Characterization of High Strain Rate Dependency of 3D CFRP Materials
New composite materials are increasingly used in aviation to reduce the mass of structures. Aeronautic structures have to be designed with respect to a broad range of mechanical loadings during their operational life. These loadings are considered in the
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Characterization of High Strain Rate Dependency of 3D CFRP Materials N. Tran, J. Berthe, M. Brieu, G. Portemont, and J. Schneider
Abstract New composite materials are increasingly used in aviation to reduce the mass of structures. Aeronautic structures have to be designed with respect to a broad range of mechanical loadings during their operational life. These loadings are considered in the design by numerous cases, from low up to high speeds. The motivation of the presented work is to establish and characterize the high strain rate dependency of the linear behavior of composites materials. More specifically, new generations of 3D carbon/epoxy composite materials are of interest because of their high mechanical performances, which require specific experimental developments to be done. Due to the large size of their textile Unit Cell and carbon fiber high strength and stiffness, unusual dynamic test capabilities are required, which leads to revisit the test protocols, specimens definition, instrumentation and exploitation techniques. The experimental method described in this work is applied to analyze the strain rate sensitivity of the mechanical behavior of such a 3D woven composite material. The experiments are done with a servo-hydraulic testing machine (ONERA) in a strain rates range varying between 104 and 10 s1. The linear mechanical behavior of the material in the warp, weft and 45∘ orientations is characterized. These tests, together with the new experimental protocol, permit to accurately reveal and measure the material behavior strain rate sensitivity, which proved to be large in the 45∘ direction. Keywords Composite • 3D woven • Strain rate • Experimental • Characterization
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Introduction
Currently, different woven composite material configurations exist. Woven architecture can be made in different textile types (taffeta, twill, 3D, 4D, 5D, . . .). This study focuses on an epoxy reinforced by layer/layer unbalanced carbon fibers woven developed by SAFRAN Snecma. This Unit Cell, described in Fig. 15.1, as a significant size compared to classic 2D woven composites. The composite volumic warp/weft fibers ratio studied is low unbalanced. This composite is made of two weaving directions, called warp (blue) and weft (red). Warp yarns weaving with different layers interlocks each layer together. This woven composite particularity prevents the fragile delamination phenomenon to appear. As Schneider [1] shows in quasi-static tensile tests (_ε ’ 104 s1), 3D carbon/epoxy woven composite mechanical behaviour is orthotropic. This woven composite mechanical behaviour presents two domains, firstly a linear one in which the damage is negligible at the macroscopic scale. The second one is a non linear domain due to the development of damage (matrix cracks, fiber yarn cracks, decohesion fiber yarn/matrix). The in-plane mechanical behaviour of this specific 3D woven composite has been mainly studied under quasi-static or fatigue loadings [1, 2, 3, 4]. In structure lifecycle, particulary for aeronautic application
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