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Costas Galiotis - One of the best experts on this subject based on the ideXlab platform.
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Viscoplastic finite element analysis of matrix crack propagation in model continuous-carbon Fibre/epoxy composites
Composites Part A: Applied Science and Manufacturing, 2006Co-Authors: S Sirivedin, D.n. Fenner, R B Nath, Costas GaliotisAbstract:Abstract Non-linear finite element (FE) analysis was used to investigate the effect of matrix viscoplasticity in a continuous carbon Fibre/epoxy composite subject to tensile loading. During Fibre fracture, the sudden increase in the strain rate near the fracture location reduces matrix ductility which results in catastrophic failure involving rapid matrix crack-growth. By applying the minimum strain energy density criterion to the FE results, the semi-cone angle of a matrix crack was predicted to be in the range 32°–36°, twice the value for the corresponding short Fibre system. The FE results were compared with experimental results obtained from laser Raman spectroscopy (LRS), and it was found that the Fibre Stress profiles are characteristic of conical matrix crack geometries. Good correlation was observed with the experimental results confirming matrix cracking as the primary mode of failure for this composite system. The energy balance model was used to determine the available strain energy to propagate the crack.
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Effects of inter-Fibre spacing and matrix cracks on Stress amplification factors in carbon-Fibre/epoxy matrix composites. Part I: planar array of Fibres
Composites Part A-applied Science and Manufacturing, 2003Co-Authors: S Sirivedin, D.n. Fenner, R B Nath, Costas GaliotisAbstract:When the loading on a composite is sufficient to cause fracture of an individual Fibre, the resulting Stress amplification in the adjacent intact Fibres may be large enough to cause failure of these Fibres. In this work, 3D elasto-plastic finite element analysis was used to investigate the effect of inter-Fibre spacing on the Stress amplification factor in a composite comprising a planar array of Fibres. A Progressional Approach was used in the FE analysis to simulate the constituent non-linear processes associated with the generation of thermal residual Stresses from fabrication, the Fibre fracture event and the subsequent initiation and propagation of conical matrix cracks induced with incremental tensile loading. As the inter-Fibre spacing increases, the effect of Fibre fracture on the Stress distribution in the neighbouring intact Fibres is reduced, whereas the effect on the matrix material is increased, thereby inducing localised yielding. The presence of a conical-shaped matrix crack was found to increase both the Stress amplification factor and the positively affected length in neighbouring Fibres. For a large inter-Fibre spacing, a longer matrix crack is required to obtain good agreement with LRS measurements of Fibre Stress.
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The progressional approach to interfacial failure in carbon reinforced composites: elasto-plastic finite element modelling of interface cracks
Composites Part A: Applied Science and Manufacturing, 2000Co-Authors: R B Nath, D.n. Fenner, Costas GaliotisAbstract:Abstract A rigorous stage-by-stage ‘Progressional Approach’ to interfacial failure is described in which elasto-plastic finite element (FE) analysis has been used to model the initiation and subsequent propagation of an interface crack in a tensile loaded single carbon Fibre composite specimen. The non-linear effects of frictional Stress transfer across the debonded interface and the residual Stresses thermally induced due to curing have been included. Such effects were found to play a key role in determining the reinforcement efficiency of the Fibre as failure at the interface progressed, during incremental loading. Previously published laser Raman spectroscopy measurements for Fibre Stress distributions have been compared with the FE predictions, for a number of Stress levels in the composite. Good correlation was obtained with the experimental data, for a number of interface crack lengths and for a coefficient of friction 0.8–0.9 at the cracked interface. The Fibre Stress distributions obtained were found to be characteristic of this mode of interfacial failure.
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Surface and bulk Stress/strain measurements in composite laminates with a Fibre-optic Raman probe
Composites Part A: Applied Science and Manufacturing, 1999Co-Authors: Bish Arjyal, P.a. Tarantili, A. G. Andreopoulos, Costas GaliotisAbstract:Fibre Stress/strain measurements in unidirectional, as well as, multidirectional aramid/epoxy composites have been conducted with the use of a laser Raman microprobe. The composite was incrementally loaded in tension while Raman measurements were taken. Fibre-optic probes sandwiched between adjacent laminae were employed for channelling the laser excitation light to a specified location within the bulk of the composite. The direction of the Fibre-optic was either perpendicular or parallel to the reinforcing Fibres. For comparison purposes, the same Fibre-optic probe was used to scan the surface of the laminates. The perpendicular configuration was found to reduce the tensile strength of the as-received composite coupon by 10% whereas the parallel second configuration had no effect. In the unidirectional coupons the Stress or strain in the principal Fibre direction could be measured prior to loading and at every increment of applied tensile load up to fracture. The take-up of Fibre strain for both bulk and surface set of measurements was identical with that obtained from the attached electrical resistance strain gauges. In the case of multidirectional coupons the Stress or strain in the principal direction could be measured within successive plies situated at angles θ to the loading direction. The results for the 0° plies were in good agreement with those obtained by conventional laminate analysis whereas small deviations from linearity were observed in the angle plies. The proposed methodology paves the way for simultaneous in-service Stress/strain measurements on the reinforcing Fibres situated on the surface or within the bulk of a composite laminate.
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Effects of interface, volume fraction and geometry on Stress redistribution in polymer composites under tension
Composites Science and Technology, 1997Co-Authors: Varinder Chohan, Costas GaliotisAbstract:Abstract The interfacial and fracture characteristics of highmodulus carbon-Fibre/epoxy-resin composites have been investigated. Three different coupon geometries were employed, namely 2D microcomposite tapes, Fibre tows and full composite tensile coupons. In all cases, the point-by-point Stress in the Fibre was measured by the technique of remote laser Raman microscopy (ReRaM). The composite specimens were loaded incrementally in tension and the Stress transfer profiles emanating from the Fibre, were closely monitored. At each applied Stress level, the interfacial shear Stress (ISS) distribution was derived by means of a balance of shear-to-axial forces argument. The redistribution of Stress in Fibres adjacent to a filament break in all geometries was determined as a function of distance from the Fibre fracture. The values of Stress concentration were found to depend upon the number of nearest neighbours and the radial distance from the Fibre fracture. Thus, the apparent discrepancy between measurements obtained from 2D tapes and those from full unidirectional composites was resolved. A phenomenological equation was derived to relate the Fibre Stress concentration to interFibre distance for both geometries. This equation has also been employed to estimate the Stress concentration in the bulk of a composite for a hexagonal array of Fibres. Finally, the interfacial shear Stress in the neighbouring Fibres as a result of the shear perturbation induced by an adjacent Fibre fracture has been quantified for the first time.
Andreas Mortensen - One of the best experts on this subject based on the ideXlab platform.
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The influence of non-linear elasticity on the determination of Weibull parameters using the Fibre bundle tensile test
Composites Part A: Applied Science and Manufacturing, 2003Co-Authors: B. Moser, Ludger Weber, A. Rossoll, Andreas MortensenAbstract:We address the influence of individual Fibre Stress‐ strain non-linearity on the extraction of Weibull-parameters from Fibre bundle tensile tests. We extend the statistical theory of Fibre bundle strength to include the non-linear elastic behaviour observed in many technically important Fibres, e.g. glass-, carbon-, and alumina-Fibres. It is shown that neglecting this non-linearity may lead to significant errors in determining the shape and scale parameters of the Fibre fracture strength Weibull-distribution. A refinement of the existing extraction technique, accounting for this effect, is presented. The error resulting from neglecting the non-linear behaviour is assessed through a parametric study of the Weibull parameters for different levels of non-linearity. Explicit calculations are performed for two Fibres of technical importance, namely Nextel 610e a-alumina Fibre and a T300 carbon Fibre. q 2003 Elsevier Ltd. All rights reserved.
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The influence of non-linear elasticity on the determination of Weibull parameters using the Fibre bundle tensile test
Composites Part A: Applied Science and Manufacturing, 2003Co-Authors: B. Moser, Ludger Weber, A. Rossoll, Andreas MortensenAbstract:Abstract We address the influence of individual Fibre Stress–strain non-linearity on the extraction of Weibull-parameters from Fibre bundle tensile tests. We extend the statistical theory of Fibre bundle strength to include the non-linear elastic behaviour observed in many technically important Fibres, e.g. glass-, carbon-, and alumina-Fibres. It is shown that neglecting this non-linearity may lead to significant errors in determining the shape and scale parameters of the Fibre fracture strength Weibull-distribution. A refinement of the existing extraction technique, accounting for this effect, is presented. The error resulting from neglecting the non-linear behaviour is assessed through a parametric study of the Weibull parameters for different levels of non-linearity. Explicit calculations are performed for two Fibres of technical importance, namely Nextel 610™ α-alumina Fibre and a T300 carbon Fibre.
S. J. Eichhorn - One of the best experts on this subject based on the ideXlab platform.
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Analysis of interfacial micromechanics of model composites using synchrotron microfocus X-ray diffraction
Journal of Materials Science, 2006Co-Authors: Y. T. Shyng, J.a. Bennett, R. J. Young, R. J. Davies, S. J. EichhornAbstract:The deformation micromechanics of single-Fibre embedded model composites of poly( p -phenylene benzobisoxazole) (PBO) and poly( p -phenylene terephthalamide) (PPTA) Fibres, embedded in an epoxy resin have been examined using synchrotron microfocus X-ray diffraction. Single Fibres (in air) were deformed and the c- spacing monitored to establish a calibration of crystal strain against applied Stress. Subsequently, the variation in crystal strain along Fibres, embedded in the resin matrix was mapped using synchrotron microfocus X-ray diffraction. Raman spectroscopy was then used to map molecular deformation on the same samples (recorded as shifts in the Raman band wavenumber) in order to provide a complementary Stress data. A shear-lag analysis was conducted on the axial Fibre Stress data in order to calculate interfacial shear Stress and identify different Stress-transfer modes at Fibre/resin interfaces. The results establish that the axial Fibre Stress distributions measured by synchrotron microfocus X-ray diffraction correlate well with those obtained using Raman spectroscopy. The interfacial shear Stress data derived from the Stress-transfer profiles also show a good degree of correlation.
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Analysis of interfacial micromechanics in microdroplet model composites using synchrotron microfocus X-ray diffraction
Composites Science and Technology, 2006Co-Authors: S. J. Eichhorn, R. J. Young, J.a. Bennett, Y. T. Shyng, R. J. DaviesAbstract:Microfocus X-ray diffraction, a synchrotron radiation based technique, has been used to determine the Fibre/matrix interfacial shear Stress within a new type of model composite. This model composite comprises a single Fibre of poly(p-phenylene terephthalamide) or poly(p-phenylene benzobisoxazole) with an epoxy resin microdroplet attached along its length. Shifts of meridional Bragg peaks as a function of Stress have been determined for each Fibre type and used as a calibration of Fibre Stress both inside and outside of the droplets. The variation of Stress was mapped along the Fibre in the microdroplet composites at different levels of applied Stress. A modified single Fibre pull-out shear lag analysis with an interfacial failure criterion was used to interpret the data. The microdroplet geometry, which is similar to the more established microbond test has several advantages; the primary advantage is that there is no need for a mechanical restraint on the droplet, as in a microbond test.
B. Moser - One of the best experts on this subject based on the ideXlab platform.
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The influence of non-linear elasticity on the determination of Weibull parameters using the Fibre bundle tensile test
Composites Part A: Applied Science and Manufacturing, 2003Co-Authors: B. Moser, Ludger Weber, A. Rossoll, Andreas MortensenAbstract:We address the influence of individual Fibre Stress‐ strain non-linearity on the extraction of Weibull-parameters from Fibre bundle tensile tests. We extend the statistical theory of Fibre bundle strength to include the non-linear elastic behaviour observed in many technically important Fibres, e.g. glass-, carbon-, and alumina-Fibres. It is shown that neglecting this non-linearity may lead to significant errors in determining the shape and scale parameters of the Fibre fracture strength Weibull-distribution. A refinement of the existing extraction technique, accounting for this effect, is presented. The error resulting from neglecting the non-linear behaviour is assessed through a parametric study of the Weibull parameters for different levels of non-linearity. Explicit calculations are performed for two Fibres of technical importance, namely Nextel 610e a-alumina Fibre and a T300 carbon Fibre. q 2003 Elsevier Ltd. All rights reserved.
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The influence of non-linear elasticity on the determination of Weibull parameters using the Fibre bundle tensile test
Composites Part A: Applied Science and Manufacturing, 2003Co-Authors: B. Moser, Ludger Weber, A. Rossoll, Andreas MortensenAbstract:Abstract We address the influence of individual Fibre Stress–strain non-linearity on the extraction of Weibull-parameters from Fibre bundle tensile tests. We extend the statistical theory of Fibre bundle strength to include the non-linear elastic behaviour observed in many technically important Fibres, e.g. glass-, carbon-, and alumina-Fibres. It is shown that neglecting this non-linearity may lead to significant errors in determining the shape and scale parameters of the Fibre fracture strength Weibull-distribution. A refinement of the existing extraction technique, accounting for this effect, is presented. The error resulting from neglecting the non-linear behaviour is assessed through a parametric study of the Weibull parameters for different levels of non-linearity. Explicit calculations are performed for two Fibres of technical importance, namely Nextel 610™ α-alumina Fibre and a T300 carbon Fibre.
R. J. Young - One of the best experts on this subject based on the ideXlab platform.
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Tensile failure phenomena in carbon Fibres
Carbon, 2016Co-Authors: Haruki Okuda, R. J. Young, Fumihiko Tanaka, Jun Watanabe, Tomonaga OkabeAbstract:Abstract In order to clarify the effect of nanostructure upon the tensile strength of polyacrylonitrile (PAN)-based carbon Fibres, experimental as well as theoretical studies have been performed. A new technique for the quantitative evaluation of the high strength region has been developed by combining the loop test with Raman spectroscopic measurements to overcome uncertainties in Fibre Stress, which have been the major drawback of the conventional loop test. The tensile strength at gauge lengths of a few tens of μm was successfully evaluated and a tensile strength as high as 13 GPa was observed experimentally for commercially-available PAN-based carbon Fibres, showing their potential high tensile strengths. The strength distributions were found to be highly uniform in the high strength region, represented by Weibull shape parameters of ∼20. A tensile strength model that can reasonably account for the effect of the nanostructures has been proposed, suggesting there is considerable scope for further improvements in the tensile strength of PAN-based carbon Fibres.
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Analysis of interfacial micromechanics in microdroplet model composites using synchrotron microfocus X-ray diffraction
Composites Science and Technology, 2006Co-Authors: S. J. Eichhorn, R. J. Young, J.a. Bennett, Y. T. Shyng, R. J. DaviesAbstract:Microfocus X-ray diffraction, a synchrotron radiation based technique, has been used to determine the Fibre/matrix interfacial shear Stress within a new type of model composite. This model composite comprises a single Fibre of poly(p-phenylene terephthalamide) or poly(p-phenylene benzobisoxazole) with an epoxy resin microdroplet attached along its length. Shifts of meridional Bragg peaks as a function of Stress have been determined for each Fibre type and used as a calibration of Fibre Stress both inside and outside of the droplets. The variation of Stress was mapped along the Fibre in the microdroplet composites at different levels of applied Stress. A modified single Fibre pull-out shear lag analysis with an interfacial failure criterion was used to interpret the data. The microdroplet geometry, which is similar to the more established microbond test has several advantages; the primary advantage is that there is no need for a mechanical restraint on the droplet, as in a microbond test.
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Photoelastic analysis of matrix Stresses around a high modulus sapphire Fibre by means of phase-stepping automated polariscope
Composites Part A-applied Science and Manufacturing, 2004Co-Authors: F.m. Zhao, R. J. Young, R.d.s. Martin, Simon A. Hayes, Eann A. Patterson, Frank R. JonesAbstract:Abstract The matrix Stress field has been quantified and the micromechanics of fragmentation of sapphire Fibres in an epoxy matrix have been investigated using phase-stepping photoelasticity and fluorescence spectroscopy. Contour maps of the isochromatic fringe order (related to the difference in principal Stresses) have been used to describe in detail the changes in matrix Stress field during Stress transfer in the presence of a matrix crack and interfacial debonding. The profiles of interfacial shear Stress at various levels of applied matrix Stress indicate clearly the extent of interfacial debonding. The results show that the matrix crack significantly reduces the efficiency of Stress transfer at the interface. The frictional shear Stress at the debonded interface has been found experimentally to be 3–10 MPa for a sapphire Fibre embedded in the LY5052/HY5052 epoxy system. The relationship between interfacial shear Stress and axial Fibre Stress is discussed. The interfacial shear Stress profiles obtained from photoelasticity has been compared to that calculated from the axial Fibre Stress measured by shifts in fluorescence spectral bands.
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Determination of the axial and radial Fibre Stress distributions for the Broutman test
Composites Science and Technology, 2004Co-Authors: R. Sinclair, R. J. Young, R.d.s. MartinAbstract:Composite micromechanics has been a subject of considerable interest over the past 25 years. Most research has been concerned with single-Fibre composite specimens and the distribution of axial Fibre Stress or strain. The main parameter of interest is normally the interfacial shear Stress that characterises the conditions for the breakdown of the Fibre/matrix interface. Over recent years significant advances have been made through the use of Raman and/or fluorescence microscopy to map the distribution of axial Stress and strain along the Fibres. This paper reports the development of fluorescence microscopy to enable both axial and radial Fibre Stresses to be determined in alumina single crystal Fibres embedded in epoxy resins. This is demonstrated for the Broutman test in which the Fibre/matrix interface is subjected to significant levels of transverse radial Stress. The micromechanics of reinforcement by single crystal and polycrystalline alumina Fibres is contrasted. Important new insights into the processes that initiate breakdown of the Fibre/matrix interface are evaluated.
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Compressive behaviour of rigid rod polymer Fibres and their adhesion to composite matrixes
Plastics Rubber and Composites, 2003Co-Authors: C. L. So, J.a. Bennett, J. Sirichaisit, R. J. YoungAbstract:AbstractThe deformation behaviour of the new high performance polymer Fibres, poly(p-phenylene benzobisoxazole) (PBO) and polypyridobisimidazole (PIPD) and their adhesion to an epoxy composite matrix have been investigated. Both Fibres give well defined Raman spectra, and the deformation micromechanics of PBO and PIPD single Fibres and composites were studied from Stress induced Raman band shifts. Single Fibre Stress-strain curves were determined in both tension and compression, thus providing an estimate of the compressive strength of these Fibres. It was found that the PIPD Fibre has a higher compressive strength (~1 GPa) than PBO (~0·3 GPa) and other high performance polymer Fibres, because hydrogen bond formation is possible between PIPD molecules. It has been shown that when PBO and PIPD Fibres are incorporated into an epoxy resin matrix, the resulting composites show very different interfacial failure mechanisms. The Fibre strain distribution in the PBO-epoxy composites follows that predicted by the...