Study of low velocity impact damage in CFRP laminates using 3D computed tomography

In this work low velocity impact damage in IM7/977-3 carbon fiber reinforced polymer (CFRP) composites has been investigated using 3D computed tomography (CT). 32-ply IM7/977-3 symmetric cross-ply composites were impacted at different impact energy levels and with different impactors (flat-ended cylindrical and hemispherical) using an Instron 8200 Dynatup drop-weight impact machine. Impact energy was chosen to produce slight damage, which was characterized by the small crack on the front, impacted side and small visible delamination on the back, nonimpacted side of the specimens, and barely visible damage, which was characterized by slight indentation on the impacted side, but no visible delamination on the back side of the specimens. The difference in the impact energy to produce these types of damage was about 30%. Internal impact damage was assessed using ZEISS METROTOM 1500 CT scanning system. CT images were reconstructed using VGStudio MAX. To determine the extent of the damage zone, impacted 6 in by 6 in composite specimens were scanned first. As the relatively large specimen size did not allow for detailed evaluation of damage (internal cracks and delaminations were not visible), smaller 45 mm by 45 mm specimens, with enclosed impact damage zones, were cut out and analyzed. The CT imaging results showed that volume of the impact damage zone had a positive correlation with impact energy, maximum load and maximum deflection, but that relationship was generally weak. Absence of noticeable correlation between damage volume and impact energy was unexpected as the difference in the impact energy was up to 30%.