L'élaboration de structures primaires en matériau composite destinées à la production d'aéronefs ... more L'élaboration de structures primaires en matériau composite destinées à la production d'aéronefs est soumise à un contrôle qualité strict (contrôles non destructifs sur pièces et destructifs sur éprouvettes représentatives). Cette étape permet de valider le matériau mis en oeuvre ainsi que le bon déroulement du processus de moulage. Pour ce faire, il existe plusieurs méthodes d'analyse, chacune d'elles présente un certain nombre d'avantages mais aussi des inconvénients.
Most critical processing step during long fiber reinforced epoxy matrix composite laminate manufa... more Most critical processing step during long fiber reinforced epoxy matrix composite laminate manufacturing is the polymerization stage. If not optimized, it gives birth to defects in the bulk material, such as voids. These defects are considered as possible sources of damage in the composite parts. The aim of this work is to model the evolution of void growth in thermoset composite laminates after ply collation (autoclave processes) or resin impregnation (RTM, LCM process). A coupled mechanical and diffusion model is presented to better predict the final void size at the end of polymerization. Amongst the parameter investigated, onset of pressure application and diffusive species concentration where found to have a major effect on void size evolution during curing process.
OATAO is an open access repository that collects the work of Toulouse researchers and makes it fr... more OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author -deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID: 4339 To link to this article: To cite this version: TRABELSI Walid, MICHEL Laurent, OTHOMENE Renaud. Effects of stitching on delamination of satin weave carbon-epoxy laminates under mode I, mode II and mixed-mode I/II loadings. Abstract The objective of the present study is to characterize the effect of modified chain stitching on the delamination growth under mixed-mode I/II loading conditions. Delamination toughness under mode I is experimentally determined, for unstitched and stitched laminates, by using untabbed and tabbed double cantilever beam (TDCB) tests. The effect of the reinforcing tabs on mode I toughness is investigated. Stitching improves the energy release rate (ERR) up to 4 times in mode I. Mode II delamination toughness is evaluated in end-notched flexure (ENF) tests. Different geometries of stitched specimens are tested. Crack propagation occurs without any failure of stitching yarns. The final crack length attains the mid-span or it stops before and the specimen breaks in bending. The ERR is initially low and gradually increases with crack length to very high values. The mixed-mode delamination behaviour is investigated using a mixed-mode bending (MMB) test. For unstitched specimens, a simple mixed-mode criterion is identified. For stitched specimens, stitching yarns do not break during 25% of mode I ratio tests and the ERR increase is relatively small compared to unstitched values. For 70% and 50% of mode I ratios, failures of yarns are observed during crack propagation and tests are able to capture correctly the effect of the stitching: it clearly improves the ERR for these two mixed modes, as much as threefold.
ABSTRACT The Low through-the-Thickness Strengths of Composites make them Prone to Delamination an... more ABSTRACT The Low through-the-Thickness Strengths of Composites make them Prone to Delamination and Brutal Rupture. for Primary Aircraft Structural Components, it is Necessary to Predict Failure with Adequate Criteria for any Structure of Various Thicknesses and in Zones of Material or Geometric Discontinuities. the Purpose of the Present Work is to Evaluate the Ability of our Continuous Damage Model to Predict at which Interface Delamination will Occur in any Geometrical or Material Configuration. Numerical Predictions of Delamination Onset Computed by our CDM Model Show a Good Agreement with Theoretical Estimations and Experimental Results of an L-Shape Structure Reference Case. Comparisons between 2D and 3D Models Show no Effect of Free Boundaries on Delamination Onset and Growth.
ABSTRACT The composite materials are nowadays widely used in aeronautical domain. These materials... more ABSTRACT The composite materials are nowadays widely used in aeronautical domain. These materials are subjected to different types of loading that can damage a part of the structure. This diminishes the resistance of the structure to failure. In this paper, matrix cracking and delamination propagation in composite laminates are simulated as a part of damage. Two different computational strategies are developed: (i) a cohesive model (CM) based on the classical continuum mechanics and (ii) a continuous damage material model (CDM) coupling failure modes and damage. Another mixed methodology (MM) is proposed using the continuous damage model for delamination initiation and the cohesive model for 3D crack propagation and mesh openings. A good agreement was obtained when compared simple characterization tests and corresponding simulations.
ABSTRACT Aeronautic Certification rules established for the metallic materials are not convenient... more ABSTRACT Aeronautic Certification rules established for the metallic materials are not convenient for the composite structures concerning the resistance against impact. The computer-based design is a new methodology that is thought about to replace the experimental tests. It becomes necessary for numerical methods to be robust and predictive for impact. Three questions are addressed in this study: (i) can a numerical model be “mechanically intrinsic” to predict damage after impact, (ii) can this model be the same for a lab sample and a large structure, and (iii) can the numerical model be predictive enough to predict the Compression After Impact (CAI)? Three different computational strategies are used and compared: a Cohesive Model (CM), a Continuous Damage Model (CDM) coupling failure modes and damage, and a Mixed Methodology (MM) using the CDM for delamination initiation and the CM for cracks propagation. The first attempts to use the Smooth Particle Hydrodynamics method are presented. Finally, impact on a fuselage is modelled and a numerical two-stage strategy is developed to predict the CAI.
L'élaboration de structures primaires en matériau composite destinées à la production d'aéronefs ... more L'élaboration de structures primaires en matériau composite destinées à la production d'aéronefs est soumise à un contrôle qualité strict (contrôles non destructifs sur pièces et destructifs sur éprouvettes représentatives). Cette étape permet de valider le matériau mis en oeuvre ainsi que le bon déroulement du processus de moulage. Pour ce faire, il existe plusieurs méthodes d'analyse, chacune d'elles présente un certain nombre d'avantages mais aussi des inconvénients.
Most critical processing step during long fiber reinforced epoxy matrix composite laminate manufa... more Most critical processing step during long fiber reinforced epoxy matrix composite laminate manufacturing is the polymerization stage. If not optimized, it gives birth to defects in the bulk material, such as voids. These defects are considered as possible sources of damage in the composite parts. The aim of this work is to model the evolution of void growth in thermoset composite laminates after ply collation (autoclave processes) or resin impregnation (RTM, LCM process). A coupled mechanical and diffusion model is presented to better predict the final void size at the end of polymerization. Amongst the parameter investigated, onset of pressure application and diffusive species concentration where found to have a major effect on void size evolution during curing process.
OATAO is an open access repository that collects the work of Toulouse researchers and makes it fr... more OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author -deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID: 4339 To link to this article: To cite this version: TRABELSI Walid, MICHEL Laurent, OTHOMENE Renaud. Effects of stitching on delamination of satin weave carbon-epoxy laminates under mode I, mode II and mixed-mode I/II loadings. Abstract The objective of the present study is to characterize the effect of modified chain stitching on the delamination growth under mixed-mode I/II loading conditions. Delamination toughness under mode I is experimentally determined, for unstitched and stitched laminates, by using untabbed and tabbed double cantilever beam (TDCB) tests. The effect of the reinforcing tabs on mode I toughness is investigated. Stitching improves the energy release rate (ERR) up to 4 times in mode I. Mode II delamination toughness is evaluated in end-notched flexure (ENF) tests. Different geometries of stitched specimens are tested. Crack propagation occurs without any failure of stitching yarns. The final crack length attains the mid-span or it stops before and the specimen breaks in bending. The ERR is initially low and gradually increases with crack length to very high values. The mixed-mode delamination behaviour is investigated using a mixed-mode bending (MMB) test. For unstitched specimens, a simple mixed-mode criterion is identified. For stitched specimens, stitching yarns do not break during 25% of mode I ratio tests and the ERR increase is relatively small compared to unstitched values. For 70% and 50% of mode I ratios, failures of yarns are observed during crack propagation and tests are able to capture correctly the effect of the stitching: it clearly improves the ERR for these two mixed modes, as much as threefold.
ABSTRACT The Low through-the-Thickness Strengths of Composites make them Prone to Delamination an... more ABSTRACT The Low through-the-Thickness Strengths of Composites make them Prone to Delamination and Brutal Rupture. for Primary Aircraft Structural Components, it is Necessary to Predict Failure with Adequate Criteria for any Structure of Various Thicknesses and in Zones of Material or Geometric Discontinuities. the Purpose of the Present Work is to Evaluate the Ability of our Continuous Damage Model to Predict at which Interface Delamination will Occur in any Geometrical or Material Configuration. Numerical Predictions of Delamination Onset Computed by our CDM Model Show a Good Agreement with Theoretical Estimations and Experimental Results of an L-Shape Structure Reference Case. Comparisons between 2D and 3D Models Show no Effect of Free Boundaries on Delamination Onset and Growth.
ABSTRACT The composite materials are nowadays widely used in aeronautical domain. These materials... more ABSTRACT The composite materials are nowadays widely used in aeronautical domain. These materials are subjected to different types of loading that can damage a part of the structure. This diminishes the resistance of the structure to failure. In this paper, matrix cracking and delamination propagation in composite laminates are simulated as a part of damage. Two different computational strategies are developed: (i) a cohesive model (CM) based on the classical continuum mechanics and (ii) a continuous damage material model (CDM) coupling failure modes and damage. Another mixed methodology (MM) is proposed using the continuous damage model for delamination initiation and the cohesive model for 3D crack propagation and mesh openings. A good agreement was obtained when compared simple characterization tests and corresponding simulations.
ABSTRACT Aeronautic Certification rules established for the metallic materials are not convenient... more ABSTRACT Aeronautic Certification rules established for the metallic materials are not convenient for the composite structures concerning the resistance against impact. The computer-based design is a new methodology that is thought about to replace the experimental tests. It becomes necessary for numerical methods to be robust and predictive for impact. Three questions are addressed in this study: (i) can a numerical model be “mechanically intrinsic” to predict damage after impact, (ii) can this model be the same for a lab sample and a large structure, and (iii) can the numerical model be predictive enough to predict the Compression After Impact (CAI)? Three different computational strategies are used and compared: a Cohesive Model (CM), a Continuous Damage Model (CDM) coupling failure modes and damage, and a Mixed Methodology (MM) using the CDM for delamination initiation and the CM for cracks propagation. The first attempts to use the Smooth Particle Hydrodynamics method are presented. Finally, impact on a fuselage is modelled and a numerical two-stage strategy is developed to predict the CAI.
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