This work investigates the hygrothermal cyclic aging of epoxy-based bonded assemblies. The focus is given here to severe long-term environmental conditions. The aging procedure is performed between ...70° C with a relative humidity of 90% and −40° C without humidity, over a cyclic period of 12 h and for a total exposure time of 2 months. The aim of this study is to highlight the consequences of such hygrothermal aging on physico-chemical and mechanical parameters at both the material scale (adhesive) and the structural scale (bonded assemblies). Evolution of water absorption and glass transition temperature with aging cycles are monitored on adhesive bulk specimens by gravimetric analysis and DSC analysis respectively. The evolution of the quasi-static mechanical behavior, strength and elongation at failure, is characterized on adhesive massive specimens and on Single Lap Joint assemblies. Results show a progressive and important degradation of physico-chemical and mechanical properties with the number of cycles, of greater amount than that observed during static aging (loss of SLJ strength by 30% after 56 aging days; loss of the adhesive
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by 45% for around 5% water uptake after aging 21 days). This behavior is related with an embrittling effect at the adhesive scale very specific to water change of state involved in these aging conditions. This combined analysis at different scales ensures a deep understanding of physico-chemical phenomena induced by hygrothermal aging and provides significant information for the further modeling of bonded joints assemblies.
•Post-impact damage propagation in tension in woven carbon/epoxy laminates is studied.•The monitoring of damages is based on Digital Image Correlation and RX Tomography.•The propagation of cracks is ...governed by the resin damages and by delamination.•A FEM based on Semi-Continuous strategy is developed to represent these propagations.•This new modelling strategy well represent the damage initiation and propagation.
This article concerns the experimental and numerical study of post-impact damage propagation in thin carbon/epoxy woven composite laminates loaded in fatigue tension. Low velocity normal drop weight impact tests are first performed. Post-impact fatigue tensile tests are then carried out. They are controlled in displacement. The monitoring is based on Digital Image Correlation and RX tomography. The influence of the impact energy and the tensile fatigue loading on the post-impact damage propagation is studied. The damage propagation is governed by matrix damage, with the emergence of tows/resin splittings and intra-tows crackings as well as delamination when the plies have different orientations. When the impact energy or the displacement level increases, the post-impact damage initiates sooner and propagate faster. In some cases, that can lead to a quasi-instantaneous failure identical to that observed for quasi-static tensile loading. The FEM based semi-continuous approach, initialy developped for the modelling of impact damage, is extended to fatigue loading for carbon/epoxy woven laminates. Fatigue damage laws, based on experimental observations are implemented. The modelling well correlates the experimental results in terms of damage propagation scenario and speed depending on the number of cycles for laminates made up of plies with the same orientation.
This article concerns the experimental study of post-impact damage propagation in two thin carbon/epoxy and glass/epoxy hybrid woven composite laminates loaded in fatigue tension. Low velocity normal ...drop weight impact tests are first performed. Post-impact fatigue tensile tests are then carried out. They are controlled in displacement. The damage propagation is monitored by RX Tomography and Digital Image Correlation. The influence of the impact energy and the displacement level variation on the post-impact damage propagation is studied. Post-impact fatigue tests are also conducted on thin carbon/epoxy and glass/epoxy mono-material woven composite laminates in order to understand the phenomenons which occur in the hybrid laminates. Two different behaviours depending on the hybrid configuration are obtained. The post-impact damage propagation in fatigue is mainly influenced by the carbon plies orientations. Levels of loading and impact energies have an influence on the initiation of the damage propagation and on the speed. They have also an influence of the damage propagation scenario when delamination occurs. The influence of the stacking sequence is also studied. The change of the carbon plies position in the hybrid laminate leads to a change of the post-impact fatigue behaviour.
This article concerns the modelling of post-impact damage propagation in thin carbon/epoxy and glass/epoxy hybrid woven composite laminates loaded in fatigue tension. The modelling is based on the ...semi-continuous approach implemented into the explicit finite element code RADIOSS. The bundles are modelled with rod elements and the resin is modeled with a specific damageable shell element, used to stabilize the bundles. This approach is extended to post-impact fatigue tensile loadings. Resin damaging is implemented for the shell elements through two fatigue laws Yxy-Nresina and Yxy-Nresinb based on thermodynamical forces and identified through the experimental results obtained in Part I. Fiber breakage is introduced for rod elements through Basquin curves based on tensile and compressive strains. The damage accumulation is taken into account by a Miner’s rule. For several impact energies and amplitude of fatigue loading, the modelling well correlates the experimental results in terms of damage propagation scenario, path and speed.
An explicit finite element modeling of the 5-harness satin woven composite material is proposed in this paper. It is based on the semi-continuous approach. The bundles are modeled with rod elements ...and a specific damageable shell element is used to stabilize this truss structure. As the woven pattern geometry plays a key role in damage initiation and propagation, the rods located at the crimp regions where warp and weft yarns cross each other have been offset to represent the bundles undulations. The main objective of the presented modeling strategy is to represent local bending stiffness variations and damage initiation at the crimp regions without using artificial parameters, but only geometric and material parameters.
The method has been implemented into the explicit finite element code RADIOSS. The modeling strategy is validated by representing a three-point bending test and a drop weight test. It provides good prediction for the local bending stiffness, the impact force history and the damage size and shape. The strain concentration at the crimp regions is well represented.
This article concerns the study of post-impact damage propagation in two thin hybrid woven composite laminates loaded in tension. Low velocity normal drop weight impact tests are first performed. ...Post-impact quasi-static tensile tests are then carried out and monitored by Digital Image Correlation. The influence of the impact energy variation on the fracture surfaces and the residual strength is studied. In order o have a better understanding of the mechanisms involved into the hybrid laminates, four monomaterial sample configurations are also tested. When the damage after impact is barely visible, the sample behaves as a non-impacted sample. When the damage is visible, it propagates whatever the impact energy. The damage grows in the direction perpendicular to the loading for all the monomaterial laminates while two different damage scenarios are observed for the hybrid laminates. The residual strength evolves in three steps depending on the impact energy: first a very low decrease, then an important drop and finally a plateau.
This article concerns the modelling of post-impact damage propagation in thin woven composite laminates. Simulations of low velocity impacts and post-impact quasi-static tension are performed on ...single-material and hybrid laminates. The modelling is based on the semi-continuous approach implemented into the explicit finite element code RADIOSS. The bundles are modelled with rod elements and a specific damageable shell element is used to stabilize this truss structure. Improvements are brought with the introduction of a compressive failure criterion for the rod elements and the development of a pseudo-plastic law with damaging for in in-plane shear. The results provided by the modelling well correlates the experimental observations in terms of damage propagation and load-displacement curves for all the configurations studied.
This paper deals with low velocity and medium velocity impacts on thin carbon/epoxy hybrid laminates made of unidirectional plies and woven fabric layers. Drop weight and gas gun impact tests were ...performed to compare the damage mechanisms of thin hybrid laminates with those of woven laminates of equivalent stiffness and mass. The results show that hybrid laminates present a better impact behaviour in terms of post impact damage extent. These tests were then modeled using a semi-continuous approach. The numerical results well correlate the experiments.
This article deals with the development of a new intralaminar interface in order to extend the semi-continuous strategy already developed by the authors for impacts on thin composite laminates to ...thicker ones. Based on medium experimental observations scale, the new interface introduced aims at capturing transverse resin cracks occurring between fibre bundles of a unidirectional ply. The new element is implemented in the commercial finite element software Radioss®. Results of impact simulations performed on thick HTA7-913 plates (various thicknesses) are compared with experimental ones, and show good agreements in terms of both damage sizes and load-displacement curves.
This article concerns the Finite Element modeling of impacts on composite sandwich structures. Low velocity normal impacts and medium velocity oblique impacts on sandwich panels made with woven ...composite skins and a polyurethane foam core are investigated. The ply orientations and materials of the woven composite laminate skin are varied. The woven skin is modeled using a semi-continuous approach, described in the first part of this two parts article, in which the behavior of the bundles of fibers and that of the resin are disconnected. The foam core is represented with solid elements with a continuous material law. This modeling strategy provides results accurate enough to represent the damage scenario observed experimentally with an acceptable calculation time. The numerical results are used to analyze the damage mechanisms leading to the final fracture shape.
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