The Experts below are selected from a list of 81 Experts worldwide ranked by ideXlab platform
Chandra Veer Singh - One of the best experts on this subject based on the ideXlab platform.
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assessing progressive failure in long wind turbine blades under quasi static and cyclic loads
Renewable Energy, 2018Co-Authors: John Montesano, Yangjie Zuo, Chandra Veer SinghAbstract:Predicting progressive failure and consequential loss in the load-bearing capability of large-scale composite wind blades is vital for accurately assessing their service life and maintenance. A physics-based multi-scale damage model describing progressive Ply Cracking and joint adhesive debonding in blades under both quasi-static and cyclic loading is presented. The complete structure of the blade was considered including the shell-spar adhesive joint and shell-root adhesive joint. For quasi-static loading, the geometrical transition region of the blade was observed as the critical Ply Crack damage region, which was in agreement with previous experimental results. The matrix micro-Cracking damage was mainly caused by high gale wind speeds, and adhesive debonding ultimately initiated at the shell-spar joint. The blade tip deflection increased nonlinearly with increasing wind speeds, reaching 29.0% of the blade length at 19 m/s. For cyclic loading, sub-critical damage grew along the length of the blade with increasing cycles, gradually increasing the normal and shear stresses in the joint adhesive layer as the Crack density increased, eventually leading to local shell-spar adhesive debonding. The simulation methodology presented here will be useful for assessing the durability and increasing the safety and accuracy of service life prediction of large-scale blade structures.
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prediction of Ply Crack evolution and stiffness degradation in multidirectional symmetric laminates under multiaxial stress states
Composites Part B-engineering, 2018Co-Authors: John Montesano, Brent Mccleave, Chandra Veer SinghAbstract:Abstract A comprehensive study was performed to assess the influence of microscopic Ply Crack interactions on Crack surface opening (COD) and sliding displacements (CSD) for arbitrary plies in general symmetric multidirectional laminates under multiaxial stresses. Based on a generated database, general unified expressions for determining both CODs and CSDs at various Crack densities were developed and used with a multiscale damage-based model to predict stiffness degradation and Ply Crack evolution for cross-Ply, angle-Ply and quasi-isotropic laminates. The predicted elastic properties for laminates containing Cracks in individual plies, as well as simultaneous Cracks in multiple plies, were found to correlate well with data from independent finite element analysis, while Crack density predictions were validated with available experimental data. The developed unified expressions have increased the robustness and range of applicability of our damage-based multiscale model. Meanwhile, the ability of the model to predict simultaneous Cracking in multiple plies and both intra-Ply and inter-Ply Crack interactions for laminates under combines stresses is regarded as advantageous. The model can be invoked to efficiently predict Ply Crack evolution in laminates, and when combined with a suitable delamination model may be used as a design tool to assess the long-term durability of critical load-bearing structures.
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predicting evolution of Ply Cracks in composite laminates subjected to biaxial loading
Composites Part B-engineering, 2015Co-Authors: John Montesano, Chandra Veer SinghAbstract:An energy-based model is developed to predict the evolution of sub-critical matrix Crack density in symmetric multidirectional composite laminates for the case of multiaxial loading. A finite elementbased numerical scheme is also developed to evaluate the critical strain energy release rate, GIc, associated with matrix micro-Cracking, a parameter that previously required fitting with experimental data. Furthermore, the prediction scheme is improved to account for the statistical variation of GIc within the material volume by using a two-parameter Weibull distribution. The variation of GIc with increasing Crack density is also accounted for based on reported experimental evidence. The simulated results for carbon/epoxy and glass/epoxy cross-Ply laminates demonstrate the ability of the improved model to predict the evolution of multidirectional Ply Cracking. By integrating this damage evolution model with the synergistic damage mechanics approach for stiffness degradation, the stress-strain response of the studied laminates is predicted. Finally, biaxial stress envelopes for Ply Crack initiation and predetermined stiffness degradation levels are predicted to serve as representative examples of stiffnessbased design and failure criterion.
John Montesano - One of the best experts on this subject based on the ideXlab platform.
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assessing the effects of Ply constraints on local stress states in cross Ply laminates containing manufacturing induced defects
Composites Part B-engineering, 2020Co-Authors: Farzad Sharifpour, John Montesano, Ramesh TalrejaAbstract:Abstract Computational micromechanics is employed to assess the influence of Ply constraints on the early stages of 90° Ply Crack formation in a cross-Ply laminate under tensile loading. Manufacturing induced defects, including nonuniform fiber spatial distribution, microvoids and microCracks, are explicitly simulated. Local distortion and dilatation energy density values in the matrix, associated with local yielding and brittle cavitation, are assessed within unconstrained and constrained 90° plies. The effects of Ply constraints are found to emerge when pre-existing microvoids or microCracks are present, while dissimilar levels of constraining are observed in distinct regions of the Ply, e.g. fiber clusters versus resin-rich zones. These important results reveal that for constrained plies variations in the local deformation fields within these regions and their interdependency directly influence Crack nucleation and its subsequent evolution. Additional parametric studies show the influence of pre-existing microvoid and microCrack sizes on the degree of Ply constraining. Furthermore, the effect of the constrained and adjacent Ply thicknesses, Ply interface resin-rich layer thickness, and post-cure thermal cooldown on the degree of constraining are also considered. The study provides an improved understanding of the early stages of Ply Crack formation in constrained plies, which is important for predicting damage evolution in laminates and for using the lowest damage thresholds for safe designs.
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influence of in situ constraining effect on transverse Ply Crack formation in unidirectional composite laminates
Proceedings of the American Society for Composites — Thirty-fourth Technical Conference, 2019Co-Authors: Farzad Sharifpour, John MontesanoAbstract:A micromechanical finite element model was developed to predict the initial events of failure in the constrained 90° Ply of a [0/90/0] unidirectional cross-Ply laminate under in-plane tensile loading. Common manufacturing induced defects, including non-uniform fiber spatial distribution and voids, were considered in the explicit representation of the full thickness multi-fiber 90° Ply, while the constraining 0° plies were treated as effectively homogeneous orthotropic materials. The inelastic behavior of the polymeric matrix in the 90° Ply was modeled via a pressure-dependent yield criterion, while the carbon fibers were assumed to deform linear elastically. Two metrics for representing failure were considered in the assessment, including distortional and dilatational energy densities that are respectively responsible for local yielding and cavitation in the fiberconstrained matrix. The influence of in-situ effect was studied by comparing the local stress state of the constrained and unconstrained transverse Ply. It was observed that the local response of the polymer depends on the fiber spatial distribution. Furthermore, it was found that the in-situ Ply constraining effect appears subsequent to the formation of local Cracks and not prior. Dissimilar constraining effects were observed in different regions, e.g., resin-rich zone versus fiber-cluster zone, suggesting that inconsistent stress distributions will directly influence the evolution of Cracks in the 90° Ply.
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assessing progressive failure in long wind turbine blades under quasi static and cyclic loads
Renewable Energy, 2018Co-Authors: John Montesano, Yangjie Zuo, Chandra Veer SinghAbstract:Predicting progressive failure and consequential loss in the load-bearing capability of large-scale composite wind blades is vital for accurately assessing their service life and maintenance. A physics-based multi-scale damage model describing progressive Ply Cracking and joint adhesive debonding in blades under both quasi-static and cyclic loading is presented. The complete structure of the blade was considered including the shell-spar adhesive joint and shell-root adhesive joint. For quasi-static loading, the geometrical transition region of the blade was observed as the critical Ply Crack damage region, which was in agreement with previous experimental results. The matrix micro-Cracking damage was mainly caused by high gale wind speeds, and adhesive debonding ultimately initiated at the shell-spar joint. The blade tip deflection increased nonlinearly with increasing wind speeds, reaching 29.0% of the blade length at 19 m/s. For cyclic loading, sub-critical damage grew along the length of the blade with increasing cycles, gradually increasing the normal and shear stresses in the joint adhesive layer as the Crack density increased, eventually leading to local shell-spar adhesive debonding. The simulation methodology presented here will be useful for assessing the durability and increasing the safety and accuracy of service life prediction of large-scale blade structures.
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prediction of Ply Crack evolution and stiffness degradation in multidirectional symmetric laminates under multiaxial stress states
Composites Part B-engineering, 2018Co-Authors: John Montesano, Brent Mccleave, Chandra Veer SinghAbstract:Abstract A comprehensive study was performed to assess the influence of microscopic Ply Crack interactions on Crack surface opening (COD) and sliding displacements (CSD) for arbitrary plies in general symmetric multidirectional laminates under multiaxial stresses. Based on a generated database, general unified expressions for determining both CODs and CSDs at various Crack densities were developed and used with a multiscale damage-based model to predict stiffness degradation and Ply Crack evolution for cross-Ply, angle-Ply and quasi-isotropic laminates. The predicted elastic properties for laminates containing Cracks in individual plies, as well as simultaneous Cracks in multiple plies, were found to correlate well with data from independent finite element analysis, while Crack density predictions were validated with available experimental data. The developed unified expressions have increased the robustness and range of applicability of our damage-based multiscale model. Meanwhile, the ability of the model to predict simultaneous Cracking in multiple plies and both intra-Ply and inter-Ply Crack interactions for laminates under combines stresses is regarded as advantageous. The model can be invoked to efficiently predict Ply Crack evolution in laminates, and when combined with a suitable delamination model may be used as a design tool to assess the long-term durability of critical load-bearing structures.
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predicting evolution of Ply Cracks in composite laminates subjected to biaxial loading
Composites Part B-engineering, 2015Co-Authors: John Montesano, Chandra Veer SinghAbstract:An energy-based model is developed to predict the evolution of sub-critical matrix Crack density in symmetric multidirectional composite laminates for the case of multiaxial loading. A finite elementbased numerical scheme is also developed to evaluate the critical strain energy release rate, GIc, associated with matrix micro-Cracking, a parameter that previously required fitting with experimental data. Furthermore, the prediction scheme is improved to account for the statistical variation of GIc within the material volume by using a two-parameter Weibull distribution. The variation of GIc with increasing Crack density is also accounted for based on reported experimental evidence. The simulated results for carbon/epoxy and glass/epoxy cross-Ply laminates demonstrate the ability of the improved model to predict the evolution of multidirectional Ply Cracking. By integrating this damage evolution model with the synergistic damage mechanics approach for stiffness degradation, the stress-strain response of the studied laminates is predicted. Finally, biaxial stress envelopes for Ply Crack initiation and predetermined stiffness degradation levels are predicted to serve as representative examples of stiffnessbased design and failure criterion.
L.n. Mccartney - One of the best experts on this subject based on the ideXlab platform.
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approximate method of predicting Ply Crack formation in general symmetric laminates subject to biaxial loading and bending
2008Co-Authors: L.n. MccartneyAbstract:Ply Cracking is a very important damage mode for laminated composite materials that has been the subject of intensive study over many years, especially cross-Ply laminates. In practical applications, laminates are usually more complex than cross-plies, and they are subject to complex loading that involves both in-plane and out-of-plane deformation, in addition to residual stresses arising from thermal expansion mismatch effects between the plies. Based on a methodology that is able to predict Ply Cracking for: i) a multiple-Ply cross-Ply laminate subject to combined biaxial in-plane loading and biaxial bending, and ii) a general symmetric laminate subject to combined in-plane biaxial loading and in-plane shear loading, where thermal residual stresses can be present, this paper will attempt to combine the models developed for these situations so that Ply Cracking in general symmetric laminates subject to combined in-plane biaxial and out-of-plane biaxial bending can be treated. It is first assumed that laminates have at least one 90o Ply, and that Ply Cracking occurs only in some of all of the 90o plies. The off-axis plies in the laminate, which are unCracked, are first homogenised into an orthotropic effective medium. The next step is to apPly the homogenised properties to the 0o plies of an equivalent hybrid cross-Ply laminate that is then subject to progressive loading involving any combination of in-plane biaxial loading and out-of-plane bending. The homogenisation approach is tested, for the case of uniaxial in-plane loading, by comparing predictions of the homogenised model with those of an existing model that allows for the presence of all the off-axis plies. For more complex loading states, an example will be given of a prediction of the progressive growth of Ply Cracking, and of laminate stress-strain behaviour.
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Energy-based prediction of progressive Ply Cracking and strength of general symmetric laminates using an homogenisation method
Composites Part A: Applied Science and Manufacturing, 2005Co-Authors: L.n. MccartneyAbstract:This article describes the application to a range of laminates of a recently developed homogenisation technique for general symmetric laminates that enables progressive Ply Cracking to be predicted in a laminate containing any number of plies having a variety of orientations. The energy-based methodology may be applied in conjunction with a strain-based fibre failure criterion to predict progressive Ply Crack formation and the strength of the laminate for situations where the laminate is subject to general in-plane loading and thermal residual stresses. The comparison of model performance with some experimental results for uniaxial loading described in the literature, for a range of laminate geometries without 0° plies, indicates that the model correctly takes account of the effects of varying Ply thicknesses. The predicted maximum stress applied during a Ply Cracking simulation can be a very good estimate of the laminate strength when Ply Cracking is the principal mode of damage, i.e. delamination is minimal. The comparison of model performance with experimental results in the literature, for quasi-isotropic laminates with 0° plies having four different lay-ups, shows there is good agreement. The model indicates that there is a Ply lay-up effect, and that fibre fracture occurs at the point of laminate failure. It is shown that by placing 90° plies adjacent to the mid-plane of the laminate, the strength of the laminate is slightly reduced.
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effect of mixed mode loading on Ply Crack development in laminated composites theory and application
2004Co-Authors: L.n. MccartneyAbstract:Mixed mode loading is always encountered near stress concentrations in composite components, such as holes in general symmetric laminates. The stress concentration effects lead to stress states that are a combination of biaxial and shear loading modes so that a mixed mode situation must be taken into account when considering the formation of Ply Cracking near the stress concentrations. This report is concerned with a proposed methodology for the development of a technique that can account for the effects of mixed mode loading on Ply Crack development in general symmetric laminates. The approach will indicate how the methodology, already developed to predict the effects of Ply Cracking on laminate properties when Ply Crack growth occurs in mode I loading, can be extended to deal with Ply Crack growth in the mixed mode situations. These arise in practical applications, where combined mode I and mode II deformations are encountered at Ply Crack tips. The problem splits into two distinct stages. The first concerns the estimation of the availability of energy for Ply Crack development under mixed mode conditions that is addressed in this report. The second involves understanding the factors that control the resistance of the material in mixed mode situations (i.e. its effective fracture toughness). The criterion for first Ply failure is based on a general form of energy balance that is designed to be flexible. It is clear from the preliminary results presented in this report that the choice of Ply Cracking criterion has a significant effect on the predictions for first Ply failure. In particular it has been shown that the use of a total energy release rate criterion, in situations where Ply Crack growth is mixed mode, leads to predictions that are physically unreasonable, thus indicating the importance of deriving a physically realistic criterion for Ply Cracking. The analysis presented in this report is to be the basis of modifications to a software system that has recently been developed using homogenisation techniques to take account of Ply Crack formation in more than one orientation in any general symmetric laminate. The inclusion of mixed mode effects are expected to lead to more accurate simulations of both damage development and strength predictions. The software will also be used to upgrade the PREDICT module of the NPL Composites Design Analysis (CoDA) software system.
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chapter 5 5 prediction of Ply Crack formation and failure in laminates
Failure Criteria in Fibre-Reinforced-Polymer Composites#R##N#The World-Wide Failure Exercise, 2004Co-Authors: L.n. MccartneyAbstract:Publisher Summary This chapter presents, for a [0/90]s cross-Ply laminate subject to uniaxial loading, the results of comparisons between the model predictions of stress/strain behavior carried out in Part A of the Failure Exercise and the corresponding experimental data provided after the predictions had been made. Because a new model designed for general symmetric laminates has since been developed, comparisons are shown between the stress/strain predictions of the new model applied to quasi-isotropic and [ ±θ]s laminates (with θ = 45 and 55°) and the corresponding experimental data provided to participants in the failure exercise. Very good correlations between the model and experimental stress/strain data have been achieved for both the cross-Ply and quasi-isotropic laminates (subject to both uniaxial and biaxial loading), principally because Ply Cracking in a single orientation is expected to occur for a significant part of the stress/strain curves. Additional damage modes must be taken into account (fiber fracture) before predictions of strength can be made that are based on the modeling of physical micro-mechanisms associated with laminate failure. A rudimentary physically based approach to the prediction of laminate failure is made by considering fiber strain within the laminate in relation to the average failure strain of a single fiber. The chapter presents the assessment of the Ply Cracking models, which lead to good predictions of laminate stress/strain behavior that is consistent with data provided for the Failure Exercise.
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prediction of Ply Crack formation and failure in laminates
Composites Science and Technology, 2002Co-Authors: L.n. MccartneyAbstract:Abstract For a [0/90] s cross-Ply laminate subject to uniaxial loading, this paper presents the results of comparisons between the model predictions of stress/strain behaviour, carried out in Part A of the Failure Exercise, and the corresponding experimental data provided after the predictions had been made. In addition, because a new model designed for general symmetric laminates has since been developed, comparisons are shown between the stress/strain predictions of the new model applied to quasi-isotropic and [± θ ] s laminates (with θ=45 and 55°), and the corresponding experimental data provided to participants in the failure exercise. Very good correlations between the model and experimental stress/strain data have been achieved for both the cross-Ply and quasi-isotropic laminates (subject to both uniaxial and biaxial loading), principally because Ply Cracking in a single orientation is expected to occur for a significant part of the stress/strain curves. The correlation for [± θ ] s laminates is not as good because the model is not able to account for Ply Crack formation in both the + θ and − θ plies of the laminate. In addition, the model has not yet been modified to deal with mixed-mode Ply Crack growth, or with non-linear matrix behaviour which could lead to significant deviations between model predictions and experimental results at large strains. It is emphasised that the models used are not able by themselves to predict strength. Additional damage modes must be taken into account (e.g. fibre fracture) before predictions of strength can be made that are based on the modelling of physical micro-mechanisms associated with laminate failure. A rudimentary physically based approach to the prediction of laminate failure is made by considering fibre strain within the laminate in relation to the average failure strain of a single fibre. The Ply Cracking models that have been assessed in the paper, for cases where they are expected to be valid, have been shown to lead to good predictions of laminate stress/strain behaviour that is consistent with data provided for the Failure Exercise. The reliability of the models is such that they have good potential for being used as the basis of new design methodology to deal with initial Ply Crack formation in laminates, and the effects of Ply Cracking on non-linear stress/strain behaviour for parts of stress/strain curves where Ply Cracking occurs in a single orientation.
Ramesh Talreja - One of the best experts on this subject based on the ideXlab platform.
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assessing the effects of Ply constraints on local stress states in cross Ply laminates containing manufacturing induced defects
Composites Part B-engineering, 2020Co-Authors: Farzad Sharifpour, John Montesano, Ramesh TalrejaAbstract:Abstract Computational micromechanics is employed to assess the influence of Ply constraints on the early stages of 90° Ply Crack formation in a cross-Ply laminate under tensile loading. Manufacturing induced defects, including nonuniform fiber spatial distribution, microvoids and microCracks, are explicitly simulated. Local distortion and dilatation energy density values in the matrix, associated with local yielding and brittle cavitation, are assessed within unconstrained and constrained 90° plies. The effects of Ply constraints are found to emerge when pre-existing microvoids or microCracks are present, while dissimilar levels of constraining are observed in distinct regions of the Ply, e.g. fiber clusters versus resin-rich zones. These important results reveal that for constrained plies variations in the local deformation fields within these regions and their interdependency directly influence Crack nucleation and its subsequent evolution. Additional parametric studies show the influence of pre-existing microvoid and microCrack sizes on the degree of Ply constraining. Furthermore, the effect of the constrained and adjacent Ply thicknesses, Ply interface resin-rich layer thickness, and post-cure thermal cooldown on the degree of constraining are also considered. The study provides an improved understanding of the early stages of Ply Crack formation in constrained plies, which is important for predicting damage evolution in laminates and for using the lowest damage thresholds for safe designs.
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fatigue damage and fatigue life diagrams of a carbon epoxy cross Ply laminate aged by hygrothermal exposure
Composites Part A-applied Science and Manufacturing, 2019Co-Authors: Ana Paula Pereira Fulco, Ramesh Talreja, Antonio Marcos De Medeiros, Maikson L P Tonatto, Sandro Campos Amico, Jose Daniel D MeloAbstract:Abstract This study concerns the effects of hygrothermal aging on failure of carbon/epoxy composites subjected to fatigue loading. AS4/8552 laminates with stacking sequence [02/902]s are exposed to cycles of 4 h at 160 °C followed by 8 h of 80% average relative humidity at 70 °C, for a total exposure time of 2880 h. Fourier transform infrared (FTIR) spectroscopy, dynamic mechanical analysis (DMA), scanning electron microscopy (SEM) and change in weight, before and after hygrothermal exposure, are used to characterize the composites. Samples of plain epoxy 8552 are also exposed to the same aging conditions and characterized by optical microscopy (OM), FTIR spectroscopy and weight change. Stress-controlled tension-tension fatigue tests are then conducted using a stress ratio R = 0.1 and frequency of 5 Hz. The effects of hygrothermal aging on fatigue are interpreted by fatigue life diagrams as well as by studying evolution of Ply Crack density and delamination.
Brent Mccleave - One of the best experts on this subject based on the ideXlab platform.
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prediction of Ply Crack evolution and stiffness degradation in multidirectional symmetric laminates under multiaxial stress states
Composites Part B-engineering, 2018Co-Authors: John Montesano, Brent Mccleave, Chandra Veer SinghAbstract:Abstract A comprehensive study was performed to assess the influence of microscopic Ply Crack interactions on Crack surface opening (COD) and sliding displacements (CSD) for arbitrary plies in general symmetric multidirectional laminates under multiaxial stresses. Based on a generated database, general unified expressions for determining both CODs and CSDs at various Crack densities were developed and used with a multiscale damage-based model to predict stiffness degradation and Ply Crack evolution for cross-Ply, angle-Ply and quasi-isotropic laminates. The predicted elastic properties for laminates containing Cracks in individual plies, as well as simultaneous Cracks in multiple plies, were found to correlate well with data from independent finite element analysis, while Crack density predictions were validated with available experimental data. The developed unified expressions have increased the robustness and range of applicability of our damage-based multiscale model. Meanwhile, the ability of the model to predict simultaneous Cracking in multiple plies and both intra-Ply and inter-Ply Crack interactions for laminates under combines stresses is regarded as advantageous. The model can be invoked to efficiently predict Ply Crack evolution in laminates, and when combined with a suitable delamination model may be used as a design tool to assess the long-term durability of critical load-bearing structures.