Browsing by Author "Pickett, A. K."
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Item Open Access Damage and failure modelling of carbon and glass 2D braided composites(Cranfield University, 2006-04) Fouinneteau, M. R. C.; Pickett, A. K.Composite materials have been increasingly used in the past two decades since they offer significant potential weight reduction, part design flexibility and improved specific mechanical performance compared to traditional metals. For specific applications, braid reinforced composites offer better near net shape part and manufacturing flexibility than conventional unidirectional laminates, albeit at the expense of slightly lower in-plane stiffness and strength. Furthermore, for impact and crash applications, which is the emphasis of this thesis, their tow waviness and interlocking can offer excellent damage tolerance and energy absorption. In this work, heavy tow (24k) biaxial carbon and glass braided preforms were used to manufacture coupons and beam structures to undertake an extensive testing campaign to characterise different damage and failure mechanisms occurring in braided composites. Due to large shear deformation and surface degradation, non conventional measurement techniques based on marker tracking and Digital Image Correlation were successfully used to measure strains in the damaging material. The modelling of braided composites was conducted using the meso-scale damage approach first proposed by P. Ladevèze for unidirectional composites. The calibration of an equivalent braid unidirectional ply was achieved using the experimental results obtained for different braided coupons. Furthermore, failure mechanisms observed experimentally, such as tow stretching and fibre re-orientation occurring during loading history, were integrated into the model. A new unidirectional ply formulation was subsequently implemented into the explicit finite element code PAM-CRASHTM. Validation of the new model using single element, coupons and beams were conducted that provided a satisfying correlation between experimental tests and numerical predictions.Item Open Access Damage and failure modelling of carbon/epoxy non-crimp fabtic composites(Cranfield University, 2005-06) Greve, Lars; Pickett, A. K.Abstract not availableItem Open Access Experimental and finite element draping simulation for non-crimp and twill fabrics(2002-09) Creech, G; Pickett, A. K.For low cost and high volume composite manufacture, Liquid Composite Moulding (LCM) techniques such as Resin Transfer Moulding (RTM) are of increasing industrial interest. These techniques involve draping of fabric reinforcement layers into a mould for subsequent resin transfer. For composite materials to compete with metals in low cost, high volume manufacture, valid simulation of this fabric draping is necessary to ascertain if a fabric can be draped without forming defects. Additional permeability and mechanical analysis is reliant upon accuracy in this initial simulation stage. Therefore, this study experimentally and numerically investigates the deformation mechanisms of a woven 2/2 twill fabric and Non-Crimp Fabric (NCF) with the aim of validating a draping simulation code. PAMFORM™ is used as the basis for this work. A material model included in the code is investigated for the 2/2 twill, while a new NCF material representation is proposed to account for additional through thickness stitching constraints. Draping trials over a double hemisphere mould are conducted for final validation of material data calibrated through an extensive testing programme. Both bias extension and picture frame tests are conducted to characterise the shear behaviour of each materialItem Open Access Experimental investigation and numerical modelling of composite-honeycomb materials used in Formula 1 crash structures(Cranfield University, 2007-01) Lamb, A. J.; Pickett, A. K.This thesis has investigated composite-honeycomb sandwich materials commonly used in Formula 1 nosecone structures. Experimental work has investigated their failure behaviour under static and dynamic crash loading, from which new constitutive failure laws for implementation in the explicit Finite Element code PAM-CRASHTM have been proposed. An investigation using an improved Arcan apparatus has been conducted to establish the mixed shear-compression properties of the honeycomb. An investigation has also been performed to establish relationships between in-plane deformation and out-ofplane compression properties. These relationships have been identified and successfully implemented into a honeycomb solid element material model available in PAMCRASHTM. A further investigation to represent honeycomb using geometrically accurate shell representation of the honeycomb has also been presented. This model was shown to reproduce trends observed during testing. The composite skin material has also been experimentally investigated and presented. This investigation made use of digital image correlation to examine the onset of intralaminar shear failure mechanisms, from which a non-linear damage progression law was identified. This law was successfully implemented into the Ladevéze damage model in PAM-CRASHTM for composite material modelling and has been shown to improve the representation of in-plane shear damage progression and failure. A series of experimental investigations to examine the energy absorbing properties of the sandwich have been conducted and presented. These investigations include three point bend flexural testing and edgewise impact loading. Failure mechanisms in the skin and core have been identified for each loading case. Experimental findings were used to assess the capability of PAM-CRASHTM for sandwich material modelling. This investigation has highlighted deficiencies in the material models when representing the sandwich, specifically with the existing composite skin and honeycomb models. Improvements introduced to the core and skin material models have shown some improvement when representing sandwich structures.Item Open Access Manufacture of a rotor blade pitch horn using binder yarn fabrics(International Committee on Composite Materials, 2009-07-31) Weiland, F.; Weimer, C.; Katsiropoulos, C. V.; Pantelakis, S. G.; Asareh, Mehdi; Cartié, Denis; Mills, Andrew; Skordos, Alexandros A.; Dufort, L.; De Luca, P.; Pickett, A. K.The use of binder yarn fabrics in rotor blade applications is investigated in this work. A preforming procedure is incorporated in manufacturing, resulting in higher degree of automation and a reduction of process steps. The performance of the process is evaluated with respect to cost savings compared to prepregging technologies.Item Open Access Mesoscopic Finite Element modelling of non-crimp fabrics for drape and failure analyses(Cranfield University, 2006-04) Creech, G.; Pickett, A. K.To date, macroscopic analysis methods have been invariably used to analyse textile composite structures for forming and mechanical performance. Techniques such as geometric ‘mapping’ for the draping of textile fabrics and classical laminate analysis combined with simplified failure criteria to determine mechanical performance have formed the basis of most of these methods. The limited accuracy of the physical laws applied is appropriate to macro- analysis methods in which the fibre-matrix composite is treated as homogeneous medium. Today, however, modern high performance computers are opening new possibilities for composites analysis in which far greater detail of the composite constituent materials may be made. This paper presents Finite Elements techniques for the draping simulation of textile composites, specifically biaxial Non Crimp Fabrics, in which the complex deformation mechanisms of the dry tows and stitching may be properly modelled at the individual tow and stitch mesoscopic level. The resulting ‘deformed’ Finite Element model is then used to provide a basis for accurate simulation of the impregnated composite structure. The modelling techniques for both draping and structural analysis are presented, together with validation results for the study of a relatively large scale hemisphere composite part.