the completed program was capable of simulating effectively the filling processes of different runner systems. The simulation results are consistent with the experiment. In addition, the program is capable of providing clearer images for predicting the distribution of the oxide film defects generated during filling a mould.Item Open Access Non-linear idealisation error analysis of a metallic stiffened panel loaded in compression(Elsevier Science B.V., Amsterdam., 2012-05-31T00:00:00Z) Campbell, James C.; Hetey, Laszlo; Vignjevic, RadeThe SAFESA procedure is an idealisation error control process developed for linear static finite element (FE) analysis. This paper investigates the application of this process to non-linear FE in order to provide an equivalent methodology valid for non-linear problems. The post-bucked collapse of a stiffened panel in compression is used as the case study for this investigation. The main part of the paper presents the critical analysis of important modelling assumptions, including the material model, the panel to stiffener contact, boundary conditions and geometrical imperfections. Several potential idealisation error sources are identified using the process and then investigated using the non-linear FE code ABAQUS. The outcome of the analysis is an improved FE model and a quantification of the idealisation error, showing that the idealisation error control process can be applied to non-linear analysisItem Open Access Numerical simulation of high velocity impacts on thin metallic targets I and II(2004-12-18T00:00:00Z) Vignjevic, Rade; Campbell, James C.; Lepage, SéverineSpacecraft encounter various impact phenomena in space, among which orbital debris impacts are of most concern. These impacts occur at a wide range of velocities. Impact velocities from a few hundreds m/s to one km/s are common in geostationary orbit and even occur in low Earth orbit. However, these high velocity impacts are not fully characterised. It’s required to study the shielding performance in order to assess the spacecraft survivability in the event of high velocity impacts. The paper is divided into two parts. Overall it investigates the capability of hydrocodes to simulate high velocity impacts. Particular interest is given to the post-penetration debris cloud characterisation and the material failure mode identification. Three different methods were used to simulate the impact of an aluminium sphere on a thin aluminium plate. The first part, considers analyses performed using a finite element model with element erosion and a discrete element method where the problem is modelled with discrete finite elements with nodes tied with breakable linkages. The second part of the paper considers the same problems with the Smoothed Particle Hydrodynamics (SPH) method using the MCM solver developed at Cranfield University. All three methods showed good agreement in terms of target damage with the available experimental results. However, their performances are different in terms of debris cloud and failure mode characterisation. As a large number of elements are deleted, the element erosion method shows problems in the petaling failure mode representation and doesn’t allow the post-penetration debris cloud to be characterised. In order to be more reliable, the SPH method needs improvements, in particular to avoid tensile instability. The discrete element method allows good representation and identification of the failure modes even if some improvements in the definition of the node linkage failure criterion are requiItem 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 Simulating structural response to water impact(Elsevier Science B.V., Amsterdam., 2012-11-30T00:00:00Z) Campbell, James C.; Vignjevic, RadeStructural response to water impact is important for several areas, including the aerospace and marine industries. Aircraft must be designed to cope with ditching and offshore structures are subject to extreme wave impact and green water loading. The goal is a reliable technique for predicting the structural response to extreme water loading. This is a complex problem involving the interaction of non-linear fluid behaviour (breaking waves, fluid impact) with non-linear structural behaviour (large deformations, contact, material plasticity and damage). This paper gives an overview of the coupled FE/SPH approach for modelling water impact on structures and discusses specific issues related to the analysis of floating structures. The capabilities of the method are illustrated first through comparison with published numerical results for simple problems involving the equilibrium of rigid floats and an initially submerged cylindrical float. Then by comparison with experimental data for the collapse of a metallic helicopter floor structure due to impact with water. Finally the response of a moored buoy to an extreme wave is modelled. The sensitivity of the model to spatial resolution is investigated for the rising cylinder and helicopter floor cases.