15.3.2 Weft Tensile Tests Tensile tests on the dynamic weft specimens were realized with servo-hydraulic machine from quasi-static to dynamic strain rates. 3 tensile tests per speed were ran for 1:7 10 3 ms 1, 0.01 ms 1 and 1 ms 1. Weft elastic moduli, normalized by quasi-static warp elastic modulus, are described in Fig. 15.5a. As shown in warp case, dispersion in weft elastic modulus is negligible. Weft elastic modulus strain rate sensitivity is not significant between 10 4 and 10 s 1. Poisson’ ratio also evaluated by DIC allows to make the same observation. In warp and weft directions, 3D carbon/epoxy woven composite mechanical behaviour under εl <0:4 %can be considered linear elastic. 15.4 Conclusions Quasi-static warp and weft 3D carbon/epoxy woven composite tensile specimens require to apply load levels that could not be reached with dynamic servo-hydraulic testing machine. Specific dynamic specimens were then developed in order to adapt the specimens strength to the dynamic testing machine capacity. Reference tensile specimens geometry are one Unit Cell width. Dimensional and positional sensitivities of the elastic modulus characterization were studied by Finite Element tensile test simulations. In warp and weft cases it was observed that the elastic modulus quantification could be properly performed by reducing the reference width (W) and length (L). Elastic modulus obtained in both cases, with a 0.75 Unit cell width (L ¼1 in warp direction and L ¼1.5 in weft direction) is less than 1.5 % different from the reference, and relatively independent of the virtual specimen position. A length reduction specimen permits to reach upper strain rate levels than the reference one. Elastic modulus obtained with the quasi-static and the dynamic tensile specimens at 10 4 s 1 prove a good correlation with respect to the virtual testing approach. From specific dynamic warp and weft tensile specimens, quasi-static to dynamic tests were run in order to characterize the stain rate sensitivity of the 3D carbon/epoxy woven composite linear mechanical behaviour. Elastic modulus and the Poisson’ ratio obtained in both cases show a independence to the strain rate between 10 4 and 10 s 1. In conclusion, warp and weft mechanical behaviour under εl <0:4 %of the 3D carbon/epoxy woven composite can be considered linear elastic. Acknowledgements This research was supported by SAFRAN Snecma. We thank our collegues from SAFRAN (Y. WIELHORSKI, T. FIXY, . . .), ONERA (M. RAGONET, A. DEUDON, . . .), Centrale Lille and LML who provided expertise and technical support that greatly assisted the research. We thank E. Deletombe (ONERA) for assistance with particular scientific methodology and for comments that greatly improved the manuscript. 10−4 10−3 10−2 10−1 100 101 102 10−4 10−3 10−2 10−1 100 101 102 0 0.2 0.4 0.6 0.8 1 Strain rate (s−1) Strain rate (s−1) Normalized elastic modulus 0 0.2 0.4 0.6 0.8 1 1.2 Normalized Poisson’ ratio ν21 a b Fig. 15.5 Dynamic weft tensile tests. (a) Weft elastic modulus. (b) Poisson’ ratio ν21 15 Characterization of High Strain Rate Dependency of 3D CFRP Materials 115
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