The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform
Anthony Bunsell - One of the best experts on this subject based on the ideXlab platform.
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Effect of input properties on the predicted failure of a composite pressure vessel using a multiscale model
2019Co-Authors: Martinus Widjaja, Anthony Bunsell, Sébastien Joannès, Faisal Islam, G. Mair, Alain ThionnetAbstract:A multiscale Fibre Break model (FBM) developed at Mines ParisTech has shown relatively good comparison to the experimental observations by computed tomography (CT) technique, however, it was mentioned that a better description of T700 Fibre properties is necessary as it may affect the accumulation process of the Fibre Breaks. Therefore, further study on Fibre strength characterisation can provide insights on the actual Fibre strength variation and thereby also improve the quality of the failure predictions of the FBM. In this paper, an attempt has been made to understand the variability in the predicted failure of CPVs using the FBM, as a result of the expected variability in the input Fibre properties.
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Defining a reduced volume zone for the simulation of burst test on a composite pressure vessels
2018Co-Authors: Martinus P. Widjaja, Anthony Bunsell, Sébastien Joannès, G. Mair, Alain ThionnetAbstract:A Fibre-Break Model (FBM) developed at Mines ParisTech can predict the burst pressure of high pressure composite vessels. This model uses random values of Fibre strength at each Gauss point of the considered vessels meshed with finite element (FE). However, previous studies has determined the optimum FEs to be used on real-scale structures (0.1 mm x 0.1 mm x 8 mm). A simple calculation shows that, on a real-scale pressure vessel, this induces a gigantic number of FEs, hence the extensive computation time. To overcome this problem, the integral range method is proposed to find a reduced volume zone of the vessels, on which an equivalent calculation can be made and gives the same results with the one that employs the FBM on the entire structure.
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Benchmarking of strength models for unidirectional composites under longitudinal tension
Composites Part A: Applied Science and Manufacturing, 2018Co-Authors: Anthony Bunsell, Ian Sinclair, Yentl Swolfs, Larissa Gorbatikh, Hannah Morton, Soraia Pimenta, Mark Spearing, Alain ThionnetAbstract:Several modelling approaches are available in the literature to predict longitudinal tensile failure of Fibre-reinforced polymers. However, a systematic, blind and unbiased comparison between the predictions from the different models and against experimental data has never been performed. This paper presents a benchmarking exercise performed for three different models from the literature: (i) an analytical hierarchical scaling law for composite Fibre bundles, (ii) direct numerical simulations of composite Fibre bundles, and (iii) a multiscale finite-element simulation method. The results show that there are significant discrepancies between the predictions of the different modelling approaches for Fibre-Break density evolution, cluster formation and ultimate strength, and that each of the three models presents unique advantages over the others. Blind model predictions are also compared against detailed computed-tomography experiments, showing that our understanding of the micromechanics of longitudinal tensile failure of composites needs to be developed further.
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The application of a reduced volume method for the simulation of the characterisation of a carbon Fibre pressure vessel
2018Co-Authors: Martinus P. Widjaja, Anthony Bunsell, Sébastien Joannès, Georg Mair, Alain ThionnetAbstract:The characteristics of advanced composite materials make them ideally suited for use in pressure vessels for storing gas as fuel for ground transport vehicles. It has been found that the failure process starts with randomly distributed Fibre Breaks and as the loading continues, they coalesce into clusters of Fibre Breaks which lead to failure [4]. However, improvements are needed to reduce computational times when performing full-scale simulations. The reduced volume method is therefore applied to the stochastic Fibre Break model related to the concept of an integral range. This method allows the calculation for a certain volume of a laminate that statistically represents the same physical properties as a full-scale pressure vessel. A convergence study with multiple configurations has been done and shows that the assignment of Fibre failure strength values at each integration points is not the same if the related configurations were rotated. The integral method has been successfully applied to the 3D case and by using only 23 elements for 1 simulation, 95% of confidence level can be achieved. Another important remark is that the result from the model is highly sensitive with the Weibull characteristics value that was used to produce the Fibre rupture values.
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Fibre Break failure processes in unidirectional composites: evaluation of critical damage states.
Philosophical transactions. Series A Mathematical physical and engineering sciences, 2016Co-Authors: Alain Thionnet, Anthony BunsellAbstract:Earlier work which successfully modelled the kinetics of Fibre Breakage in unidirectional composites under monotonic tensile loading has been extended to quantify the kinetics of Fibre failure during both monotonic and sustained tensile loading. In both cases, failure was seen to occur when a critical density of large clusters (more than 16 Fibres are broken within the representative volume element) of Fibre Breaks developed. However, in monotonic loading failure occurred very quickly after the first development of these large clusters, whereas under sustained loading the composite could accommodate greater levels of large clusters because of the lower applied load. This article is part of the themed issue 'Multiscale modelling of the structural integrity of composite materials'.
Alain Thionnet - One of the best experts on this subject based on the ideXlab platform.
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Effect of input properties on the predicted failure of a composite pressure vessel using a multiscale model
2019Co-Authors: Martinus Widjaja, Anthony Bunsell, Sébastien Joannès, Faisal Islam, G. Mair, Alain ThionnetAbstract:A multiscale Fibre Break model (FBM) developed at Mines ParisTech has shown relatively good comparison to the experimental observations by computed tomography (CT) technique, however, it was mentioned that a better description of T700 Fibre properties is necessary as it may affect the accumulation process of the Fibre Breaks. Therefore, further study on Fibre strength characterisation can provide insights on the actual Fibre strength variation and thereby also improve the quality of the failure predictions of the FBM. In this paper, an attempt has been made to understand the variability in the predicted failure of CPVs using the FBM, as a result of the expected variability in the input Fibre properties.
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Defining a reduced volume zone for the simulation of burst test on a composite pressure vessels
2018Co-Authors: Martinus P. Widjaja, Anthony Bunsell, Sébastien Joannès, G. Mair, Alain ThionnetAbstract:A Fibre-Break Model (FBM) developed at Mines ParisTech can predict the burst pressure of high pressure composite vessels. This model uses random values of Fibre strength at each Gauss point of the considered vessels meshed with finite element (FE). However, previous studies has determined the optimum FEs to be used on real-scale structures (0.1 mm x 0.1 mm x 8 mm). A simple calculation shows that, on a real-scale pressure vessel, this induces a gigantic number of FEs, hence the extensive computation time. To overcome this problem, the integral range method is proposed to find a reduced volume zone of the vessels, on which an equivalent calculation can be made and gives the same results with the one that employs the FBM on the entire structure.
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Benchmarking of strength models for unidirectional composites under longitudinal tension
Composites Part A: Applied Science and Manufacturing, 2018Co-Authors: Anthony Bunsell, Ian Sinclair, Yentl Swolfs, Larissa Gorbatikh, Hannah Morton, Soraia Pimenta, Mark Spearing, Alain ThionnetAbstract:Several modelling approaches are available in the literature to predict longitudinal tensile failure of Fibre-reinforced polymers. However, a systematic, blind and unbiased comparison between the predictions from the different models and against experimental data has never been performed. This paper presents a benchmarking exercise performed for three different models from the literature: (i) an analytical hierarchical scaling law for composite Fibre bundles, (ii) direct numerical simulations of composite Fibre bundles, and (iii) a multiscale finite-element simulation method. The results show that there are significant discrepancies between the predictions of the different modelling approaches for Fibre-Break density evolution, cluster formation and ultimate strength, and that each of the three models presents unique advantages over the others. Blind model predictions are also compared against detailed computed-tomography experiments, showing that our understanding of the micromechanics of longitudinal tensile failure of composites needs to be developed further.
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The application of a reduced volume method for the simulation of the characterisation of a carbon Fibre pressure vessel
2018Co-Authors: Martinus P. Widjaja, Anthony Bunsell, Sébastien Joannès, Georg Mair, Alain ThionnetAbstract:The characteristics of advanced composite materials make them ideally suited for use in pressure vessels for storing gas as fuel for ground transport vehicles. It has been found that the failure process starts with randomly distributed Fibre Breaks and as the loading continues, they coalesce into clusters of Fibre Breaks which lead to failure [4]. However, improvements are needed to reduce computational times when performing full-scale simulations. The reduced volume method is therefore applied to the stochastic Fibre Break model related to the concept of an integral range. This method allows the calculation for a certain volume of a laminate that statistically represents the same physical properties as a full-scale pressure vessel. A convergence study with multiple configurations has been done and shows that the assignment of Fibre failure strength values at each integration points is not the same if the related configurations were rotated. The integral method has been successfully applied to the 3D case and by using only 23 elements for 1 simulation, 95% of confidence level can be achieved. Another important remark is that the result from the model is highly sensitive with the Weibull characteristics value that was used to produce the Fibre rupture values.
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Fibre Break failure processes in unidirectional composites: evaluation of critical damage states.
Philosophical transactions. Series A Mathematical physical and engineering sciences, 2016Co-Authors: Alain Thionnet, Anthony BunsellAbstract:Earlier work which successfully modelled the kinetics of Fibre Breakage in unidirectional composites under monotonic tensile loading has been extended to quantify the kinetics of Fibre failure during both monotonic and sustained tensile loading. In both cases, failure was seen to occur when a critical density of large clusters (more than 16 Fibres are broken within the representative volume element) of Fibre Breaks developed. However, in monotonic loading failure occurred very quickly after the first development of these large clusters, whereas under sustained loading the composite could accommodate greater levels of large clusters because of the lower applied load. This article is part of the themed issue 'Multiscale modelling of the structural integrity of composite materials'.
Ian Sinclair - One of the best experts on this subject based on the ideXlab platform.
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Benchmarking of strength models for unidirectional composites under longitudinal tension
Composites Part A: Applied Science and Manufacturing, 2018Co-Authors: Anthony Bunsell, Ian Sinclair, Yentl Swolfs, Larissa Gorbatikh, Hannah Morton, Soraia Pimenta, Mark Spearing, Alain ThionnetAbstract:Several modelling approaches are available in the literature to predict longitudinal tensile failure of Fibre-reinforced polymers. However, a systematic, blind and unbiased comparison between the predictions from the different models and against experimental data has never been performed. This paper presents a benchmarking exercise performed for three different models from the literature: (i) an analytical hierarchical scaling law for composite Fibre bundles, (ii) direct numerical simulations of composite Fibre bundles, and (iii) a multiscale finite-element simulation method. The results show that there are significant discrepancies between the predictions of the different modelling approaches for Fibre-Break density evolution, cluster formation and ultimate strength, and that each of the three models presents unique advantages over the others. Blind model predictions are also compared against detailed computed-tomography experiments, showing that our understanding of the micromechanics of longitudinal tensile failure of composites needs to be developed further.
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Synchrotron radiation computed tomography for experimental validation of a tensile strength model for unidirectional Fibre-reinforced composites
Composites Part A: Applied Science and Manufacturing, 2015Co-Authors: Yentl Swolfs, A.e. Scott, S.m. Spearing, Ian Sinclair, Larissa Gorbatikh, H. Morton, Philippa Reed, Ignace VerpoestAbstract:Synchrotron radiation computed tomography has been used to analyse Fibre Break accumulation in unidirectional composites loaded in tension. The data are compared to model predictions. The model only slightly overestimated the composite failure strain, but predictions of Fibre Break density were too high, which can be mainly attributed to errors in the Weibull distribution. Both the number and percentage of interacting Fibre Break clusters were under-predicted by the model. This was attributed to an underestimation of stress concentrations in the model. While the experimental observations revealed mainly co-planar clusters, the model predicted mainly diffuse clusters. The experiments showed that the clusters did grow any further after their formation, while the model predicted a gradual development. Both local and dynamic stress concentrations were hypothesised to be key features for further exploration. The discrepancies identified, inform suggestions for directions advancing the state-of-the-art strength models of UD composites.
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Influence of voids on damage mechanisms in carbon/epoxy composites determined via high resolution computed tomography
Composites Science and Technology, 2014Co-Authors: A.e. Scott, Mark Mavrogordato, S.m. Spearing, Ian Sinclair, Warren HepplesAbstract:A multi-scale computed tomography (CT) technique has been used to determine the material structure and damage mechanisms in hydrostatically loaded composite circumferential structures. Acoustic emission sensing was used to locate macroscopically regions of high damage under load to inform the computed tomography. The resultant images allow direct three-dimensional analysis of voids, Fibre Breaks and cracking, for which a high level of confidence can be placed in the results when compared to other indirect and/or surface-based methods. Ex situ analysis of loaded samples revealed matrix cracking in the longitudinally wound plies, whilst Fibre Breaks were observed in the circumferentially wound plies. The matrix cracking within the longitudinally wound plies is shown to interact directly with intralaminar voids. The correlation of voids with Fibre Breaks in the circumferentially wound plies is less distinct. A three-dimensional tessellation technique was used to analyse the spatial distribution of the voids and to compare with single Fibre Break locations. Whilst there was no first order correlation between Fibre Break densities and void volume fractions or void dimensions, a distinct correlation was found between voids and nearest neighbouring Fibre Breaks, where 2.6-5 times more Fibre Breaks occurred immediately adjacent to a void than would be expected for randomly distributed Breaks. (C) 2013 Elsevier Ltd. All rights reserved.
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High resolution damage detection of loaded carbon/epoxy laminates using synchrotron radiation computed tomography
2011Co-Authors: A.e. Scott, Mark Mavrogordato, Warren Hepples, Ian Sinclair, Peter Wright, N. Kalantzis, S.m. SpearingAbstract:The inherent anisotropy and heterogeneity of polymer matrix composites leads to complex macro and micro-mechanical material behaviour. Many micro-mechanical theories exist to predict the failure of unidirectional composites, for example the strength distribution and stress transfer models of Rosen, Batdorf and Hedgepeth. However experimental analysis to confirm the underpinning assumptions made in these theories is limited and hence the validity of the work has not yet been fully determined. Conventional micromechnical assessment methods however are limited, typically having one or more of the following constraints; destructive, time consuming, low spatial resolution or mechanistic ambiguity. Contemporary computed tomography (CT) methods have great potential to overcome these problems, providing resolutions (to sub-micron levels) at sample scales that may allow multiple damage mechanisms to be quantified in three dimensions. In the present work, high-resolution synchrotron radiation computed tomography (SRCT) results have been obtained for a commercial grade carbon/epoxy composite laminate under load that is widely used in engineering applications. The double edge notched [90/0]s laminate plates were loaded in-situ to failure and scanned in the preloaded state, and then at incrementally increasing stress levels to the point of final failure. The imaging techniques enable major damage mechanisms to be identified and quantified, with the present work particularly focused on individual Fibres Breaks. To the authors' knowledge it provides the first detailed quantification of the accumulation of broken Fibres in a carbon/epoxy laminate up to a near-failure condition. It can be seen that failure of Fibres is the dominant damage mechanism controlling tensile fracture stress. The incidence of Fibre Break clusters evidences the role of load sharing in the build up of a failure. No correlation was found between the location of matrix cracks in the 90° plies and Fibre Breaks in the 0°ply. At present the image analysis has shown no obvious correlation between the location of Fibre Breaks and other micro-structural features, i.e. presence of voids and resin rich regions. However the data obtained in this experiment gives scope for further quantification.
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In situ Fibre fracture measurement in carbon-epoxy laminates using high resolution computed tomography
Composites Science and Technology, 2011Co-Authors: A.e. Scott, Mark Mavrogordato, Ian Sinclair, Peter Wright, S.m. SpearingAbstract:High resolution Synchrotron Radiation Computed Tomography (SRCT) has been used to capture Fibre damage progression in a carbon–epoxy notched [90/0]s laminate loaded to failure. To the authors knowledge this provides the first direct in situ measurement of the accumulation of Fibre fractures for a high performance material under structurally relevant load conditions (i.e. fractures within the bulk of an essentially conventional engineering laminate). A high level of confidence is placed in the measurements, as the failure processes are viewed internally at the relevant micromechanical length-scales, as opposed to previous indirect and/or surface-based methods. Whilst Fibre Breaks are the dominant composite damage mechanism considered in the present work, matrix damage, such as transverse ply cracks, 0? splits and delaminations, were also seen to occur in advance of extensive Fibre Breaks. At loads where Fibre Break density levels were significant, splitting and delamination were seen to separate the central 0? ply in the near notch region from the 90? plies. Fibre Breaks were initially observed in isolated locations, consistent with the stochastic nature of Fibre strengths. The formation of clusters of broken Fibres was observed at higher loads. The largest clusters observed consisted of a group of eleven Breaks and a group of fourteen Breaks. The large clusters were observed at the highest load, at sites with no prior Breaks, indicating they occurred within a relatively narrow load range. No strong correlation was found between the location of matrix damage and Fibre Breaks. The data achieved has been made available online at www.materialsdatacentre.com for ongoing model development and validation.
Frank R. Jones - One of the best experts on this subject based on the ideXlab platform.
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Six image phase stepped photoelasticity for the quantification of the stress field around 25 μm reinforcing Fibres
Composites Science and Technology, 2010Co-Authors: Zheng Liu, F.m. Zhao, Frank R. JonesAbstract:A six image phase stepped photoelastic technique has been applied for the measurement of the interfacial shear stress distribution in the matrix resin along a reinforcing E-glass Fibre of ∼25 μm in diameter at its end and at a Fibre-Break. Contour maps of the isochromatic fringe order and its corresponding isoclinic angle, which are related to the principal stress difference and direction relative to the Fibre axis, could be obtained continuously using this photoelastic technique. Thus the actual interfacial shear stress along the Fibre can be calculated. Furthermore in the presence of a Fibre-Break, interfacial debonding and matrix yielding during stress transfer was investigated. The micro-mechanics are shown to differ at a Fibre-Break compared to a Fibre-end.
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Improving the prediction of tensile failure in unidirectional Fibre composites by introducing matrix shear yielding
Composites Science and Technology, 2009Co-Authors: Shabnam Behzadi, Paul T. Curtis, Frank R. JonesAbstract:A Monte Carlo simulation is established to predict the failure strain of unidirectional Fibre composites. The effect of matrix shear yielding of a high performance epoxy resin is introduced into the model through load sharing factors between the Fibres adjacent to Fibre-Break(s). Strain concentration factors (SCF) of Fibres are obtained using Finite Element Methods (FEM) in a three dimensional multi-Fibre unit cell containing one, two and three adjoining Fibre-Break(s). The tensile strains of the surviving adjacent Fibres are intensified as a function of their distances from the fracture. A statistical simulation is carried out to predict the failure strain of a single layer of unidirectional (UD) Fibre composites with the thickness of the Fibre ineffective length. Using the weakest link theory, the ultimate failure strain of a real size UD composite is predicted.
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Hierarchical modelling of a polymer matrix composite
Journal of Materials Science, 2008Co-Authors: Joel P. Foreman, Shabnam Behzadi, Paul T. Curtis, David Porter, Frank R. JonesAbstract:A hierarchical modelling scheme to predict the properties of a polymer matrix composite is introduced. The stress–strain curves of amine-cured tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) cured have been predicted using group interaction modelling (GIM). The GIM method, originally applied primarily to linear polymers, has been significantly extended to give accurate, consistent results for TGDDM, a highly crosslinked two-component matrix. The model predicts a complete range of temperature-dependent properties, from fundamental energy contributions, through engineering moduli to full stress–strain curves through yield. The predicted properties compare very well with experiment. Using the GIM-predicted TGDDM stress–strain curve, a 3D finite element model is used to obtain strain concentration factors (SCF) of Fibres adjacent to a Fibre Break in a unidirectional (UD) composite. The strain distribution among the intact neighbouring Fibres is clearly affected by the yielding mechanism in the resin matrix. A Monte Carlo simulation is carried out to predict the tensile failure strain of a single composite layer with the thickness equal to the Fibre ineffective length. The effect of matrix shear yielding is introduced to the model through the SCF of surviving Fibres adjacent to the Fibre-Break. The tensile failure strain of the composite is then predicted using a statistical model of a chain of composite layers.
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Photoelastic Determination of Interfacial Shear Stresses in Model Composites
Key Engineering Materials, 2007Co-Authors: F.m. Zhao, Frank R. JonesAbstract:Phase-stepping photoelasticity has been used to study the fragmentation of an E-glass Fibre in epoxy resin and examine quantitatively the effect of a transverse matrix crack on the stress transfer at an interphase. Unsized glass Fibre was coated by plasma polymerisation with a crosslinked conformal film of 90% acrylic acid and 10% 1,7-octadiene. The micro-mechanical response at the Fibre-matrix interphase and in the adjacent matrix has been described in detail using contour maps of fringe order. From these, the interfacial shear stress profiles at Fibre-Break have been calculated.
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Photoelastic study of the stress transfer in single Fibre composites
Composite Interfaces, 2006Co-Authors: F.m. Zhao, Simon A. Hayes, R. J. Young, Frank R. JonesAbstract:The stress transfer between a single Fibre and a matrix has been studied using the technique of automated phase-stepping photoelasticity. The contours of isochromatic fringe order provide the locations and magnitude of maximum shear stress. A model composite in which a Fibre-Break leads to the propagation of a matrix crack has been used to compare the interfacial shear stresses around bonded and debonded interfaces in the absence and presence of a Fibre-Break and matrix cracks.
S.m. Spearing - One of the best experts on this subject based on the ideXlab platform.
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Synchrotron radiation computed tomography for experimental validation of a tensile strength model for unidirectional Fibre-reinforced composites
Composites Part A: Applied Science and Manufacturing, 2015Co-Authors: Yentl Swolfs, A.e. Scott, S.m. Spearing, Ian Sinclair, Larissa Gorbatikh, H. Morton, Philippa Reed, Ignace VerpoestAbstract:Synchrotron radiation computed tomography has been used to analyse Fibre Break accumulation in unidirectional composites loaded in tension. The data are compared to model predictions. The model only slightly overestimated the composite failure strain, but predictions of Fibre Break density were too high, which can be mainly attributed to errors in the Weibull distribution. Both the number and percentage of interacting Fibre Break clusters were under-predicted by the model. This was attributed to an underestimation of stress concentrations in the model. While the experimental observations revealed mainly co-planar clusters, the model predicted mainly diffuse clusters. The experiments showed that the clusters did grow any further after their formation, while the model predicted a gradual development. Both local and dynamic stress concentrations were hypothesised to be key features for further exploration. The discrepancies identified, inform suggestions for directions advancing the state-of-the-art strength models of UD composites.
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Influence of voids on damage mechanisms in carbon/epoxy composites determined via high resolution computed tomography
Composites Science and Technology, 2014Co-Authors: A.e. Scott, Mark Mavrogordato, S.m. Spearing, Ian Sinclair, Warren HepplesAbstract:A multi-scale computed tomography (CT) technique has been used to determine the material structure and damage mechanisms in hydrostatically loaded composite circumferential structures. Acoustic emission sensing was used to locate macroscopically regions of high damage under load to inform the computed tomography. The resultant images allow direct three-dimensional analysis of voids, Fibre Breaks and cracking, for which a high level of confidence can be placed in the results when compared to other indirect and/or surface-based methods. Ex situ analysis of loaded samples revealed matrix cracking in the longitudinally wound plies, whilst Fibre Breaks were observed in the circumferentially wound plies. The matrix cracking within the longitudinally wound plies is shown to interact directly with intralaminar voids. The correlation of voids with Fibre Breaks in the circumferentially wound plies is less distinct. A three-dimensional tessellation technique was used to analyse the spatial distribution of the voids and to compare with single Fibre Break locations. Whilst there was no first order correlation between Fibre Break densities and void volume fractions or void dimensions, a distinct correlation was found between voids and nearest neighbouring Fibre Breaks, where 2.6-5 times more Fibre Breaks occurred immediately adjacent to a void than would be expected for randomly distributed Breaks. (C) 2013 Elsevier Ltd. All rights reserved.
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High resolution damage detection of loaded carbon/epoxy laminates using synchrotron radiation computed tomography
2011Co-Authors: A.e. Scott, Mark Mavrogordato, Warren Hepples, Ian Sinclair, Peter Wright, N. Kalantzis, S.m. SpearingAbstract:The inherent anisotropy and heterogeneity of polymer matrix composites leads to complex macro and micro-mechanical material behaviour. Many micro-mechanical theories exist to predict the failure of unidirectional composites, for example the strength distribution and stress transfer models of Rosen, Batdorf and Hedgepeth. However experimental analysis to confirm the underpinning assumptions made in these theories is limited and hence the validity of the work has not yet been fully determined. Conventional micromechnical assessment methods however are limited, typically having one or more of the following constraints; destructive, time consuming, low spatial resolution or mechanistic ambiguity. Contemporary computed tomography (CT) methods have great potential to overcome these problems, providing resolutions (to sub-micron levels) at sample scales that may allow multiple damage mechanisms to be quantified in three dimensions. In the present work, high-resolution synchrotron radiation computed tomography (SRCT) results have been obtained for a commercial grade carbon/epoxy composite laminate under load that is widely used in engineering applications. The double edge notched [90/0]s laminate plates were loaded in-situ to failure and scanned in the preloaded state, and then at incrementally increasing stress levels to the point of final failure. The imaging techniques enable major damage mechanisms to be identified and quantified, with the present work particularly focused on individual Fibres Breaks. To the authors' knowledge it provides the first detailed quantification of the accumulation of broken Fibres in a carbon/epoxy laminate up to a near-failure condition. It can be seen that failure of Fibres is the dominant damage mechanism controlling tensile fracture stress. The incidence of Fibre Break clusters evidences the role of load sharing in the build up of a failure. No correlation was found between the location of matrix cracks in the 90° plies and Fibre Breaks in the 0°ply. At present the image analysis has shown no obvious correlation between the location of Fibre Breaks and other micro-structural features, i.e. presence of voids and resin rich regions. However the data obtained in this experiment gives scope for further quantification.
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In situ Fibre fracture measurement in carbon-epoxy laminates using high resolution computed tomography
Composites Science and Technology, 2011Co-Authors: A.e. Scott, Mark Mavrogordato, Ian Sinclair, Peter Wright, S.m. SpearingAbstract:High resolution Synchrotron Radiation Computed Tomography (SRCT) has been used to capture Fibre damage progression in a carbon–epoxy notched [90/0]s laminate loaded to failure. To the authors knowledge this provides the first direct in situ measurement of the accumulation of Fibre fractures for a high performance material under structurally relevant load conditions (i.e. fractures within the bulk of an essentially conventional engineering laminate). A high level of confidence is placed in the measurements, as the failure processes are viewed internally at the relevant micromechanical length-scales, as opposed to previous indirect and/or surface-based methods. Whilst Fibre Breaks are the dominant composite damage mechanism considered in the present work, matrix damage, such as transverse ply cracks, 0? splits and delaminations, were also seen to occur in advance of extensive Fibre Breaks. At loads where Fibre Break density levels were significant, splitting and delamination were seen to separate the central 0? ply in the near notch region from the 90? plies. Fibre Breaks were initially observed in isolated locations, consistent with the stochastic nature of Fibre strengths. The formation of clusters of broken Fibres was observed at higher loads. The largest clusters observed consisted of a group of eleven Breaks and a group of fourteen Breaks. The large clusters were observed at the highest load, at sites with no prior Breaks, indicating they occurred within a relatively narrow load range. No strong correlation was found between the location of matrix damage and Fibre Breaks. The data achieved has been made available online at www.materialsdatacentre.com for ongoing model development and validation.
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Comparison of the accumulation of Fibre Breaks occurring in a unidirectional carbon/epoxy composite identified in a multi-scale micro-mechanical model with that of experimental observations using high resolution computed tomography
2010Co-Authors: A.e. Scott, Anthony Bunsell, Mark Mavrogordato, S.m. Spearing, I. Sinclair, Alain ThionnetAbstract:A model to predict Fibre Break accumulation that takes into account all physical phenomena at the origin of the Fibre Break (i.e. the random nature, stress transfer due to Breaks, Fibre debonding and viscosity of the matrix) shows clearly that the failure of a unidirectional composite structure results in the formation of random Fibre Breaks which at higher loads coalesce into clusters of broken Fibres. The object of the study is to experimentally confirm this scenario. Many techniques exist to detect the failure of carbon Fibre composites, however none of them offer a resolution that allows this goal to be achieved in a non-destructive manner and in three dimensions. High resolution computed tomography has been used to confirm the scenario modelled. A sample was tested and observed in-situ at the European Synchrotron Research Facilities, ESRF, Grenoble. All Fibre Breaks arising in the vicinity of the final rupture of a unidirectional composite have been detected and the formation of clusters can be observed.