Browsing by Author "Campbell, James"
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Item Open Access Application of improved Lagrangian techniques for helicopter crashworthiness on water(Cranfield University, 2005-05) Hughes, K.; Campbell, JamesThis thesis concerns the crashworthiness of helicopters onto water and presents a comparison between test and simulation for the impact of a typical helicopter sub floor section onto both hard and water surfaces. The experimental campaign was extended to incorporate a fully instrumented WG30 helicopter drop test onto water, which allowed a comprehensive assessment of the predictive capabilities of the non-linear code LS- DYNA3D to be performed. Validation data was supplied from specific drop tests, which permitted a complete frarne-by-frame analysis to be performed and compared both quantitively and qualitatively with the numerical results. The conclusions from this work enabled a assessment of the validity of the component and full-scale simulations with respect to one another, together with the design changes that could potentially improve the level of crashworthiness currently offered with the current design. Modelling the compressive behaviour of a fluid using a Lagrangian approach is difficult, due to the inherent mesh problems associated with large definitions. Sensitivity studies were performed, which led to the development of a tuned water model that was capable of recreating the impact of various rigid shapes onto water. Alternative techniques to water modelling are also presented in a attempt to minimise the stability problems that arise between fluid and structure boundary, where the definite elements attempt to form a splash. To complete this review of the capabilities of the code, a assessment with respect to capturing joint failure was also performed, through comparison with joint coupon tests. As no methodology concerning the simulation of fluid-structure interaction problems exists within the literature, this thesis addresses this issue by discussing the contributions made to the SAFESA approach (SAFE Structural Analysis), in identifying potential sources of error that are relevant when performing these types of analysis. A discussion of the sources of idealisation, procedural and formulation errors will be performed, along with techniques and recommended practices that have been developed to minimise their affects. The methodology has been extensively tested to be a robust and reliable approach that will greatly assist engineers working in this field. The culmination of this research is the application of the validated simulation tools in developing a potential solution for improving the water crashworthiness response. The concept of maximising skin defection through the purposeful collapse of the interconnecting frames is presented. This would allow the skin to form a continuous curve, as opposed to several inter frame defections. The numerical results verify that this hypothesis could be of benefit in reducing the magnitudes of the accelerations and raises the question of whether next generation designs should concentrate on developing energy absorbing characteristics for each individual cell, or whether a coupled, multiple cell configuration is more preferable.Item Open Access The development and assessment of behavioural markers to support counter-IED training(Elsevier, 2014-12-16) Nixon, Jim; Leggatt, Andrew P.; Campbell, JamesThis article describes the method used to develop and test a checklist of behavioural markers designed to support UK military forces during Counter-Improvised Explosive Device (C-IED) training. IEDs represent a significant threat to UK and allied forces. Effective C-IED procedures and techniques are central to reducing risk to life in this safety critical role. Behavioural markers have been developed to characterise and assess non-technical skills which have been shown to be important in maintaining high performance in other safety critical domains. The aims of this study were two-fold. Firstly to develop a method which could be used to capture and assess operationally relevant behavioural markers for use in C-IED training relating primarily to non-technical skills. Secondly, to test the user acceptance of the behavioural marker checklist during military training activities. Through engagement with military subject matter experts, operationally relevant and observable behaviours seen in C-IED training have been identified and their links to stronger and weaker performance have been established. Using a card-sort technique, the content validity of each of the markers was assessed in addition to their detectability in an operational context. Following this assessment, a selection of the most operationally relevant and detectable behaviours were assimilated into a checklist and this checklist was tested in C-IED training activities. The results of the study show that the method used was effective in generating and assessing the behavioural markers using military subject matter experts. The study also broadly supports the utility and user-acceptance of the use of behavioural markers during training activities. The checklist developed using this methodology will provide those responsible for delivering instruction in C-IED techniques and procedures with a straightforward process for identifying good and poor performance with respect to non-technical skills. In addition it will provide a basis for the provision of focussed feedback to trainees during debrief.Item Open Access Experimental and numerical modeling of high speed ice impact onto rigid target(Cranfield University, 2015-03) Heng, Fangming; Campbell, JamesThe core goal of this research is to develop an ice impact modelling methodology for ice impact on aircraft structures. The main current limitation of ice impact analysis is the ice constitutive model, so this research is focussed on the assessment and improvement of current ice constitutive models. Centre on this aim three aspect works has been done. First, investigating the ice mechanical properties. Through literature review 8 properties of ice have been identified as crucial properties of ice when modelling ice or assessing the ice material model. Secondly, assessing the current material models theoretically and numerically and identify areas where improvements can be made to current ice constitutive models. Five existing ice material models are investigated through theoretical study. Two of them, MAT 13 and MAT 155, are available to use in the LS-Dyna and have been tested through modelling 3 different test problems. Through the investigation of the ice model, MAT 155 is proved to be the optimum ice material model as it reflects the most features (including the compaction feature, bilinear hardening, pressure based failure mode, strain rate dependence) of ice. Through the research of MAT 155, three modified methods of MAT 155 are proposed. Thirdly, developing an implementation of an ice constitutive model as a tool for future assessment of improvements to ice modelling. An LS-Dyna user defined material model (UMAT) based on MAT 155 has been built up and modified by adding the pressure dependence feature. Through the building up and verification of UMAT, two features of MAT 155 were found to perform differently than was described in Carney’s article. The Drucker Prager-yield function was chosen to reflect the pressure dependence of the ice and the routine describing the Drucker-Prager yield function has been proved that it can work properly in the simulation. Based on the investigated ice material model, the pressure dependent feature is added into this user defined material model.Item Open Access Idealisation error control for aerospace virtual structural testing(Cranfield University, 2009-03) Hetey, Laszlo; Campbell, JamesThis thesis addresses idealisation error control for the nonlinear finite element method. The focus is on accurate failure prediction of mid-size aerospace structures. The objective is the development of technologies that shorten the certification process of new airplanes, by replacing expensive and time consuming testing with reliable calculation methods. The SAFESA (Safe Structural Analysis) approach was applied to the collapse analyses of stiffened metal panels. ABAQUS/Standard was thereby the utilised nonlinear solver. Because the original SAFESA procedure is tailored for linear analyses, the methodology needed an update. The first analysis case is a stiffened panel compression test which was arranged as a lecture demonstration at Cranfield University. The analysis behaviour is highly nonlinear due to the thin-walled properties of the panel. The second analysis investigates an Airbus compression panel. Until failure, the panel behaves geometrically less complicated because the major load bearing parts are thick-walled and bend smoothly. The main research work is the critical analysis of important modelling assumptions concerning the used material model, boundary conditions and geometrical imperfections. In both cases, the method helped to identify idealisation errors and to build a reliable FEM model. In order to deal with the nonlinear error sources, minor extensions to the original method had to be made. The major achievement is the development of the first expert system which applies the idealisation error control methodology. CAD data import, geometry visualization, a knowledge-based decision making advisor and audit trail functionality were implemented. The expert system leads the user through a step-by-step idealisation process. Each decision is documented and a confidence level must be supplied. This way, every uncertainty is flagged out as potential error source. An interactive interface was created, which provides the user with expert advice on how to treat the idealisation errors. The software has been validated and shown to meet the program objectives.Item Open Access Modelling evolution of anisotropy in metals using crystal plasticity(Cranfield University, 2013-03) Chaloupka, Ondrej; Campbell, JamesMany metals used in modern engineering exhibit anisotropy. A common assumption when modelling anisotropic metals is that the level of anisotropy is fixed throughout the calculation. As it is well understood that processes such as cold rolling, forging or shock loading change the level of anisotropy, it is clear that this assumption is not accurate when dealing with large deformations. The aim of this project was to develop a tool capable to predict large deformations of a single crystal or crystalline aggregate of a metal of interest and able to trace an evolution of anisotropy within the material. The outcome of this project is a verified computational tool capable of predicting large deformations in metals. This computational tool is built on the Crystal Plasticity Finite Element Method (CPFEM). The CPFEM in this project is an implementation of an existing constitutive model, based on the crystal plasticity theory (the single crystal strength model), into the framework of the FEA software DYNA3D® . Accuracy of the new tool was validated for a large deformation of a single crystal of an annealed OFHC copper at room temperature. The implementation was also tested for a large deformation of a polycrystalline aggregate comprised of 512 crystals of an annealed anisotropic OFHC copper in a uniaxial compression and tension test. Here sufficient agreement with the experimental data was not achieved and further investigation was proposed in order to find out the cause of the discrepancy. Moreover, the behaviour of anisotropic metals during a large deformation was modelled and it was demonstrated that this tool is able to trace the evolution of anisotropy. The main benefit of having this computational tool lies in virtual material testing. This testing has the advantage over experiments in time and cost expenses. This tool and its future improvements, which were proposed, will allow studying evolution of anisotropy in FCC and BCC materials during dynamic finite deformations, which can lead to current material models improvement.Item Open Access Modelling of nonlinear behaviour of metallic structure components(Cranfield University, 2004-09) Mirkovic, J.; Campbell, JamesEngineering has seen an increase in the use of computer simulations over experiments, in order to save time and reduce costs. The improvement of simulation tools continues with the objective of decreasing the difference between the results of numerical simulations and structural response in real mechanical processes. This study was focused on the improvement of simulation tools that will be used in aerospace crashworthiness, with the common type of problem defined as high-Velocity impact loading of thin-walled aluminium alloy structures. In order to achieve the defined task it was decided to develop a suitable material model that can provide the correct material response in the numerical simulations. The material model is developed as a part of the DYNA3D code and can be used for both solid and shell elements. Three phenomena that are essential for impact loading and that are incorporated in the material model are anisotropy, strain rate and temperature dependency, and material failure. The level of anisotropy that is treated is orthotropy which is a good approximation for sheet metal. For the purpose of providing more accurate results of dynamically loaded structures, a strain rate and temperature dependent flow stress definition was added to the material model. Based on the elastic-plastic algorithm with orthotropy and strain rate dependency, a tensile damage model was established. The current 3D damage/failure model is porosity based and allows for the modelling of tensile failure. The model can be applied to impact loading and both shell and solid elements. The performance of the developed material model was investigated by using a series of test cases, including helicopter impact on rigid surface, and the comparison of simulation results to experimental data. It was shown that the developed model provides improved material description in the simulation of aluminium alloys behaviour.Item Open Access Non-linear idealisation error analysis of an aerospace stiffened panel loaded in compression(Sage, 2013-08-12) Hetey, Laszlo; Campbell, James; Vignjevic, RadeThe SAFE Structural Analysis procedure is an idealisation error control methodology devised for linear static finite element analysis. This study examines the applicability of this process to non-linear problems. The studied case is the collapse analysis of an aircraft stiffened panel loaded in compression. This article presents the critical investigation of important modelling assumptions, including the joint modelling, boundary conditions, geometrical imperfections and scattering in material parameters. Potential error sources are identified and then analysed using the non-linear finite element solver ABAQUS. The analysis derived an improved finite element model and concrete idealisation error estimates. The finally simulated failure behaviour corresponds well to the data measured in the test.Item Open Access Prediction of material damage in orthotropic metals for virtual structural testing(Cranfield University, 2010-12) Ravindran, S.; Campbell, JamesModels based on the Continuum Damage Mechanics principle are increasingly used for predicting the initiation and growth of damage in materials. The growing reliance on 3-D finite element (FE) virtual structural testing demands implementation and validation of robust material models that can predict the material behaviour accurately. The use of these models within numerical analyses requires suitable material data. EU aerospace companies along with Cranfield University and other similar research institutions have created the MUSCA (non-linear MUltiSCale Analysis of large aero structures) project to develop virtual structural testing prediction. The MUSCA project focuses on static failure testing of large aircraft components. It aims to reduce laboratory tests using advanced numerical analysis to predict failure in order to save overall cost and development time. This thesis aims to improve the current capability of finite element codes in predicting orthotropic material behaviour, primarily damage. The Chow and Wang damage model has been implemented within ABAQUS as a VUMAT subroutine. This thesis presents the development of a numerical damage prediction model and an experimental study to develop a damage material characterisation process that can easily be performed using standard tensile test specimen and equipment already available in the aerospace industry. The proposed method makes use of Digital Image Correlation (DIC), a non-contact optical strain field measurement technique. Experiments were conducted at Cranfield University material testing facility on aerospace aluminium alloy material AA-2024-T3 and AA-7010-T7651. After thorough literature survey a complete new method was formulated to implement Chow and Wang damage model in Abaqus Explicit numerical code. The damage model was successfully implemented for isotropic and orthotropic behaviour using single element model, multi-element coupon test model and a simple airframe structure. The simulation results were then verified with the similar experimental results by repeating the experimental procedure using simulation for each material type and found matching results. The model is then compared with experimentally determined orthotropic material parameter for AA2024 and AA7010 for validation and found agreeable results for practical use. The material characterisation of damage parameters from standard tensile specimen using DIC technique was also demonstrated and the procedures were established. In this research the combination of experimental work and numerical analysis with clear and simpler calibration strategy for damage model is demonstrated. This is the important contribution of this research work and the streamlined procedures are vital for the industry to utilise the new damage prediction tools. The damage model implementation and test procedures developed through this research provide information and processes involved in fundamentally predicting the ductile damage in metals and metal alloys. The numerical damage model developed using the well-defined verification and validation procedures explained in this research work with new streamlined damage material characterisation using recent contact less DIC technique has wider implication in the material model development for ductile metals in general. The thesis ultimately delivered a fully verified, validated robust damage model numerical simulation code with a new DIC damage characterisation procedure for practical application. The model is now used by the aerospace industry for predicting damage of large aircraft structures.Item Open Access Smoothed particle hydrodynamics modelling for failure in metals(Cranfield University, 2010-03) Strand, Russell K; Campbell, JamesIt is generally regarded to be a difficult task to model multiple fractures leading to fragmentation in metals subjected to high strain rates using numerical methods. Meshless methods such as Smoothed Particle Hydrodynamics (SPH) are well suited to the application of fracture mechanics, since they are not prone to the problems associated with mesh tangling. This research demonstrates and validates a numerical inter-particle fracture model for the initiation, growth and subsequent failure in metals at high strain rate, applicable within a Total Lagrangian SPH scheme. Total Lagrangian SPH performs calculations in the reference state of a material and therefore the neighbourhoods remain fixed throughout the computation; this allows the inter-particle bonds to be stored and tracked as material history parameters. Swegle (2000) showed that the SPH momentum equation can be rearranged in terms of a particle-particle interaction area. By reducing this area to zero via an inter-particle damage parameter, the principles of continuum damage mechanics can be observed without the need for an effective stress term, held at the individual particles. This research makes use of the Cochran-Banner damage growth model which has been updated for 3D damage and makes the appropriate modifications for inter-particle damage growth. The fracture model was tested on simulations of a 1D flyer plate impact test and the results were compared to experimental data. The test showed that the model can recreate the phenomena associated with uniaxial spall to a high degree of accuracy. Some limited modelling was also conducted in 2 and 3 dimensions and promising results were observed. Research was also performed into the mesh sensitivity of the explosively driven Mock- Holt experiment. 3D simulations using the Eulerian SPH formulation were conducted and the best results were observed with a radial packing arrangement. An in-depth assessment of the Monaghan repulsive force correction was also conducted in attempt to eliminate the presence of the SPH tensile instability and stabilise the available Eulerian SPH code. Successful results were observed in 1D, although the results could not be replicated consistently in 2D. A further study was also conducted into an approach that makes use of a partition of unity weighting to two different SPH approximations of the same flow-field; one local and one non-local (or extended). Unfortunately this approach could not be made to stabilise the code.Item Open Access Toward a rigorous derivation of a stable and consistent smoothed particle hydrodynamics method(Cranfield University, 2015-11) Munro, David; Campbell, JamesThe aim of this thesis is to provide an investigation toward a rigorous derivation of a stable and consistent numerical method based on the established Smoothed Particle Hydrodynamics method. The method should be suitable for modelling the large deformation transient response of fluids and solids, the interests of the Crashworthiness, Impact and Structural Mechanics group (CISM) at Cranfield University. A literature review of the current state of the art of the SPH method finds that the conventional SPH equations are not derived in a rigorous way, often the equations are manipulated into a mathematically equivalent form in order to preserve conservation of linear momentum, which often leads to different results; the reasons for this are unknown and it is not fully understood how each particular form of the discrete equations effects the solution in terms of stability, accuracy and convergence. This leads to specific objectives being defined which underpin the overall aim of the thesis. The first objective is to develop an understanding of the SPH method and the implementation used at Cranfield University, this is done through a capability study which demonstrates the coupled SPH-FE method and a number of relevant improvements to the MCM code including the addition of a turbulence model and the modification of the SPH contact algorithm to model lateral forces between materials. This is demonstrated through the implementation of a friction model, which suggests that the contact algorithm is suitable for resolving lateral forces based on the relative velocity between materials, with the potential for coupling with a structural FE model ... [cont.].Item Open Access Virtual testing of post-buckling behaviour of metallic stiffened panel(Cranfield University, 2011-12) Wang, Yang; Campbell, JamesThe aim of the project presented in this thesis is to demonstrate a modelling method for predicting the variability in the ultimate load of stiffened panel under axial compression due to manufacturing variability. Bulking is sensitive to imperfections. In the case of a post-buckled panel, manu-facturing variability produces a scatter in the ultimate load. Thus, reasonable leeway for imperfections and inherent variability must be allowed in their design. Firstly, a finite element model of a particular stiffened panel was developed, and all nonlinearities within the material, boundary condition and geometry were considered. Verification and validation were performed to examine the accuracy of the buckling behaviour prediction, especially ultimate load. Experiments on 5 identical panels in design were performed to determine the level of panel-panel variation in geometry and collapse load. A data reduction programme based on the practical geometry scanning was developed, in addi-tion to which, the procedure of importing measured imperfection into Finite Ele-ment model was introduced. To identify and apply representative imperfections to the panel model, a double Fourier series representation of the random geometric distributions is attempt-ed, and was used thereby to derive a series of shapes representing random ge-ometry scatters. With these newly generated geometric imperfections, the variation in collapse load was determined, using the validated FE analysis. And also, the probability of these predicted loads was generalized.