The Experts below are selected from a list of 64824 Experts worldwide ranked by ideXlab platform
Robert K. Goldberg - One of the best experts on this subject based on the ideXlab platform.
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The influence of interlaminar microstructure on micro-cracking at laminate Free Edge
Composites Part A: Applied Science and Manufacturing, 2018Co-Authors: Christopher R. Cater, Xinran Xiao, Robert K. Goldberg, Xiaojing GongAbstract:To investigate the influence of interlaminar microstructure on micro-cracking at the Free Edge of a laminate, a two-scale finite element modelling approach has been developed and used to examine the 90/90 interface in [25(N)/-25(N)/90(N)](s) laminates. The current paper extends the analysis to the -25/90 interface. The results are compared with that of the 90/90 interface. The results show that, like the 90/90 interface, the micro-scale matrix stress at the Free Edge is sensitive to the interlaminar microstructure. Increasing the resin content resulted in the matrix stress increasing during thermal cooldown, but reducing under tensile loading. However, the site of the maximum matrix stress was different. The results suggest that manufacturing induced pre-cracks may not coincide with the sites of progressive cracking under service loadings. The analysis provides new insights into the micro-cracking and damage evolution observed in experiments.
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Multiscale investigation of micro-scale stresses at composite laminate Free Edge
Composite Structures, 2018Co-Authors: Christopher R. Cater, Xinran Xiao, Robert K. Goldberg, Xiaojing GongAbstract:The Free Edge effect is well understood at the laminate and lamina scale. The influence of the microstructure on micro-scale stresses and Free Edge cracking, however, is less known. This work aims at a better understanding of the effect of microscopic features on micro-scale stresses and the tendency of initial micro-cracking at the laminate Free Edge. To this end, a two-scale finite element (FE) modelling approach is developed. It consists of a meso-scale model to capture the laminate stacking sequence and the global stress field under a given loading condition, and a micro-scale model to predict the local constituent level stresses at the Free Edge. The two models were coupled one-way through a strain localization rule. A procedure to determine the boundary conditions for micro-scale FE models containing a Free Edge was proposed. The model was used to examine the 90/90 interface in [25N/−25N/90N]S IM7/8552 carbon/epoxy composite laminates. The effects of thermal and tensile loading were investigated independently to understand the influence of the interlaminar microstructure on micro-scale stresses at Free Edges during manufacture and under mechanical loading. The results agreed with the trend of Free Edge pre-cracks and progressive damage observed in experiments.
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Multiscale Investigation of Micro-Cracking at Composite Laminate Free Edge
American Society for Composites 2017, 2017Co-Authors: Christopher R. Cater, Xinran Xiao, Robert K. Goldberg, Xiaojing GongAbstract:To investigate the effect of microscopic features on initial micro-cracking at the laminate Free Edge, a two-scale finite element (FE) modelling approach is proposed. It consists of a meso-scale model to capture the laminate stacking sequence and the global stress field under a given loading condition, and a micro-scale model to predict the local constituent level stresses at the Free Edge. The two models are coupled oneway through a strain localization rule. A procedure to determine the boundary conditions for micro-scale FE models containing a Free Edge has been developed. The model developed this way was used to examine the 90/90 interface in [25N/-25N/90N]S composite laminates. The effects of thermal and tensile loading were investigated separately to understand the influence of interlaminar microstructure on micro-scale stresses at laminate Free Edges during manufacture and under mechanical loading. The results agreed with the trend of Free Edge pre-cracks and progressive damage observed in experiments.
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Free-Edge effect on the effective stiffness of single-layer triaxially braided composite
Composites Science and Technology, 2015Co-Authors: Chao Zhang, Wieslaw K. Binienda, Robert K. GoldbergAbstract:Abstract Free-Edge effect is known to play an important role in the failure of triaxially braided composites, especially under transverse tension loading conditions. However, there is little understanding available regarding the Free-Edge effect on the elastic property of the material. The emphasis of the present study is to examine the impact of the Free-Edge effect on the effective elastic response of a single-layer triaxially braided composite. Transverse tension straight-sided coupon specimens with various widths are tested and analyzed. The experimental results demonstrate an obvious increase in the tangent modulus and failure strength as the specimen width increases. The surface out-of-plane displacement contours present a continuous out-of-plane warping behavior distributed periodically along the Free Edges in an antisymmetric way. A meso-scale finite element model is utilized to study the coupon specimens; it is found to correlate well with the experimental data in predicting elastic properties and out-of-plane warping behavior. The results indicate that Free-Edge effect is an inherent factor of the antisymmetric braided architecture of bias fiber bundles. By conducting a dimensional analysis, the relationships between effective moduli and specimen width are quantified using Weibull equations; this method could potentially be used to predict the material properties of large structural components using small-scale test data.
Naveen Sivadasan - One of the best experts on this subject based on the ideXlab platform.
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on polynomial kernelization of mathcal Free Edge deletion
Algorithmica, 2017Co-Authors: N. R. Aravind, R. B. Sandeep, Naveen SivadasanAbstract:For a set \(\mathcal {H}\) of graphs, the \(\mathcal {H}\)-Free Edge Deletion problem is to decide whether there exist at most k Edges in the input graph, for some \(k\in \mathbb {N}\), whose deletion results in a graph without an induced copy of any of the graphs in \(\mathcal {H}\) . The problem is known to be fixed-parameter tractable if \(\mathcal {H}\) is of finite cardinality. In this paper, we present a polynomial kernel for this problem for any fixed finite set \(\mathcal {H}\) of connected graphs for the case where the input graphs are of bounded degree. We use a single kernelization rule which deletes vertices ‘far away’ from the induced copies of every \(H\in \mathcal {H}\) in the input graph. With a slightly modified kernelization rule, we obtain polynomial kernels for \(\mathcal {H}\)-Free Edge Deletion under the following three settings: \(\mathcal {H}\) contains \(K_{1,s}\) and \(K_t\); \(\mathcal {H}\) contains \(K_{1,s}\) and the input graphs are \(K_t\)-Free; \(\mathcal {H}\) contains \(K_{t}\) and the input graphs are \(K_{1,s}\)-Free; where \(s>1\) and \(t>2\) are any fixed integers. Our result provides the first polynomial kernels for Claw-Free Edge Deletion and Line Edge Deletion for \(K_t\)-Free input graphs which are known to be NP-complete even for \(K_4\)-Free graphs.
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Dichotomy Results on the Hardness of $H$-Free Edge Modification Problems
SIAM Journal on Discrete Mathematics, 2017Co-Authors: N. R. Aravind, R. B. Sandeep, Naveen SivadasanAbstract:For a graph $H$, the $H$-Free Edge Deletion problem asks whether there exist at most $k$ Edges whose deletion from the input graph $G$ results in a graph without any induced copy of $H$. $H$-Free Edge Completion and $H$-Free Edge Editing are defined similarly where only completion (addition) of Edges are allowed in the former and both completion and deletion are allowed in the latter. We completely settle the classical complexities of these problems by proving that $H$-Free Edge Deletion is NP-complete if and only if $H$ is a graph with at least two Edges, $H$-Free Edge Completion is NP-complete if and only if $H$ is a graph with at least two nonEdges, and $H$-Free Edge Editing is NP-complete if and only if $H$ is a graph with at least three vertices. Our result on $H$-Free Edge Editing resolves a conjecture by Alon and Stav [Theoret. Comput. Sci., 2009, pp. 4920--4927]. Additionally, we prove that these NP-complete problems cannot be solved in parameterized subexponential time, i.e., in time $2^{o(k)}\cd...
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On Polynomial Kernelization of $$\mathcal {}$$- Free Edge Deletion
Algorithmica, 2016Co-Authors: N. R. Aravind, R. B. Sandeep, Naveen SivadasanAbstract:For a set \(\mathcal {H}\) of graphs, the \(\mathcal {H}\)-Free Edge Deletion problem is to decide whether there exist at most k Edges in the input graph, for some \(k\in \mathbb {N}\), whose deletion results in a graph without an induced copy of any of the graphs in \(\mathcal {H}\) . The problem is known to be fixed-parameter tractable if \(\mathcal {H}\) is of finite cardinality. In this paper, we present a polynomial kernel for this problem for any fixed finite set \(\mathcal {H}\) of connected graphs for the case where the input graphs are of bounded degree. We use a single kernelization rule which deletes vertices ‘far away’ from the induced copies of every \(H\in \mathcal {H}\) in the input graph. With a slightly modified kernelization rule, we obtain polynomial kernels for \(\mathcal {H}\)-Free Edge Deletion under the following three settings: \(\mathcal {H}\) contains \(K_{1,s}\) and \(K_t\); \(\mathcal {H}\) contains \(K_{1,s}\) and the input graphs are \(K_t\)-Free; \(\mathcal {H}\) contains \(K_{t}\) and the input graphs are \(K_{1,s}\)-Free; where \(s>1\) and \(t>2\) are any fixed integers. Our result provides the first polynomial kernels for Claw-Free Edge Deletion and Line Edge Deletion for \(K_t\)-Free input graphs which are known to be NP-complete even for \(K_4\)-Free graphs.
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parameterized lower bounds and dichotomy results for the np completeness of h Free Edge modification problems
Latin American Symposium on Theoretical Informatics, 2016Co-Authors: N. R. Aravind, R. B. Sandeep, Naveen SivadasanAbstract:For a graph H, the \(H\)-Free Edge Deletion problem asks whether there exist at most k Edges whose deletion from the input graph G results in a graph without any induced copy of H. \(H\)-Free Edge Completion and \(H\)-Free Edge Editing are defined similarly where only completion (addition) of Edges are allowed in the former and both completion and deletion are allowed in the latter. We completely settle the classical complexities of these problems by proving that \(H\)-Free Edge Deletion is NP-complete if and only if H is a graph with at least two Edges, \(H\)-Free Edge Completion is NP-complete if and only if H is a graph with at least two non-Edges and \(H\)-Free Edge Editing is NP-complete if and only if H is a graph with at least three vertices. Our result on \(H\)-Free Edge Editing resolves a conjecture by Alon and Stav (2009). Additionally, we prove that, these NP-complete problems cannot be solved in parameterized subexponential time, i.e., in time \(2^{o(k)}\cdot |G|^{O(1)}\), unless Exponential Time Hypothesis fails. Furthermore, we obtain implications on the incompressibility of these problems.
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LATIN - Parameterized Lower Bounds and Dichotomy Results for the NP-completeness of H-Free Edge Modification Problems
LATIN 2016: Theoretical Informatics, 2016Co-Authors: N. R. Aravind, R. B. Sandeep, Naveen SivadasanAbstract:For a graph H, the \(H\)-Free Edge Deletion problem asks whether there exist at most k Edges whose deletion from the input graph G results in a graph without any induced copy of H. \(H\)-Free Edge Completion and \(H\)-Free Edge Editing are defined similarly where only completion (addition) of Edges are allowed in the former and both completion and deletion are allowed in the latter. We completely settle the classical complexities of these problems by proving that \(H\)-Free Edge Deletion is NP-complete if and only if H is a graph with at least two Edges, \(H\)-Free Edge Completion is NP-complete if and only if H is a graph with at least two non-Edges and \(H\)-Free Edge Editing is NP-complete if and only if H is a graph with at least three vertices. Our result on \(H\)-Free Edge Editing resolves a conjecture by Alon and Stav (2009). Additionally, we prove that, these NP-complete problems cannot be solved in parameterized subexponential time, i.e., in time \(2^{o(k)}\cdot |G|^{O(1)}\), unless Exponential Time Hypothesis fails. Furthermore, we obtain implications on the incompressibility of these problems.
Xiaojing Gong - One of the best experts on this subject based on the ideXlab platform.
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The influence of interlaminar microstructure on micro-cracking at laminate Free Edge
Composites Part A: Applied Science and Manufacturing, 2018Co-Authors: Christopher R. Cater, Xinran Xiao, Robert K. Goldberg, Xiaojing GongAbstract:To investigate the influence of interlaminar microstructure on micro-cracking at the Free Edge of a laminate, a two-scale finite element modelling approach has been developed and used to examine the 90/90 interface in [25(N)/-25(N)/90(N)](s) laminates. The current paper extends the analysis to the -25/90 interface. The results are compared with that of the 90/90 interface. The results show that, like the 90/90 interface, the micro-scale matrix stress at the Free Edge is sensitive to the interlaminar microstructure. Increasing the resin content resulted in the matrix stress increasing during thermal cooldown, but reducing under tensile loading. However, the site of the maximum matrix stress was different. The results suggest that manufacturing induced pre-cracks may not coincide with the sites of progressive cracking under service loadings. The analysis provides new insights into the micro-cracking and damage evolution observed in experiments.
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Multiscale investigation of micro-scale stresses at composite laminate Free Edge
Composite Structures, 2018Co-Authors: Christopher R. Cater, Xinran Xiao, Robert K. Goldberg, Xiaojing GongAbstract:The Free Edge effect is well understood at the laminate and lamina scale. The influence of the microstructure on micro-scale stresses and Free Edge cracking, however, is less known. This work aims at a better understanding of the effect of microscopic features on micro-scale stresses and the tendency of initial micro-cracking at the laminate Free Edge. To this end, a two-scale finite element (FE) modelling approach is developed. It consists of a meso-scale model to capture the laminate stacking sequence and the global stress field under a given loading condition, and a micro-scale model to predict the local constituent level stresses at the Free Edge. The two models were coupled one-way through a strain localization rule. A procedure to determine the boundary conditions for micro-scale FE models containing a Free Edge was proposed. The model was used to examine the 90/90 interface in [25N/−25N/90N]S IM7/8552 carbon/epoxy composite laminates. The effects of thermal and tensile loading were investigated independently to understand the influence of the interlaminar microstructure on micro-scale stresses at Free Edges during manufacture and under mechanical loading. The results agreed with the trend of Free Edge pre-cracks and progressive damage observed in experiments.
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Multiscale Investigation of Micro-Cracking at Composite Laminate Free Edge
American Society for Composites 2017, 2017Co-Authors: Christopher R. Cater, Xinran Xiao, Robert K. Goldberg, Xiaojing GongAbstract:To investigate the effect of microscopic features on initial micro-cracking at the laminate Free Edge, a two-scale finite element (FE) modelling approach is proposed. It consists of a meso-scale model to capture the laminate stacking sequence and the global stress field under a given loading condition, and a micro-scale model to predict the local constituent level stresses at the Free Edge. The two models are coupled oneway through a strain localization rule. A procedure to determine the boundary conditions for micro-scale FE models containing a Free Edge has been developed. The model developed this way was used to examine the 90/90 interface in [25N/-25N/90N]S composite laminates. The effects of thermal and tensile loading were investigated separately to understand the influence of interlaminar microstructure on micro-scale stresses at laminate Free Edges during manufacture and under mechanical loading. The results agreed with the trend of Free Edge pre-cracks and progressive damage observed in experiments.
Wieslaw K. Binienda - One of the best experts on this subject based on the ideXlab platform.
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Free-Edge effect on the effective stiffness of single-layer triaxially braided composite
Composites Science and Technology, 2015Co-Authors: Chao Zhang, Wieslaw K. Binienda, Robert K. GoldbergAbstract:Abstract Free-Edge effect is known to play an important role in the failure of triaxially braided composites, especially under transverse tension loading conditions. However, there is little understanding available regarding the Free-Edge effect on the elastic property of the material. The emphasis of the present study is to examine the impact of the Free-Edge effect on the effective elastic response of a single-layer triaxially braided composite. Transverse tension straight-sided coupon specimens with various widths are tested and analyzed. The experimental results demonstrate an obvious increase in the tangent modulus and failure strength as the specimen width increases. The surface out-of-plane displacement contours present a continuous out-of-plane warping behavior distributed periodically along the Free Edges in an antisymmetric way. A meso-scale finite element model is utilized to study the coupon specimens; it is found to correlate well with the experimental data in predicting elastic properties and out-of-plane warping behavior. The results indicate that Free-Edge effect is an inherent factor of the antisymmetric braided architecture of bias fiber bundles. By conducting a dimensional analysis, the relationships between effective moduli and specimen width are quantified using Weibull equations; this method could potentially be used to predict the material properties of large structural components using small-scale test data.
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Numerical Analysis of Free-Edge Effect on Size-Influenced Mechanical Properties of Single-Layer Triaxially Braided Composites
Applied Composite Materials, 2014Co-Authors: Chao Zhang, Wieslaw K. BiniendaAbstract:The mechanical properties of triaxially braided composites under transverse loads are found to be size-dependent, due to the presence of Free-Edge effect. Numerical studies of the mechanical behaviors of straight-sided coupon specimens and an infinitely large plate under both axial and transverse tension loads were conducted using a meso-scale finite element model. The numerical model correlates well with experimental results, successfully capturing the Free-Edge warping phenomena under transverse tension. Free-Edge effect is observed as out-of-plane warping, and it can be correlated to the premature damage initiation in the affected area. The numerical results characterize the impact of Free-Edge effects on the global stress–strain response and local failure mechanisms. By conducting dimensional analysis, the relationships of effective stiffness and strength against specimen width are quantified using Weibull equations. The results of this study indicate that the Free-Edge effect is an inherent behavior of braided architecture. The Free-Edge effect produces significantly reduced transverse tension modulus and strength measurements.
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a meso scale finite element model for simulating Free Edge effect in carbon epoxy textile composite
Mechanics of Materials, 2014Co-Authors: Chao Zhang, Wieslaw K. BiniendaAbstract:Abstract Textile composites are well known for their excellent through thickness properties and impact resistance. In this study, a representative unit cell model of a triaxial braided composite is developed based on the composite fiber volume ratio, specimen thickness and microscopic image analysis. A meso-scale finite element (FE) mesh is generated based on the detailed unit cell dimensions and fiber bundle geometry parameters. The fiber bundles are modeled as unidirectional fiber reinforced composites. A micromechanical finite element model was developed to predict the elastic and strength material properties of each unidirectional composite by imposing correct boundary conditions that can simulate the actual deformation within the braided composite. These details are then applied in the meso-mechanical finite element model for a 0°/+60°/−60° triaxially braided T700s/E862 carbon/epoxy composite. Model correlations are conducted by comparing numerical predicted and experimental measured axial tension and transverse tension response of a straight-sided, single-layer (one ply thick) coupon. By applying a periodic boundary condition in the loading direction, the meso model captures the local damage initiation and global failure behavior, as well as the periodic Free-Edge warping effect. The failure mechanisms are studied using the field damage initiation contours and local stress history. The influence of Free-Edge effect on the failure behaviors is investigated. The numerical study results reveal that this meso model is capable of predicting Free-Edge effect and allows identification of its impact on the composite response.
Chao Zhang - One of the best experts on this subject based on the ideXlab platform.
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Free-Edge effect on the effective stiffness of single-layer triaxially braided composite
Composites Science and Technology, 2015Co-Authors: Chao Zhang, Wieslaw K. Binienda, Robert K. GoldbergAbstract:Abstract Free-Edge effect is known to play an important role in the failure of triaxially braided composites, especially under transverse tension loading conditions. However, there is little understanding available regarding the Free-Edge effect on the elastic property of the material. The emphasis of the present study is to examine the impact of the Free-Edge effect on the effective elastic response of a single-layer triaxially braided composite. Transverse tension straight-sided coupon specimens with various widths are tested and analyzed. The experimental results demonstrate an obvious increase in the tangent modulus and failure strength as the specimen width increases. The surface out-of-plane displacement contours present a continuous out-of-plane warping behavior distributed periodically along the Free Edges in an antisymmetric way. A meso-scale finite element model is utilized to study the coupon specimens; it is found to correlate well with the experimental data in predicting elastic properties and out-of-plane warping behavior. The results indicate that Free-Edge effect is an inherent factor of the antisymmetric braided architecture of bias fiber bundles. By conducting a dimensional analysis, the relationships between effective moduli and specimen width are quantified using Weibull equations; this method could potentially be used to predict the material properties of large structural components using small-scale test data.
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Numerical Analysis of Free-Edge Effect on Size-Influenced Mechanical Properties of Single-Layer Triaxially Braided Composites
Applied Composite Materials, 2014Co-Authors: Chao Zhang, Wieslaw K. BiniendaAbstract:The mechanical properties of triaxially braided composites under transverse loads are found to be size-dependent, due to the presence of Free-Edge effect. Numerical studies of the mechanical behaviors of straight-sided coupon specimens and an infinitely large plate under both axial and transverse tension loads were conducted using a meso-scale finite element model. The numerical model correlates well with experimental results, successfully capturing the Free-Edge warping phenomena under transverse tension. Free-Edge effect is observed as out-of-plane warping, and it can be correlated to the premature damage initiation in the affected area. The numerical results characterize the impact of Free-Edge effects on the global stress–strain response and local failure mechanisms. By conducting dimensional analysis, the relationships of effective stiffness and strength against specimen width are quantified using Weibull equations. The results of this study indicate that the Free-Edge effect is an inherent behavior of braided architecture. The Free-Edge effect produces significantly reduced transverse tension modulus and strength measurements.
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a meso scale finite element model for simulating Free Edge effect in carbon epoxy textile composite
Mechanics of Materials, 2014Co-Authors: Chao Zhang, Wieslaw K. BiniendaAbstract:Abstract Textile composites are well known for their excellent through thickness properties and impact resistance. In this study, a representative unit cell model of a triaxial braided composite is developed based on the composite fiber volume ratio, specimen thickness and microscopic image analysis. A meso-scale finite element (FE) mesh is generated based on the detailed unit cell dimensions and fiber bundle geometry parameters. The fiber bundles are modeled as unidirectional fiber reinforced composites. A micromechanical finite element model was developed to predict the elastic and strength material properties of each unidirectional composite by imposing correct boundary conditions that can simulate the actual deformation within the braided composite. These details are then applied in the meso-mechanical finite element model for a 0°/+60°/−60° triaxially braided T700s/E862 carbon/epoxy composite. Model correlations are conducted by comparing numerical predicted and experimental measured axial tension and transverse tension response of a straight-sided, single-layer (one ply thick) coupon. By applying a periodic boundary condition in the loading direction, the meso model captures the local damage initiation and global failure behavior, as well as the periodic Free-Edge warping effect. The failure mechanisms are studied using the field damage initiation contours and local stress history. The influence of Free-Edge effect on the failure behaviors is investigated. The numerical study results reveal that this meso model is capable of predicting Free-Edge effect and allows identification of its impact on the composite response.
