Characterization of low-velocity impact and post-impact damage of luffa mat composite using acoustic emission and digital image correlation

Abstract

In this paper, low-velocity impact and compression after impact damage tolerance of composite reinforced with natural luffa mat were studied for the first time. The effect of impact energy and the influence of the damaged area on the residual mechanical properties under compression were investigated. Acoustic emission (AE), digital image correlation (DIC) and scanning electron microscopy (SEM) were used for the evolution of different damage modes and displacement fields. The findings of the experiments reveal that compression after impact tests of 1, 2, and 3J show a significant effect of the residual damage which decreases residual compressive strength by 12.61, 24.14, and 30.9%, respectively, compared to the unimpacted composite, but Young’s modulus was not significantly affected. Multivariable statistical analysis of the AE signals identified four classes of damage: matrix cracking, fiber-matrix debonding, delamination, and fiber failure. It also showed that the damage mode of unimpacted composites which presents the majority of the amplitude events of the AE signals is mainly due to fiber failure, by contrast, for impacted composites the damage mode is mainly due to fiber-matrix debonding. The AE results are convincing and they were confirmed by SEM images of the fractured faces of the specimens, which revealed the main causes of material failure during the compression after impact test. The DIC system monitored the effect of pre-existing damage under compressive loading and found that increasing impact energy increases the stress concentration around the impacted area and has a significant effect on residual crack development, much more in the loading direction.