Post-impact Fatigue of a composite reinforcement woven of hemp fiber and epoxy matrix

The purpose of this work is to study the resistance to low velocity impact of woven hemp/epoxy composite and the influence of impact damage on its residual strength in tensile and fatigue loading. The composite consists of 7 plies of woven hemp fabric and the volume fraction of reinforcement is 35%. A falling dart testing machine was used to perform impact tests at three energy levels: 2.5, 5 and 10 J. Internal damage was characterized by optical microscopy. These observations and the impact tests results were compared to those found in the literature for other composites. Static tensile tests were performed on non- impacted and impacted specimens at each energy level to characterize the influence of the impact on the static tensile behaviour. Other specimens were impacted at 5 J and were tested in fatigue with R = 0.01, at frequency of 1 Hz for three levels of maximum stress: 80%, 60% and 40% of the ultimate tensile stress. The fatigue behaviour was compared to that of non- impacted specimens and damage was monitored by acoustic emission.