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Andreas Mortensen - One of the best experts on this subject based on the ideXlab platform.
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tensile elongation of unidirectional or laminated composites combining a brittle reinforcement with a ductile Strain and Strain rate hardening Matrix
Acta Materialia, 2014Co-Authors: Amael Cohades, Andreas MortensenAbstract:We use the long-wavelength model of Hutchinson and Neale (1977) and Ghosh (1977) to estimate the uniform tensile elongation of two-phase composites deforming quasistatically according to the equiStrain rule of mixtures, in which one phase is ductile while the other fractures progressively according to two-parameter Weibull statistics. We use shear-lag models in the literature to quantify load transfer from the ductile phase to the fractured brittle phase, and to estimate the influence of Matrix Strain and Strain-rate hardening, of brittle phase fracture characteristics, and of phase volume and strength ratios, on the composite Strain to failure as dictated by the onset of unstable necking. Calculations show that Strain and Strain-rate hardening of the ductile phase do relatively little to increase the ductility of the composite. Two parameters play a dominant role, namely the brittle-phase Weibull modulus and a dimensionless parameter describing load transfer across the two phases. The main practical implication of this analysis is that, to produce reasonably ductile two-phase composites, the best strategy is to aim for small layer thicknesses. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Tensile elongation of unidirectional or laminated composites combining a brittle reinforcement with a ductile Strain and Strain-rate hardening Matrix
Acta Materialia, 2014Co-Authors: Amael Cohades, Andreas MortensenAbstract:We use the long-wavelength model of Hutchinson and Neale (1977) and Ghosh (1977) to estimate the uniform tensile elongation of two-phase composites deforming quasistatically according to the equiStrain rule of mixtures, in which one phase is ductile while the other fractures progressively according to two-parameter Weibull statistics. We use shear-lag models in the literature to quantify load transfer from the ductile phase to the fractured brittle phase, and to estimate the influence of Matrix Strain and Strain-rate hardening, of brittle phase fracture characteristics, and of phase volume and strength ratios, on the composite Strain to failure as dictated by the onset of unstable necking. Calculations show that Strain and Strain-rate hardening of the ductile phase do relatively little to increase the ductility of the composite. Two parameters play a dominant role, namely the brittle-phase Weibull modulus and a dimensionless parameter describing load transfer across the two phases. The main practical implication of this analysis is that, to produce reasonably ductile two-phase composites, the best strategy is to aim for small layer thicknesses. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Ductility of Saffil short fibre reinforced metals
Scripta Materialia, 2005Co-Authors: Ludger Weber, Reza Tavangar, Andreas MortensenAbstract:It is proposed that a critical combination of Matrix Strain hardening exponent and fibre volume fraction must be exceeded to confer attractive tensile ductility to short-fibre reinforced metal. C 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
R. J. Young - One of the best experts on this subject based on the ideXlab platform.
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Experimental studies on the interfacial shear-transfer mechanism in discontinuous glass-fibre composites
Composites Science and Technology, 2000Co-Authors: John L. Stanford, Peter A. Lovell, C. Thongpin, R. J. YoungAbstract:Interfacial stress/Strain distributions in discontinuous glass-fibre/epoxy composites have been determined experimentally for the first time by the simultaneous use of tensile deformation measurements and Raman spectroscopy. Model single-fibre composites were used and the glass fibres were coated with a diacetylene-urethane copolymer which was thermally cross-polymerised. During composite deformation, the stress-induced band shifts of C≡C in the polydiacetylene phases of the coating were used to map the Strain distribution along a fibre as a function of overall Matrix Strain up to fibre fracture. Measured Strain distributions in fibres were analysed by using classical shear-lag theory to determine interfacial shear-stress distributions. Fibre fragmentation was monitored in detail up to saturation, and the limiting value of interfacial shear stress is shown to be determined by the shear yield stress of the Matrix.
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Fragmentation in alumina fibre reinforced epoxy model composites monitored using fluorescence spectroscopy
Journal of Materials Science, 1996Co-Authors: R. B. Yallee, M. C. Andrews, R. J. YoungAbstract:It has been found that well-defined fluorescence R_1 and R_2 lines can be obtained from PRD-166 alumina-zirconia fibres and that the fluorescence R lines shift with applied stress. They are found to shift to higher wavenumber when subjected to tensile deformation and to lower wavenumber in compression. The stress-sensitive fluorescence R_2 line has been used to map the distribution of stress along PRD-166 fibres embedded in an epoxy resin Matrix cured under different conditions. It has been shown that the distributions of stress along the PRD-166 fibres at different levels of Matrix Strain are consistent with those predicted by conventional shear-lag analysis. The interfacial shear stress has been derived from the point-to-point variation of stress along the fibre. The fluorescence technique has also been used to map the stress distribution along a PRD-166 fragment in an epoxy Matrix during a single-fibre fragmentation test where it is found that debonded regions propagate along the fibre fragments during loading, after initial fragmentation has occurred.
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Interfacial failure in ceramic fibre/glass composites
Composites Part A: Applied Science and Manufacturing, 1996Co-Authors: R. J. Young, X. YangAbstract:Abstract The interfacial micromechanics have been investigated for single-fibre model composites consisting of single PRD-166 alumina/zirconia fibres, both carbon-coated and uncoated, in a glass Matrix using fluorescence spectroscopy to follow axial fibre deformation. It has been shown that the presence of the carbon coating leads to a weaker interface. The fibre—Matrix interface for the coated fibres is found to break down at lower levels of Matrix Strain than for the uncoated fibres when the composite is subjected to axial tensile deformation. The maximum interfacial shear stress is also found to be lower for the carbon-coated fibres.
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Analysis of the deformation of aramid fibres and composites using Raman spectroscopy
Journal of Raman Spectroscopy, 1993Co-Authors: M. C. Andrews, R. J. YoungAbstract:It is demonstrated that Raman spectroscopy can be used to study both the deformation micromechanics of high-performance aramid polymer fibres and of these fibres in model, single-fibre epoxy resin Matrix composites. It is shown that the peak position of the 1610 cm−1 aramid Raman band shifts to lower frequency under the action of tensile stress or Strain due to the macroscopic deformation leading to direct stretching of the polymer molecules. These Strain-induced band shifts can be used to map the distribution of stress or Strain along a discontinuous, aramid fibre inside an epoxy resin Matrix from which the interfacial shear stress can be calculated. It is shown that the behaviour is consistent with that predicted by the classical shear-lag analysis. The technique was also used to study the fragmentation process for an aramid fibre in an epoxy resin Matrix in which the Matrix Strain exceeds the failure Strain of the fibre. It is further demonstrated that the technique can be used to compare the interfacial properties of aramid fibres where the interfacial shear stress is found to be higher for sized fibres than for those which have been de-sized.
Amael Cohades - One of the best experts on this subject based on the ideXlab platform.
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tensile elongation of unidirectional or laminated composites combining a brittle reinforcement with a ductile Strain and Strain rate hardening Matrix
Acta Materialia, 2014Co-Authors: Amael Cohades, Andreas MortensenAbstract:We use the long-wavelength model of Hutchinson and Neale (1977) and Ghosh (1977) to estimate the uniform tensile elongation of two-phase composites deforming quasistatically according to the equiStrain rule of mixtures, in which one phase is ductile while the other fractures progressively according to two-parameter Weibull statistics. We use shear-lag models in the literature to quantify load transfer from the ductile phase to the fractured brittle phase, and to estimate the influence of Matrix Strain and Strain-rate hardening, of brittle phase fracture characteristics, and of phase volume and strength ratios, on the composite Strain to failure as dictated by the onset of unstable necking. Calculations show that Strain and Strain-rate hardening of the ductile phase do relatively little to increase the ductility of the composite. Two parameters play a dominant role, namely the brittle-phase Weibull modulus and a dimensionless parameter describing load transfer across the two phases. The main practical implication of this analysis is that, to produce reasonably ductile two-phase composites, the best strategy is to aim for small layer thicknesses. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Tensile elongation of unidirectional or laminated composites combining a brittle reinforcement with a ductile Strain and Strain-rate hardening Matrix
Acta Materialia, 2014Co-Authors: Amael Cohades, Andreas MortensenAbstract:We use the long-wavelength model of Hutchinson and Neale (1977) and Ghosh (1977) to estimate the uniform tensile elongation of two-phase composites deforming quasistatically according to the equiStrain rule of mixtures, in which one phase is ductile while the other fractures progressively according to two-parameter Weibull statistics. We use shear-lag models in the literature to quantify load transfer from the ductile phase to the fractured brittle phase, and to estimate the influence of Matrix Strain and Strain-rate hardening, of brittle phase fracture characteristics, and of phase volume and strength ratios, on the composite Strain to failure as dictated by the onset of unstable necking. Calculations show that Strain and Strain-rate hardening of the ductile phase do relatively little to increase the ductility of the composite. Two parameters play a dominant role, namely the brittle-phase Weibull modulus and a dimensionless parameter describing load transfer across the two phases. The main practical implication of this analysis is that, to produce reasonably ductile two-phase composites, the best strategy is to aim for small layer thicknesses. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Costas Galiotis - One of the best experts on this subject based on the ideXlab platform.
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A study of the stress-transfer characteristics in model composites as a function of material processing, fibre sizing and temperature of the environment
Composites Science and Technology, 1997Co-Authors: A. Paipetis, Costas GaliotisAbstract:Abstract The micromechanics of reinforcement of a model composite consisting of a high-modulus fibre embedded in epoxy resin has been investigated as a function of processing conditions, namely thermal stresses, fibre sizing, and temperature. The residual stresses on single-fibre coupons were monitored for both long- and short-fibre geometries with the technique of remote laser Raman microscopy (ReRaM). The systems studied consisted of sized and unsized fibre/epoxy systems at room temperature as well as a sized system at 60 °C. Each composite was subjected to incremental tensile loading up to full fragmentation, while the stress in the fibre was monitored at each level of applied Strain. The three systems exhibited differences in the residual stress field, with the unsized fibre being in compression. The average stress in the fibre increased linearly with applied Matrix Strain up to first fracture. After fracture, the stress in the fibre was found to build from the tips of the fibre breaks, reaching a maximum value at the middle of each fragment. Two different interfacial failure modes were identified, depending on the possible initiation of a mixed-mode Matrix crack. At room temperature, the maximum interfacial shear stress for both systems was of the order of 40 MPa with the sized system exhibiting slightly better adhesion. At 60 °C, the sized system exhibited interfacial shear stress values of the order of 20 MPa.
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Effect of fibre sizing on the stress transfer efficiency in carbon/epoxy model composites
Composites Part A-applied Science and Manufacturing, 1996Co-Authors: A. Paipetis, Costas GaliotisAbstract:The micromechanics of reinforcement of a model composite consisting of continuous high-modulus fibre embedded in epoxy resin has been investigated as a function of fibre sizing. The composite was subjected to incremental tensile loading up to full fragmentation, while the stress in the fibre was monitored at each level of applied Strain with the new technique of remote laser Raman microscopy. The two systems exhibited differences in the residual stress field with the unsized fibre being in compression. The average stress in the fibre increased linearly with applied Matrix Strain up to first fracture. After fracture, the stress in the fibre was found to build from the tips of the fibre breaks, reaching a maximum value at the middle of each fragment. The shape of the stress transfer profiles indicated minor differences between the two systems at moderate Strains. At high Strains, the stress transfer profiles of the two systems were distinctly different possibly owing to the presence of two different interfacial failure modes in the two types of model composites. The maximum interfacial shear stress for both systems was of the order of 40 MPa with the sized system exhibiting slightly better adhesion. SEM examination of the fracture surfaces revealed clear interfacial failure for the unsized system whereas the sized system indicated areas of good adhesion.
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interfacial shear stress distribution in model composites part 2 fragmentation studies on carbon fibre epoxy systems
Journal of Composite Materials, 1992Co-Authors: N Melanitis, Costas Galiotis, P L Tetlow, C K L DaviesAbstract:Attention is given to the micromechanics of reinforcement of a model composite system consisting of a continuous high-modulus carbon fiber embedded in an epoxy resin. The composite was subjected to incremental tensile loading up to full fiber fragmentation, while the Strain in the fiber was monitored at each level of load using a laser Raman spectroscopic technique. The average Strain in the fiber increased linearly with applied Matrix Strain up to a value of 0.8 percent, when the first fiber fracture occurred. After fracture, the Strain in the fiber was found to build from the tips of the fiber breaks, reaching a maximum value in the middle of each fragment. The shape of the load transfer profiles at the locality of the fiber tips indicated that the stress transfer efficiency had been affected by the fracture process. The length of interfacial debonding at the point of fiber fracture was found to be driven by the Strain energy of the fractured fragments. The interfacial shear stress distributions at various levels of the applied load along individual fragments are derived from the load transfer profiles. 51 refs.
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Interfacial Shear Stress Distribution in Model Composites, Part 1: A Kevlar 49® Fibre in an Epoxy Matrix
Journal of Composite Materials, 1991Co-Authors: H. Jahankhani, Costas GaliotisAbstract:The technique of Laser Raman Spectroscopy has been applied in the study of aramid fibres, such as Kevlar 49, and aramid/epoxy interfaces. A linear relationship has been found between Raman frequencies and Strain upon loading a single Kevlar 49 filament in air. Model composites of single Kevlar 49 fibres embedded in epoxy resins have been fabricated and subjected to various degrees of mechanical deformation. The transfer lengths for reinforcement have been measured at various levels of applied tensile load and the dependence of transfer length upon applied Matrix Strain has been established. Finally, by balancing the tensile and the shear forces acting along the interface, the interfacial shear stress (ISS) distribution along the embedded fibre was obtained.
Xj Xin - One of the best experts on this subject based on the ideXlab platform.
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Prediction of compressive toughness for fibre composites
Proceedings of the Royal Society of London. Series A: Mathematical Physical and Engineering Sciences, 1996Co-Authors: Mpf Sutcliffe, Norman A. Fleck, Xj XinAbstract:The development of microbuckling from a sharp notch under remote compressive loading is analysed for a long fibre composite. The composite is modelled as alternating layers of elastic fibres and a nonlinear Matrix. A finite element analysis is used to predict microbuckle initiation. The relationship between the compressive mode-I stress intensity factor K and the microbuckle length l (that is, the compressive R -curve) is calculated. The effect of Matrix yield Strain on the R -curve is significant, while the influence of the Matrix Strain-hardening rate and initial fibre waviness is slight. R -curves predicted by the finite element method agree qualitatively with those predicted using a cohesive zone model, although there are quantitative differences. Prediction of the initiation of microbuckling is found to be in good agreement with experimental data for a carbon fibre epoxy composite.
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Compressive R-curve of a carbon fibre-epoxy Matrix composite
Composites Part B: Engineering, 1996Co-Authors: Norman A. Fleck, Mpf Sutcliffe, S. Sivashanker, Xj XinAbstract:The development of microbuckling from a sharp notch under remote compressive loading is investigated for a unidirectional carbon-fibre/epoxy composite. Experimental measurements of the overall kink-band width confirm that a growing microbuckle propagates in a crack-like manner rather than like a dislocation. A large-scale bridging model with a crack tip toughness and a constant bridging stress is successful in correlating the length and width of a growing microbuckle with the remote stress. This R-curve behaviour is modelled using a finite element analysis. The effect of Matrix yield Strain on the R-curve is significant, while the influence of the Matrix Strain-hardening rate and initial fibre waviness is slight. Prediction of the initiation of microbuckling is found to be in good agreement with experimental data for a carbon-fibre/ epoxy composite.