Experimental investigation on the response of unidirectional flax fiber composites to low-velocity impact with after-impact tensile and compressive strength measurement

This study investigated the low-velocity impact tolerance of flax fiber/epoxy composite reinforced by unidirectional fibers. Visual inspection and ultrasonic scanning were employed to assess the external and internal damage under impact, and to investigate their dependencies to the impactor shape as well as the impact energy. The results show that impacted specimens experience various types of fracture, matrix cracking, fiber breakage and delamination, where the impact shape shows a clear effect on the damage extent. Tensile tests show a significant effect of the residual damage, which decreases the residual strength by 41% at 5J. The impact-induced damage did not affect significantly the compressive behavior for an impact energy less than 3J. Depending on the damage extent, high impact energy shows a significant strength reduction. The effect of pre-existing damage under compressive load, monitored by the DIC system, has shown a substantial effect on the buckling mode and both residual cracks and delamination development.