Scale effects on the response of composite structures under impact loading

For several years, composite materials have taken a significant part in the realization of structures designed for transport (acronautical, 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 Lip, especially when file structure dimensions are large (fuselages or 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 arc 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. (c) 2007 Elsevier Ltd. All rights reserved.