Browsing by Author "Pickett, Anthony K."

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    Effect of tufting on the response of non crimp fabric composites.
    (2007-09-01T00:00:00Z) Colin de Verdiere, Mathieu; Pickett, Anthony K.; Skordos, Alexandros A.; Witzel, Volker
    This paper examines the effectiveness of tufting in enhancing the through the thickness properties of non crimped fabrics. The response of tufted and untufted carbon/epoxyn on crimped fabric composites produced using resin infusion is investigated in axial tension and compression and cyclic [±45] loading. The out- of-plane response is studied in mode I and mode II delamination tests. Tufted material has significantly higher delamination resistance and lower in plane properties in tension and compression. Tufted and untufted non crimp fabric composites have similar response in shearin terms of both plastic strain and strength. Optical strain measurements allowed monitoring of the two dimensional damage field incyclic experiments. Damage tends to be localised in untufted specimens, where as it becomes more uniform across the width of specimens with tufts. Material models for untufted and tufted non crimped fabric composites simulating both non-linear in-plane behaviour and delamination damage were developed. Material parameters were estimated from experimental results, and both material submodels were implemented in a commercial explicit finite element code which allows the in corporation of delamination behaviour using cohesive interface elements. A comparison of experiments and finite element model results simulating coupons verified the implementation of the models
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    Failure prediction for advanced crashworthiness of transportation vehicles.
    (Elsevier, 2004-08) Pickett, Anthony K.; Pyttel, Thomas; Payen, Fabrice; Lauro, Franck; Petrinic, Nikica; Werner, Heinz; Christlein, Jens
    During the past two decades explicit finite element crashworthiness codes have become an indispensable tool for the design of crash and passenger safety systems. These codes have proven remarkably reliable for the prediction of ductile metal structures that deform plastically; however, they are not reliable for joining systems and materials such as high strength steels, plastics and low ductility lightweight materials all of which are liable to fracture during the crash event. In order to improve crash failure prediction of materials and joining systems the CEC has recently funded a 3 year European research project dedicated to this topic. Specifically the project concerned aluminium, magnesium, high strength steels, plastics and two primary joining techniques; namely spotwelds and weldlines. Numerous new developments were undertaken including improved failure laws, adaptive meshing and element splitting to treat crack propagation. In the case of sheet stamping, investigations have also tried to account for process history effects and the metallurgical changes that occur during manufacture. This project has recently finished and this paper presents some of the key research results of the work concerning materials failure modelling.
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    Material characterisation and calibration of a meso-mechanical damage model for braid reinforced composites
    (Elsevier Science B.V., Amsterdam., 2006-02-01T00:00:00Z) Pickett, Anthony K.; Fouinneteau, M. R. C.
    Cost effective braid reinforced composites are a potential substitute for metals in many automotive structural applications where good mechanical performance combined with high energy absorption are of special interest. This paper presents experimental work undertaken to characterise braided composites and a meso-mechanical damage model suitable for the impact and crash analysis of braided composites. The model presented correctly represents stiffness, initial failure and the post failure damage response, which is of particular importance for crash applications. Furthermore, work is presented that describes testing procedures, which should be followed in order to obtain the correct material parameters for analysis. Finally, validation of the testing procedures and the constitutive model is made against a structural braid reinforced composite beam loaded to failure under four point bending.
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    Modelling damage and failure in carbon/epoxy non-crimp fabric composites including effects of fabric pre-shear
    (Elsevier, 2006-11) Greve, L.; Pickett, Anthony K.
    A numerical material model for intra-laminar failure prediction of biaxial non-crimp fabric composites is presented. The model combines the elasto-plastic continuum damage constitutive model proposed by Ladevèze with the intra-laminar matrix failure model of Puck, and improves the shear damage representation using an exponential damage function. The work focuses on numerical model development for damage and failure prediction and validation for both unsheared and sheared fabric composites which will result from draping of the fabric preform over a double curved geometry in order to manufacture complex shaped parts. An extensive test program has been conducted using flat composite coupons with differing degrees of fabric pre-shear in order to establish a database of material stiffness, strength, and in-plane matrix shear damage evolution prior to failure. This database is used to identify parameters for the proposed ‘Ladevèze-Puck’ damage and failure model. Final validation has been made by implementing the model in an explicit Finite Element code and performing a series of experimental and simulation analyses on transversely loaded circular composite discs having differing degrees of fabric pre-shear. The model has been shown to successfully capture intra-ply failure modes in the principle fibre directions for tension and compression, intra-ply shear and also the interaction of these modes.
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    A Simplified Discrete Finite Element Model for Non-crimp Fabric Composites
    (2008-06-01T00:00:00Z) Knipprath, Christian; Skordos, Alexandros A.; Pickett, Anthony K.
    In this paper a simplified discrete finite element model for composite materials is introduced. This model allows the discrete representation of both the fibre tows and the resin on a meso-scale level. The capability to assign different material properties to each fibre tow and resin zones allows the investigation of local reinforcements in composites. This modelling concept is combined with a three dimensional damage model and is successfully implemented in a finite element code. Results indicate that relatively fast model analysis and successful approximation of fibre and resin failure under specific load cases may be investigated.