Scale effects on the response of composite structures under impact loading

Abstract

Science Arts & Métiers (SAM)is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. AbstractFor several years, composite materials have taken a significant part in the realization of structures designed for transport (aeronautical, nautical, automotive...). In order to qualify the behavior of such structures, preliminary validation tests have to be done. These specific tests are often very expensive and difficult to set up, especially when the structure dimensions are large (fuselages of aircraft, ship hulls...). An alternative way is then to employ small-scale models.The use of these reduced scale structures requires the identification of similitude models allowing the extrapolation of the small-scale model behavior to the real structure. Although largely developed in the case of homogeneous materials, such similitude techniques are not clearly identified for composite materials taking into account the damage evolution during an impact.The purpose of this article is firstly to present existing similitude techniques making it possible to predict the composite structure behaviour from the knowledge of small-scale model response. Secondly, experiments were done on two scale of samples carried out by stratification of unidirectional carbon/epoxy plies. These results were finally compared with the analytical predictions of similitude laws currently used.The aim of this paper is to contribute to similitude laws development applied to composite structures. These laws permit to extrapolate the small-scale model behavior to the real scale one. Existing approaches have been established following two different methods. They are summarized in this paper and applied to impact loadings on two laminated plate scales. In order to complete data collected by ''conventional'' instrumentation (force transducer, displacement sensor, accelerometer.. .), optical device such as an high-velocity CCD camera, associated with optical techniques for the monitoring of markers, were used. These techniques make possible to compare displacement lines corresponding to each scale. It is shown that existing similitude laws, used for elastic materials, do not allow to simulate the behavior of the real scale when this one is damaged.

On the Prediction of the Residual Behaviour of Impacted Composite Curved Panels

“…Obviously, the damage generates decreasing stiffness. This phenomenon has been observed experimentally (Ballère et al, 2008) and could be analyzed in detail using this approach. Nevertheless, because the aim of this study is to predict the residual tensile strength of impacted specimens, particular attention was paid to the ultimate stress.…”

“…This observation was undertaken during the experimental study (Ballère et al, 2008) and the results are summarized below. For the impact tests, the specimen was clamped between two aluminium blocks and tightened with screws.…”

“…As an experimental study of damage tolerance using this type of structure is very expensive, the experiments were performed on curved panels extracted from tubes which had the same geometrical and mechanical properties as the vessels. The experimental procedure was carried out on these curved panels and the whole of the results were presented in a previous paper (Ballère et al, 2008): Firstly, the specimens were impacted to simulate an accident which can occur on such structures. Then, they were loaded in tension, according to their longitudinal axes, to reproduce the axial stresses caused by internal pressure being applied to the vessels' bottoms.…”

“…The methodology used and the results obtained for one of these scales of specimens (called «specimens Ø600») is presented in (Ballère et al, 2008). The first step in the numerical modelling is to check that the behaviour of an undamaged specimen is well-predicted.…”

“…From these similitude models, some authors (Morton, 1988, Nettles et al, 1999 studied scale effects on composite structures taking into account the damage evolution during an impact but the gap was important between experimental results and predictions issued from scale models. For our study, in a preliminary phase of this research, scale models were evaluated (Viot et al, 2008) : a first approach consisted to apply similitude laws currently used on two scales (A and B) of composite structures . The purpose of this preliminary study was to predict the behaviour of the composite structure (scale A) from the knowledge of the response of the second scale model (scale B).…”