Acoustic Emission based Methodology to Evaluate the Fracture Toughness in carbon/epoxy composites

Fiber-Reinforced Polymer (FRP) composites are an important category of advanced engineering materials. These materials are widely used in the industry due to their unique characteristics such as high specific strength and stiffness. In FRP composite materials, there are several failure mechanisms such as matrix cracking, fiber breakage, fiber/matrix debonding and delamination. Delamination is the most striking one. In this paper, mechanical and acoustic emission (AE) behaviors of delamination are investigated under the actual operation loading modes (i.e. mode I, mode II and the combination of these pure modes). The composite laminates have been fabricated with 14 layers of woven carbon/epoxy prepregs. DCB, ENF and MMB specimens were prepared according to ASTM D5528 and D6671 standards and subjected to the different loading modes. First, inter-laminar fracture toughness of the specimens is calculated using the represented methods in ASTM D5528 and ASTM D6671 standards. Then, fracture toughness of the specimens is determined using the AE-based methods. The results indicate that, the AE-based methods have good applicability to determine the fracture toughness of the composite materials.