1,721,247 research outputs found
Design and characterisation of advanced pseudo-ductile unidirectional thin-ply carbon/epoxy-glass/epoxy hybrid composites
Get PDFA comprehensive set of thin-ply pseudo-ductile unidirectional interlayer hybrid composite materials comprising S-glass and a variety of thin carbon prepregs was designed and characterised. Unique elastic-yielding-hardening type stress-strain responses similar to those of ductile metals were achieved through fragmentation and stable pull-out of the carbon layers, generating a range of initial moduli, pseudo-yield strains, plateau stresses and pseudo ductile strains for the various configurations. The typical failure modes of thin-ply hybrid composites were highlighted in four series of stress-strain graphs obtained for the same materials with different carbon layer thicknesses. The predicted failure modes agreed well with the experimental results and demonstrated the merit of our two step design framework based on (i) simple analytical criteria and (ii) novel damage mode maps
Multi-directional hybrid laminates-studying the effect of fragmentation and dispersed delamination on stress-strain curves of unnotched laminates using analytical modelling.
No full textHybridisation is one of the approaches to introduce pseudo-ductility to brittle composite materials. In this approach, two or more different types of fibre are combined and if the configuration and material constituents are well selected, the tensile response shows a gradual failure and pseudo-ductile strain. Different types of hybrid composites with continuous layers have been studied to produce pseudoductile tensile behaviour. However, most hybrid material studies to date have been focused on Uni- Directional (UD) laminates which are not usually applied in industry due to poor transverse mechanical properties.In this study, the behaviour of multi-directional hybrid laminates made with UD hybrid sub-laminates is studied. The final goal is to introduce pseudo-ductility to layups with wider industrial applications. The effect of layup as well as the UD building-block stress-strain curve on the final stress-strain curve of the laminate is also studied.A new analytical approach based on Classical Laminate Theory is introduced in which the effect of different damage modes in UD hybrid laminates (fragmentation and dispersed delamination) is taken into account. The output of this method is the non-linear stress-strain curve of a multi-directional laminate with UD hybrid sub-laminates. This method is then used to study the effect of different parameters such as the mechanical properties of the constituents (low and high strain materials) and layup on the pseudo-ductility
Compressive failure strain of unidirectional carbon fibre composites from bending tests
No full textOne of the major difficulties in establishing material properties for composites is to obtain reliable compressive strengths either from the current direct compressive testing methods due to the stress concentration or from the indirect flexural tests due to the localised stress concentration and strain gradient effect. In the present paper, unconventional flexural tests on carbon fibre/wood sandwich and monolithic composite beams have been developed and compressive failure strains of unidirectional carbon fibre composites have been obtained with high values and low variability. The compressive strain of 1.36 % obtained for the IM7/8552 material is 14 % higher than the highest published value found and the variability is only 3 %. Strain gradient effects on the compressive failure strain from measurements with the same stressed volume have also been quantified for the first time using the proposed carbon fibre/wood sandwich beam with various wood core depths. The increase in failure strain due to the strain gradient effect reduced with the increase of total beam thickness and approached a constant value when the beam was thicker than 20 mm
Development of pseudo-ductile hybrid composites with discontinuous carbon- and continuous glass prepregs: 16th European Conference on Composite Materials, ECCM 2014
No full textSandwich (layer-by-layer) type hybridisation is a promising method to overcome the brittle and usually catastrophic failure of conventional composites. The new concept of combining discontinuous and continuous layers to improve the performance of hybrid composites is presented. The paper reports on the pseudo-ductility demonstrated with unidirectional discontinuous carbon/continuous glass sandwich hybrid composites. The stress-strain response of the new material architecture was analysed, and the pseudo yield strains of various specimen configurations were accurately predicted using an approach based on mode II energy release rate calculations. The effect of specimen thickness and carbon platelet length on the stress-strain response was studied and presented
Demonstration of pseudo-ductility in unidirectional hybrid composites made of discontinuous carbon/epoxy and continuous glass/epoxy plies
Get PDFA new, partially discontinuous architecture is proposed to improve the mechanical performance of pseudo-ductile, unidirectional (UD) interlayer carbon/glass hybrid composites. The concept was successfully demonstrated in different laminates with high strength and high modulus carbon and S-glass epoxy UD prepregs. The novel hybrid architecture provided pseudo-ductile tensile stress-strain responses with a linear initial part followed by a wide plateau and a second linear part, all connected by smooth transitions. The best hybrid configuration showed 60% improvement in modulus compared to pure glass, 860 MPa plateau stress and 2% pseudo-ductile strain. The initial modulus, the plateau stress and the overall tensile stress-strain response of each specimen configuration were predicted accurately.</p
Full-field assessment of the damage process of laminated composite open-hole tensile specimens. Part I: methodology
No full textThe present paper is the first part of a study dedicated to the assessment of the damage taking place in composite open-hole tensile specimens using full-field strain measurements. It concentrates on the thorough validation of the methodology used to process the full-field data. First, the grid method used to provide the two components of the in-plane displacement field at the surface of the test specimens is described. Then, the data processing procedure to obtain the displacement maps during the test is discussed. The main part of the paper is dedicated to the derivation of strains from displacements, investigating two procedures: local differentiation and polynomial fitting. The effect of the grid is also investigated. Finally, successful experimental results are presented. (c) 2007 Elsevier Ltd. All rights reserved.</p
Hybrid specimens eliminating stress concentrations in tensile and compressive testing of unidirectional composites
Get PDFTwo novel approaches are proposed for elimination of stress concentrations in tensile and compressive testing of unidirectional carbon/epoxy composites. An interlayer hybrid specimen type is proposed for tensile testing. The presented finite element study indicated that the outer continuous glass/epoxy plies suppress the stress concentrations at the grips and protect the central carbon/epoxy plies from premature failure, eliminating the need for end-tabs. The test results confirmed the benefits of the hybrid specimens by generating consistent gauge-section failures in tension. The developed hybrid four point bending specimen type and strain evaluation method were verified and applied successfully to determine the compressive failure strain of three different grade carbon/epoxy composite prepregs. Stable failure and fragmentation of the high and ultra-high modulus unidirectional carbon/epoxy plies were reported. The high strength carbon/epoxy plies exhibited catastrophic failure at a significantly higher compressive strain than normally observed
Parametric study of failure mechanisms and optimal configurations of pseudo-ductile thin-ply UD hybrid composites
Get PDFThe effect of different parameters on the gradual failure and pseudo-ductility of thin UD hybrids is studied using an analytical method developed recently. Damage mode maps are proposed to show the effect of different geometric parameters for a specific material combination. This type of map is a novel and efficient method to find the optimum configuration of UD hybrids and also indicates the importance of thin layers to achieve the optimum geometric parameters in practice. The material parametric study reveals that there is always a trade-off between the "yield stress" and the amount of pseudo-ductility; higher yield stresses leads to lower pseudo-ductility and vice versa. However, application of high-stiffness fibres with high strengths as the low strain material can provide both better pseudo-ductility and yield stress.</p
Demonstration of pseudo-ductility in all fibre directions of high performance quasi-isotropic thin ply carbon/glass hybrid composites: 21st International Conference on Composite Materials, ICCM 2017
No full textHybridisation is one of the approaches to introduce pseudo-ductility to brittle composite materials. In this approach, two or more different types of fibre are combined and if the configuration and material constituents are well selected, the tensile response shows a gradual failure and a metal-like stress-strain curve with a pseudo-yield point. Different types of unidirectional and quasi-isotropic (QI) hybrid composites with continuous layers have been studied to produce pseudo-ductile tensile behaviour in one loading orientation when subjected to tension. However, most composite structures are subjected to multiple loading orientations, therefore, the aim of this paper is to exploit the potential of thin-ply carbon/glass hybrid laminates with dispersed orientations to generate high performance QI composite plates that show pseudo-ductility in all the fibre orientations under tensile loading. QI sublaminates were used to fabricate novel architectures made up of a QI Skyflex thin ply high strength T300-carbon/120°C epoxy sub-laminates sandwiched between the two QI Hexcel standard thickness S-glass/913 epoxy sub-laminates. The results show that by choosing an appropriate ratio of the carbon thickness to the laminate thickness and material properties, a desirable pseudo-ductile failure can be achieved in all the fibre orientations
Damage mode maps and parametric study of thin UD hybrid composites: 16th European Conference on Composite Materials, ECCM 2014
No full textHybridisation is one of the approaches to introduce pseudo-ductility to brittle composite materials. In this approach, two layers with different types of fibre are combined and a new stress-strain response which depends on the material properties of the components and thickness of the constituents is produced. In this paper, an analytical method of predicting the damage progress of UD hybrids is proposed which has an acceptable accuracy and is significantly faster than numerical methods such as FE. A new chart called a "damage mode map" is produced that relates the configuration of a UD hybrid to its predicted damage scenario straightaway. This map has been found to be a very useful tool to find the optimum configuration in designing new hybrid composites
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