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Stephen J. Eichhorn - One of the best experts on this subject based on the ideXlab platform.
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Stress Transfer in microfibrillated cellulose reinforced poly vinyl alcohol composites
Composites Part A-applied Science and Manufacturing, 2014Co-Authors: W W Sampson, Supachok Tanpichai, Stephen J. EichhornAbstract:Abstract Combined homogenisation and sonication treatments of micron-sized lyocell fibres were used to generate microfibrillated cellulose (MFC) with fibril diameters of ∼350 nm. No further reduction in fibril diameter was observed after 30 min treatment. Poly(vinyl alcohol) (PVA) composites reinforced with these fibrils were fabricated using solvent casting and physical and mechanical properties were investigated. The presence of MFC in PVA increased the thermal degradation of the polymer. An increase in both the tensile strength and modulus of the composites was observed for up to 3 wt.% of fibrils; beyond this point no significant increases were observed. An estimate of ∼39 GPa is made for the fibril modulus based on this increase. Stress-Transfer between the polymer resin and the fibrils was investigated using Raman spectroscopy. Stress Transfer in the composite is shown to be greater than that of a pure network of fibres, indicating a good fibre–matrix bond.
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controlling and mapping interfacial Stress Transfer in fragmented hybrid carbon fibre carbon nanotube composites
Composites Science and Technology, 2014Co-Authors: S Y Jin, Robert J Young, Stephen J. EichhornAbstract:Abstract Raman spectroscopy was used to map the Stress Transfer at the interface between high and low modulus carbon fibres in model composites when undergoing fragmentation. Both fibre surfaces were coated with two types of single wall carbon nanotubes (HiPCO and carboxylated nanotubes) in order to enhance the interfacial shear strength with an epoxy resin. For the low modulus carbon fibre this coating also enabled Stress mapping at the interface. In both cases single fibres embedded in a dumbbell shaped model composite were deformed to cause fragmentation. When no further fragmentation took place the critical fibre length was calculated and converted to interfacial shear Stress using classical Kelly–Tyson theory. These values were compared to data obtained using a Raman spectroscopic approach where the rate of change of Stress with respect to distance along the fibre was measured directly. These data were then shown to fit a shear lag model. Two forms of single-wall carbon nanotubes were compared; namely unmodified and COOH modified. It was shown that only the COOH modified single wall carbon nanotubes increase the maximum interfacial shear Stress significantly. Evidence of matrix yielding at the fibre ends is also presented and the possibility of the enhancement of the shear yield Stress of the resin by the presence of the nanotubes is also discussed.
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Stress Transfer in microfibrillated cellulose reinforced poly lactic acid composites using raman spectroscopy
Composites Part A-applied Science and Manufacturing, 2012Co-Authors: Supachok Tanpichai, W W Sampson, Stephen J. EichhornAbstract:Lyocell fibres were used to make microfibrillated cellulose (MFC) by combined homogenisation and sonication. A web-like structure was obtained with fibril diameters in the range of several micrometers to less than 80 nm. Composite samples with PLA resin reinforced with MFC networks were prepared using compression moulding. Young's modulus and tensile strength of these composites increased by similar to 60% and 14% respectively, compared to the pure resin material. Raman spectroscopy was used to monitor the molecular deformation of networks and composite materials. A Raman band initially located at similar to 1095 cm(-1) was observed to shift towards a lower wavenumber position upon tensile deformation. The rate of Raman band shift with respect to strain for the composites was higher than for the pure MFC networks, indicating that the observed improvement in mechanical properties results from Stress Transfer from the PLA resin to the MFC fibrils.
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Stress Transfer in cellulose nanowhisker composites influence of whisker aspect ratio and surface charge
Biomacromolecules, 2011Co-Authors: Rafeadah Rusli, Kadhiravan Shanmuganathan, Stuart J. Rowan, Christoph Weder, Stephen J. EichhornAbstract:The mechanically induced molecular deformation of cellulose nanowhiskers embedded in subpercolation concentration in an epoxy resin matrix was monitored through Raman spectroscopy. Cellulose nanowhiskers isolated by sulfuric acid hydrolysis from tunicates and by sulfuric acid hydrolysis and hydrochloric acid hydrolysis from cotton were used to study how the aspect ratio (ca. 76 for tunicate and 19 for cotton) and surface charges (38 and 85 mmol SO4−/kg for sulfuric acid hydrolysis of cotton and tunicate, respectively; no detectable surface charges for hydrochloric acid hydrolysis) originating from the isolation process influence Stress Transfer in such systems. Atomic force microscopy confirmed that uncharged cellulose nanowhiskers produced by hydrochloric acid hydrolysis have a much higher tendency to aggregate than the charged cotton or tunicate nanowhiskers. Each of these nanowhisker types was incorporated in a concentration of 0.7 vol % in a thermosetting epoxy resin matrix. Mechanically induced shift...
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Stress-Transfer in anisotropic and environmentally adaptive cellulose whisker nanocomposites.
Biomacromolecules, 2010Co-Authors: Rafeadah Rusli, Kadhiravan Shanmuganathan, Stuart J. Rowan, Christoph Weder, Stephen J. EichhornAbstract:Quantitative insights into the Stress-Transfer mechanisms that determine the mechanical properties of tunicate cellulose whisker/poly(vinyl acetate) nanocomposites were gained by Raman spectroscopy. The extent of Stress-Transfer is influenced by local orientation (or anisotropy) of the whiskers, which in turn is governed by the processing conditions used to fabricate the nanocomposites. Solution-cast materials display no microscopic anisotropy, while samples that were cast and subsequently compression molded contain both isotropic regions as well as domains of locally oriented whiskers. Polarized optical microscopy showed these regions to have dimensions in the hundreds of μm. Polarized Raman spectroscopy of the 1095 cm−1 Raman band, associated with C−O ring stretching of the cellulose backbone, was used to quantify the local orientation of the cellulose whiskers. Clear and discernible shifts of this Raman band upon uniaxial deformation of nanocomposite films were further used to determine the level of st...
Robert J Young - One of the best experts on this subject based on the ideXlab platform.
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interfacial and internal Stress Transfer in carbon nanotube based nanocomposites
Journal of Materials Science, 2016Co-Authors: Robert J Young, Libo Deng, Tamer Z Wafy, Ian A KinlochAbstract:This study is concerned with structure–property relationships in different types of carbon nanotubes (CNTs), in particular investigating both interfacial and internal Stress Transfer for CNTs in nanocomposites. The shift of position and width of the G′-Raman band for single-walled CNTs (SWNTs) and multi-walled CNTs (MWNTs) in an epoxy matrix were used to monitor Stress Transfer between the nanotubes and an epoxy matrix in nanocomposites. It was found that the rate of band shift per unit strain was higher for the SWNTs than the MWNTs and that the G′ band tended to undergo broadening with strain for the SWNTs and narrowing with strain for the MWNTs. A theory has been developed to simulate this behaviour in terms of Stress Transfer between the different layers within the MWNTs. It has also enabled the determination of the Stress Transfer efficiency parameter, (k i) for the MWNTs. It is demonstrated that MWNTs give inferior reinforcement to SWNTs as a result of slippage between the walls giving rise to poor internal Stress Transfer in the MWNTs. This phenomenon will lead to the MWNTs having a lower effective Young’s modulus in nanocomposites than SWNTs.
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controlling and mapping interfacial Stress Transfer in fragmented hybrid carbon fibre carbon nanotube composites
Composites Science and Technology, 2014Co-Authors: S Y Jin, Robert J Young, Stephen J. EichhornAbstract:Abstract Raman spectroscopy was used to map the Stress Transfer at the interface between high and low modulus carbon fibres in model composites when undergoing fragmentation. Both fibre surfaces were coated with two types of single wall carbon nanotubes (HiPCO and carboxylated nanotubes) in order to enhance the interfacial shear strength with an epoxy resin. For the low modulus carbon fibre this coating also enabled Stress mapping at the interface. In both cases single fibres embedded in a dumbbell shaped model composite were deformed to cause fragmentation. When no further fragmentation took place the critical fibre length was calculated and converted to interfacial shear Stress using classical Kelly–Tyson theory. These values were compared to data obtained using a Raman spectroscopic approach where the rate of change of Stress with respect to distance along the fibre was measured directly. These data were then shown to fit a shear lag model. Two forms of single-wall carbon nanotubes were compared; namely unmodified and COOH modified. It was shown that only the COOH modified single wall carbon nanotubes increase the maximum interfacial shear Stress significantly. Evidence of matrix yielding at the fibre ends is also presented and the possibility of the enhancement of the shear yield Stress of the resin by the presence of the nanotubes is also discussed.
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interfacial Stress Transfer in graphene oxide nanocomposites
ACS Applied Materials & Interfaces, 2013Co-Authors: Robert J Young, Ian A KinlochAbstract:Raman spectroscopy has been used for the first time to monitor interfacial Stress Transfer in poly(vinyl alcohol) nanocomposites reinforced with graphene oxide (GO). The graphene oxide nanocomposites were prepared by a simple mixing method and casting from aqueous solution. They were characterized using scanning electron microscopy, X-ray diffraction, and polarized Raman spectroscopy and their mechanical properties determined by tensile testing and dynamic mechanical thermal analysis. It was found that GO was fully exfoliated during the nanocomposite preparation process and that the GO nanoplatelets tended align in the plane of the films. The stiffness and yield Stress of the nanocomposites were found to increase with GO loading but the extension to failure decreased. It was shown that the Raman D band at ∼1335 cm–1 downshifted as the nanocomposites were strained as a result of the interfacial Stress Transfer between the polymer matrix and GO reinforcement. From knowledge of the Gruneisen parameter for gr...
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interfacial Stress Transfer in a graphene monolayer nanocomposite
Advanced Materials, 2010Co-Authors: Lei Gong, Robert J Young, Ian A Kinloch, Ibtsam Riaz, R Jalil, Konstantin S NovoselovAbstract:It is demonstrated from Stress-induced Raman bands shifts that Stress can be Transferred from a polymer matrix to a graphene monolayer (see image) in a model nanocomposite. It is shown further that the behavior can be modeled using continuum mechanics and that the interface between the graphene and the polymer breaks down at a shear Stress of the order of 2 MPa.
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The effect of Stress Transfer within double-walled carbon nanotubes upon their ability to reinforce composites
Advanced Materials, 2009Co-Authors: Shuang Cui, Robert J Young, Iann Kinloch, Laure Noé, Marc MonthiouxAbstract:The effect of Stress Transfer within double-walled carbon nanotubes upon their ability to reinforce composites has been reported. The level to which Stress can be Transferred between the different layers or walls in multiwalled carbon nanotubes (MWNT) is of profound significance for their ability to reinforce a matrix. The double multiwalled carbon nanotubes (DWNT) samples were prepared starting from commercial SWNT materials prepared via the electric-arc method (NANOCARBLAB). It has been found that the Stress Transfer from the outer to the inner walls in DWNT in composites is poor, such that the inner walls are virtually unStressed during both tensile and compressive deformation. The implication of this finding is that the effective Young's Modulus MWNT in composites will be relatively low. The pressurization involves only the hydrostatic component of the Stress tensor, which deforms both the inner and outer walls equally.
L.n. Mccartney - One of the best experts on this subject based on the ideXlab platform.
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theory of variational Stress Transfer in general symmetric composite laminates containing non uniformly spaced ply cracks
Composites Part A-applied Science and Manufacturing, 2018Co-Authors: Mohammad Hajikazemi, L.n. Mccartney, W Van Paepegem, M H SadrAbstract:Abstract Ply cracking is an inherently stochastic process due to the random variability of local material properties of the plies. Such randomness in microstructure and in failure evolution generally leads to non-uniform distributions of ply cracks. Modeling this non-uniformity is a crucial factor in predicting the initiation and propagation of matrix cracks. Therefore, a novel Stress-based variational model is developed to accurately predict Stress Transfer and stiffness reduction in general symmetric laminates containing non-uniformly spaced ply cracks. In contrast to available approaches for uniformly spaced ply cracks based on the unit cell, the analysis is carried out for the entire laminate. Results derived from the developed method for thermo-elastic properties of the cracked laminates show an excellent agreement with finite element results. Moreover, the accuracy of predictions based on an approximate approach is discussed using a comprehensive analysis of various laminates and crack patterns for both carbon and glass fibre systems.
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theory of Stress Transfer in a 0 90 0 cross ply laminate containing a parallel array of transverse cracks
Journal of The Mechanics and Physics of Solids, 1992Co-Authors: L.n. MccartneyAbstract:Abstract Two new analytical methods have been developed that can predict the Stress Transfer between the 0 and 90° plies in a 0°—90°—0° cross-ply laminate containing transverse cracks. Account is taken of thermal residual Stresses arising from a mismatch in thermal expansion coefficients of the 0 and 90° plies. The first method is based on a 2-D model which assumes that generalised plane strain conditions prevail. The theoretical approach retains all relevant Stress and displacement components, and satisfies exactly the equilibrium equations, the interface conditions, and other boundary conditions involving Stresses. The Stress—strain—temperature relations are satisfied either exactly or in an average sense. The 2-D representation can be used to predict the Stress and displacement fields for a laminate containing parallel transverse cracks. In this paper the solutions are used to estimate the dependence of the longitudinal values of Young's modulus, Poisson's ratio, and thermal expansion coefficient on the density of transverse cracks. The second analytical method extends the 2-D model so that it can apply to 3-D problems which arise, for example, when edge effects or orthogonal cracking are to be taken into account. For the special case of very large laminate widths the 2- and 3-D models predict results which are very close to each other for both glass fibre/epoxy and carbon fibre/epoxy laminates. It is shown how the 3-D model can be used to predict the transverse Young's modulus and thermal expansion coefficient. Theoretical predictions of the dependence of Poisson's ratio on transverse crack density indicate that experimental measurements can be sensitive to the strain measurement technique used, and to specimen width when using a transverse extensometer. Theoretical predictions, for glass fibre/epoxy and carbon fibre/epoxy laminates, of the dependence of Young's modulus and Poisson's ratio on the crack density are compared with some experimental results.
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analytical models of Stress Transfer in unidirectional composites and cross ply laminates and their application to the prediction of matrix transverse cracking
1992Co-Authors: L.n. MccartneyAbstract:Many unidirectional composites are made using carbon fibres which have anisotropic thermo-mechanical properties. There is a need, therefore, to take account of this anisotropy when making predictions of the properties of damaged composites. For the more general case when the fibres and matrix are both transverse isotropic solids, a relatively simple shear-lag approach to understanding Stress Transfer between fibres and matrix is presented. A similar approach is used to develop a shear-lag model of Stress Transfer between neighbouring plies in a cross-ply laminate containing transverse cracks. As to be expected Stress Transfer is governed by second order ordinary differential equations which are easily solved. It is shown how a more realistic model of Stress Transfer for unidirectional composites must be modified when the fibres and matrix of the composite are transverse isotropic solids. Reference is made to more realistic models of Stress Transfer in cross-ply laminates containing transverse cracks in the 90 ply. The more realistic models lead to fourth order differential equations. Such models are thus more flexible than shear lag models in that a greater variety of boundary conditions can be satisfied.
Rafeadah Rusli - One of the best experts on this subject based on the ideXlab platform.
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Stress Transfer in cellulose nanowhisker composites influence of whisker aspect ratio and surface charge
Biomacromolecules, 2011Co-Authors: Rafeadah Rusli, Kadhiravan Shanmuganathan, Stuart J. Rowan, Christoph Weder, Stephen J. EichhornAbstract:The mechanically induced molecular deformation of cellulose nanowhiskers embedded in subpercolation concentration in an epoxy resin matrix was monitored through Raman spectroscopy. Cellulose nanowhiskers isolated by sulfuric acid hydrolysis from tunicates and by sulfuric acid hydrolysis and hydrochloric acid hydrolysis from cotton were used to study how the aspect ratio (ca. 76 for tunicate and 19 for cotton) and surface charges (38 and 85 mmol SO4−/kg for sulfuric acid hydrolysis of cotton and tunicate, respectively; no detectable surface charges for hydrochloric acid hydrolysis) originating from the isolation process influence Stress Transfer in such systems. Atomic force microscopy confirmed that uncharged cellulose nanowhiskers produced by hydrochloric acid hydrolysis have a much higher tendency to aggregate than the charged cotton or tunicate nanowhiskers. Each of these nanowhisker types was incorporated in a concentration of 0.7 vol % in a thermosetting epoxy resin matrix. Mechanically induced shift...
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Stress-Transfer in anisotropic and environmentally adaptive cellulose whisker nanocomposites.
Biomacromolecules, 2010Co-Authors: Rafeadah Rusli, Kadhiravan Shanmuganathan, Stuart J. Rowan, Christoph Weder, Stephen J. EichhornAbstract:Quantitative insights into the Stress-Transfer mechanisms that determine the mechanical properties of tunicate cellulose whisker/poly(vinyl acetate) nanocomposites were gained by Raman spectroscopy. The extent of Stress-Transfer is influenced by local orientation (or anisotropy) of the whiskers, which in turn is governed by the processing conditions used to fabricate the nanocomposites. Solution-cast materials display no microscopic anisotropy, while samples that were cast and subsequently compression molded contain both isotropic regions as well as domains of locally oriented whiskers. Polarized optical microscopy showed these regions to have dimensions in the hundreds of μm. Polarized Raman spectroscopy of the 1095 cm−1 Raman band, associated with C−O ring stretching of the cellulose backbone, was used to quantify the local orientation of the cellulose whiskers. Clear and discernible shifts of this Raman band upon uniaxial deformation of nanocomposite films were further used to determine the level of st...
S A Hayes - One of the best experts on this subject based on the ideXlab platform.
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the role of matrix cracks and fibre matrix debonding on the Stress Transfer between fibre and matrix in a single fibre fragmentation test
Composites Part A-applied Science and Manufacturing, 2012Co-Authors: Anbu Clemensis Johnson, S A HayesAbstract:The single fibre fragmentation test is commonly used to characterise the fibre/matrix interface. During fragmentation, the stored energy is released resulting in matrix cracking and/or fibre/matrix debonding. Axisymmetric finite element models were formulated to study the impact of matrix cracks and fibre/matrix debonding on the effective Stress Transfer efficiency (EST) and Stress Transfer length (STL). At high strains, plastic deformation in the matrix dominated the Stress Transfer mechanism. The combination of matrix cracking and plasticity reduced the EST and increased STL. For experimental validation, three resins were formulated and the fragmentation of an unsized and uncoupled E-glass fibre examined as a function of matrix properties. Fibre failure was always accompanied by matrix cracking and debonding. With the stiff resin, debonding, transverse matrix cracking and conical crack initiation were observed. With a lower modulus and lower yield strength resin the transverse matrix crack length decreased while that of the conical crack increased.
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influence of a matrix crack on Stress Transfer to an α alumina fibre in epoxy resin using fea and photoelasticity
Composites Science and Technology, 2006Co-Authors: Anbu Clemensis Johnson, F.m. Zhao, S A Hayes, F R JonesAbstract:Abstract Elasto-plastic finite element analysis was used to investigate the influence of a transverse matrix crack on the matrix Stress Transfer to an isolated alumina fibre in epoxy resin. With an increase in transverse crack length perpendicular to the fibre the Stress Transfer length of the fibre (STL) increased, thereby reducing its reinforcing efficiency. The maximum shear Stress at the fibre/matrix interface was found to be displaced away from the fibre-break. Phase-stepping automated photoelasticity was used to quantify the Stress field surrounding the broken fibre in the presence of a transverse matrix crack which had propagated into the epoxy resin matrix. The interfacial shear Stress was calculated from these Stress fields and compared with the finite element analysis. A reasonable agreement was obtained. The maxima in the shear Stress plot observed in the FEA calculations were also observed in the photoelasticity results.
