Strain and Damage Assessment of Treated and Untreated Luffa Mat Composite Using Acoustic Emission and Digital Image Correlation

In this work, acoustic emission and digital image correlation were applied to three different composites reinforced with treated (2% and 5% NaOH) and untreated luffa fibers during tensile testing, to follow the evolution of the different damage modes and determine strains and Poisson’s ratio. The tensile test results showed that alkaline treatment of 5% improved Young’s modulus and tensile strength. In comparison, the 2% treatment showed the most outstanding improvements in mechanical properties. The K-means clustering methodology identified four types of damage: matrix cracking, fiber pull-out, delamination, and fiber breaking. The 5% treated composite had lower cumulative energy and hits than the untreated and 2% treated composites, implying that the T5% composite suffered less damage. The DIC results showed that the longitudinal strains found by the extensometer are very approximate to those found by DIC, this technique also allows us to find the transverse strains of the composites UT (0.324), T2% (0.295), and T5% (0.207%). It is shown that the 5% alkaline treatment leads to the decrease of Poisson’s ratio (0.2378) compared to 2% treated (0.3113) and untreated (0.3120) composites. Based on AE, DIC results, and mechanical properties, the T5% composite is the most successful.