Evaluation of the strain rate dependent behavior of a CFRP using two different Hopkinson bars

In many studies the strain rate sensitivity of a CFRP material is investigated thoroughly in only one layup and loading direction, which brings about challenges in the comparison of the results due to the large layup- and loading mode-dependence of the material behavior. To address this challenge, in this study we characterize one CFRP material comprehensively in different rate dependent configurations. We demonstrate the feasibility of the Hopkinson Bar technique in the high strain rate testing of CFRP materials. We also highlight the importance of carefully designing and analyzing the experiments for each layup separately. That is, we show how notably different material behavior and therefore notably different test requirements are obtained for the nominally same composite material by simply changing the layup. Two different Hopkinson Bar Set-ups were used; a Direct Impact Hopkinson Pressure Bar (DIHPB) for the characterization of the compressive response of the UD material perpendicular to the fiber direction and a Split Hopkinson Tension Bar (SHTB) for the characterization of the tensile response of three different layups: UD material perpendicular to the fiber direction, a ±45-laminate, and a quasi-isotropic layup. For each studied layup, the specimen geometry, mounting concept and testing approach were individually adapted. As a result, it was possible to comprehensively evaluate the high rate response of the CFRP composite at a strain rate of 200 s^-1 with a high quality of results.