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Wilfried Becker - One of the best experts on this subject based on the ideXlab platform.
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closed form analysis of interlaminar crack initiation in angle ply laminates
Composite Structures, 2021Co-Authors: Christopher Frey, Sebastian Dölling, Wilfried BeckerAbstract:Abstract The layerwise discontinuous stiffness properties in composite laminates may cause highly localized, singular concentrations of interlaminar stresses. These stress singularities occur in the vicinity of free edges and may induce interfacial cracks, often referred to as delaminations. Since conventional design processes, based on classical laminate plate theory, only consider inplane stress components, they do not cover the so-called Free-Edge Effect and the associated delamination onset and, therefore, disregard premature laminate failure. In the present study, interlaminar crack initiation in symmetric angle-ply laminates under tensile loading is investigated assuming the spontaneous formation of delaminations of finite length. A coupled stress and energy criterion is used requiring only two fundamental material parameters, the strength and the fracture toughness. The mechanical behaviour of the laminate is modeled by a highly efficient analytical closed-form approach providing results for the interlaminar shear stress in the interface and the energy release rates of potential cracks. The challenge of unknown interface fracture toughness is addressed by a parameter fit within physically reasonable limits. The resulting Effective failure loads are compared to experimental data and show the high potential of the coupled criterion on the one hand and of the proposed analytical model on the other hand.
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A scaled boundary finite element method model for interlaminar failure in composite laminates
Composite Structures, 2020Co-Authors: Sebastian Dölling, J. Hahn, Julian Felger, Sophia Bremm, Wilfried BeckerAbstract:Abstract Triggered by highly localized stress concentrations, failure of layered fibre-reinforced composites may occur in the form of an interface crack emanating from the laminate’s free edges. In the present work, this so-called Free-Edge Effect is examined using a scaled boundary finite element method (SBFEM) combined with a coupled stress and energy failure criterion. Focusing on symmetric angle-ply laminates, the SBFEM is formulated for a generalised plane strain state. This allows for a computationally efficient calculation of interface stresses as well as energy dissipation due to delamination of individual plies. For validation purposes, the SBFEM results are compared to analytical reference solutions based on the method of complex potentials. The Effective longitudinal stress at failure is determined by means of the coupled stress and energy criterion. The Effect of interface strength and toughness as well as the ply-thickness on the laminate’s failure stress are discussed in detail. Predictions are validated against experimental findings from literature for different laminate types and layups.
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Scaled Boundary Finite Element Analysis of three-dimensional crack configurations in laminate structures
2015Co-Authors: Sascha Hell, Wilfried BeckerAbstract:Laminate structures composed of fibre-reinforced plies typically are prone to the formation of inter-fiber cracks because of the given strongly anisotropic stiffness and strength properties. These inter-fiber cracks commonly run through complete plies but are stopped at the ply interfaces. Equally, such laminate structures are prone to the formation of delaminations, e.g. due to the Free-Edge Effect. An inter-fiber crack meeting a delamination forms a non-standard three-dimensional crack configuration with a locally singular stress field that should be investigated in regard of its criticality. For that purpose, the Scaled Boundary Finite Element Method turns out to be an appropriate and Effective analysis method that permits solving linear elastic mechanical problems including stress singularities with comparably little effort. Only the boundary is discretized by two-dimensional finite elements while the problem is considered analytically in the direction of the dimensionless radial coordinate ξ. A corresponding separation of variables representation for the displacement field employed in the virtual work equation leads to a system of differential equations of Cauchy-Euler type. This differential equation system can be converted into an eigenvalue problem and solved by standard eigenvalue solvers for non-symmetric matrices. By this kind of analysis, it is revealed that the considered three-dimensional crack configurations may go along with various unexpected non-standard stress singularities, namely singularities that are weaker than the well-known square root stress singularity in linear elastic fracture mechanics, but also singularities that are stronger and which may be called hypersingularities.
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interlaminar stress concentrations in layered structures part i a selective literature survey on the free edge Effect since 1967
Journal of Composite Materials, 2004Co-Authors: Christian Mittelstedt, Wilfried BeckerAbstract:Stress concentration phenomena in composite laminates are technically important situations. A well-known problem of this class is the Free-Edge Effect in composite laminates or as a superordinated example the stress concentrations in the vicinity of free laminate corners (so-called free-corner Effect). The present work is split into two parts. In the present contribution, after a short introduction to the given stress concentration problems in general we will survey relevant selected literature on the classical Free-Edge Effect dating from 1967 until today. Beside accentuation on approximate closed-form analytic methods for the stress analysis in the Free-Edge Effect situation, numerous references on numerical methods and investigations on the occurring stress singularities are also cited. In a subsequent paper we will present a simple closed-form method for the analysis of the stress fields in the vicinity of free laminate corners with arbitrary layup. The method is based on adequate stress shape assumpt...
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Free-Edge stress concentration in angle-ply laminates
Archive of Applied Mechanics, 1994Co-Authors: Wilfried BeckerAbstract:For a symmetric [±δ]s-angle-ply laminate coupon within the framework of linear elasticity the Free-Edge Effect is treated in a closed-form analytical way. To that end, for uniaxial tension the near-edge deformation is traced back to a complex-analytical potential. For the given boundary conditions the respective potential is determined and thus the resultant displacement field and the accompanying stresses. Thereby, in particular, a logarithmic singularity is obtained for the Free-Edge stress concentration.
Wieslaw K. Binienda - One of the best experts on this subject based on the ideXlab platform.
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Progressive Damage Simulation of Triaxially Braided Composite Using a 3D Meso-Scale Finite Element Model
Composite Structures, 2015Co-Authors: Chao Zhang, Wieslaw K. Binienda, Ning Li, Wenzhi Wang, Hongbing FangAbstract:Abstract This article proposes a fully three-dimensional finite element model, developed at the meso-scale level, to predict the progressive damage behavior of a single-layer triaxially braided composite subjected to tensile loading conditions. An anisotropic damage model is established by Murakami–Ohno damage theory to predict damage initiation and progression in the fiber tows. A traction–separation law has been applied to predict theoretically the progressive damage of fiber tow interfaces. The proposed model correlates well with experiment on both global stress–strain responses and local strain distributions. According to the damage contours at different global strain levels, the damage development of fiber tows and interlaminar delamination damage of interface are obtained, explicitly analyzed and correlated with experimental observations. The comparison of model prediction and experimental observations indicate that the model can accurately simulate the damage development of this composite material, i.e. fiber bundle splitting, interaction of Free-Edge Effect and delamination, and final failure of the specimen. This paper also discusses the role of material properties/parameters on the global responses through numerical parameter studies.
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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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Progressive Damage Simulation of Triaxially Braided Composite Using a 3D Meso-Scale Finite Element Model
Composite Structures, 2015Co-Authors: Chao Zhang, Wieslaw K. Binienda, Ning Li, Wenzhi Wang, Hongbing FangAbstract:Abstract This article proposes a fully three-dimensional finite element model, developed at the meso-scale level, to predict the progressive damage behavior of a single-layer triaxially braided composite subjected to tensile loading conditions. An anisotropic damage model is established by Murakami–Ohno damage theory to predict damage initiation and progression in the fiber tows. A traction–separation law has been applied to predict theoretically the progressive damage of fiber tow interfaces. The proposed model correlates well with experiment on both global stress–strain responses and local strain distributions. According to the damage contours at different global strain levels, the damage development of fiber tows and interlaminar delamination damage of interface are obtained, explicitly analyzed and correlated with experimental observations. The comparison of model prediction and experimental observations indicate that the model can accurately simulate the damage development of this composite material, i.e. fiber bundle splitting, interaction of Free-Edge Effect and delamination, and final failure of the specimen. This paper also discusses the role of material properties/parameters on the global responses through numerical parameter studies.
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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.
Sebastian Dölling - One of the best experts on this subject based on the ideXlab platform.
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closed form analysis of interlaminar crack initiation in angle ply laminates
Composite Structures, 2021Co-Authors: Christopher Frey, Sebastian Dölling, Wilfried BeckerAbstract:Abstract The layerwise discontinuous stiffness properties in composite laminates may cause highly localized, singular concentrations of interlaminar stresses. These stress singularities occur in the vicinity of free edges and may induce interfacial cracks, often referred to as delaminations. Since conventional design processes, based on classical laminate plate theory, only consider inplane stress components, they do not cover the so-called Free-Edge Effect and the associated delamination onset and, therefore, disregard premature laminate failure. In the present study, interlaminar crack initiation in symmetric angle-ply laminates under tensile loading is investigated assuming the spontaneous formation of delaminations of finite length. A coupled stress and energy criterion is used requiring only two fundamental material parameters, the strength and the fracture toughness. The mechanical behaviour of the laminate is modeled by a highly efficient analytical closed-form approach providing results for the interlaminar shear stress in the interface and the energy release rates of potential cracks. The challenge of unknown interface fracture toughness is addressed by a parameter fit within physically reasonable limits. The resulting Effective failure loads are compared to experimental data and show the high potential of the coupled criterion on the one hand and of the proposed analytical model on the other hand.
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A scaled boundary finite element method model for interlaminar failure in composite laminates
Composite Structures, 2020Co-Authors: Sebastian Dölling, J. Hahn, Julian Felger, Sophia Bremm, Wilfried BeckerAbstract:Abstract Triggered by highly localized stress concentrations, failure of layered fibre-reinforced composites may occur in the form of an interface crack emanating from the laminate’s free edges. In the present work, this so-called Free-Edge Effect is examined using a scaled boundary finite element method (SBFEM) combined with a coupled stress and energy failure criterion. Focusing on symmetric angle-ply laminates, the SBFEM is formulated for a generalised plane strain state. This allows for a computationally efficient calculation of interface stresses as well as energy dissipation due to delamination of individual plies. For validation purposes, the SBFEM results are compared to analytical reference solutions based on the method of complex potentials. The Effective longitudinal stress at failure is determined by means of the coupled stress and energy criterion. The Effect of interface strength and toughness as well as the ply-thickness on the laminate’s failure stress are discussed in detail. Predictions are validated against experimental findings from literature for different laminate types and layups.
Hongbing Fang - One of the best experts on this subject based on the ideXlab platform.
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Progressive Damage Simulation of Triaxially Braided Composite Using a 3D Meso-Scale Finite Element Model
Composite Structures, 2015Co-Authors: Chao Zhang, Wieslaw K. Binienda, Ning Li, Wenzhi Wang, Hongbing FangAbstract:Abstract This article proposes a fully three-dimensional finite element model, developed at the meso-scale level, to predict the progressive damage behavior of a single-layer triaxially braided composite subjected to tensile loading conditions. An anisotropic damage model is established by Murakami–Ohno damage theory to predict damage initiation and progression in the fiber tows. A traction–separation law has been applied to predict theoretically the progressive damage of fiber tow interfaces. The proposed model correlates well with experiment on both global stress–strain responses and local strain distributions. According to the damage contours at different global strain levels, the damage development of fiber tows and interlaminar delamination damage of interface are obtained, explicitly analyzed and correlated with experimental observations. The comparison of model prediction and experimental observations indicate that the model can accurately simulate the damage development of this composite material, i.e. fiber bundle splitting, interaction of Free-Edge Effect and delamination, and final failure of the specimen. This paper also discusses the role of material properties/parameters on the global responses through numerical parameter studies.
