•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 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 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.
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.
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.
In this work, the influence of a tensile preload on the impact behavior of thin woven composite laminates is investigated. These kinds of laminates are usually parts of more complex structures, for ...example, skins of structural sandwich panels or helicopter blades. These structures are generally subjected to external loads, and can also be impacted in operation. The objective of this study is to identify a correspondence between the preload of the structure and the resulting impact damage. This preliminary work is a first step of a more global study that aims at predicting impact damage in structural composites in order to optimize the design process. Experimental tests are carried out on carbon/epoxy and glass/epoxy mixed thin laminates and on sandwich structures. The samples are loaded uniaxially using a specially designed test rig. The effect of the preload on the impact damage size and shape and the peak load is experimentally quantified and discussed.
The paper is devoted to the incorporation of radionuclides by pregnant or nursing women, as a consequence of both environmental contamination and diagnostic administration of radiopharmaceuticals, ...and the transfer of these radionuclides from the mother's body to the embryo or foetus and from the mother's diet to her milk. International knowledge on these issues is reviewed. Furthermore, some calculations carried out by the authors, estimating the activity of some typical radionuclides and the depleted uranium needed to expose the embryo/foetus to a 1-mSv equivalent dose, are reported.
The radiological impact of Chernobyl accident on the Italian population has been reassessed on the basis of the activity average values, measured in environmental and food matrices since 1986. The ...evaluation has been made taking into account the new risk estimates by the International Commission on Radiological Protection (ICRP). Moreover, in order to compare the calculated doses with data from Whole Body Counter and to check models describing the time trend of radioactive contamination, the activity levels systematically measured in the Emilia Romagna district (Northern Italy) were considered. The dose assessment has been compared with the European one made by UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation).
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