Energy dissipation of stitched and unstitched woven composite materials during dynamic compression test

Split Hopkinson Pressure Bar is one of the main methods used to characterize the dynamic behaviour of composite materials. In this study, we performed several impact tests for unstitched (2DWC) and stitched (3DWC) woven composites in order to obtain a reliable comparison between dynamic properties of these materials. On the other hand, an energetic study was carried out during these tests to draw up the energy balance and to quantify the energy dissipation. The impact energy is the kinetic energy of the striker bar and it is the total energy quantity available at the beginning. At the interface bar/sample, some of this energy is absorbed by the specimens and can cause plastic deformation or damage in a different form, which can lead to heat generation. The remaining energy corresponds to the reflected and transmitted energy and can be determined from the measured deformation profile. The test results shows that stitch reinforcement can increase resistance in comparison with the standard composite. Moreover, the existence of Z-fibres made the fracture more complex and caused several characteristic phenomena, so that the required fracture energy for crack propagation was increased. Stitching does not improve the damage initiation strength but significantly prolongs the duration of the crack propagation phase.