Damage Detection of CNT/CNC-reinforced Foam-cored Sandwich Composites by Acoustic Emission Tests under Flexural Load

Abstract

Sandwich composites stand out especially in the aerospace industry owing to their high strength-to-weight ratio, one of the most prominent factors for material selection. Polymeric foams as core material in sandwich composites are likely to prevent delamination between face sheets and core by augmenting the contact surface area, resulting from their closed-cell structure. Polymeric foam properties can be enhanced by adding nanomaterials such as carbon nanotubes (CNTs), however increased CNT content or the type of CNTs might arise critical problems such as agglomeration and irregular distribution of nanomaterials. Cellulose nanocrystals (CNCs) are claimed to be good candidates to prevent nanomaterial reinforcing related issues and further, their inclusion enables reinforcing of polymeric foams using an optimum CNT/CNC concentration. In this work, CNT/CNC reinforced polyurethane (PU) foam-cored sandwich composites were manufactured and characterized for the influence of nanomaterial addition on the mechanical properties with an aim to find the optimum nanomaterial content. 0.1 wt.% CNT, CNC, CNT/CNC (1:1), and CNT/CNC (1:2) reinforced PU foam-cored sandwich composites were subjected to simultaneous three-point bending tests and acoustic emission tests, one of the promising non-destructive testing methods enabling insitu monitoring of the damage mechanisms to understand how damage evolves. The effects of these nanomaterial additives on damage mechanisms and the mechanical properties were

Application of Acoustic Emission to Detect Damage in Composites Materials

“…The test results showed that reinforcements can affect the retardation and/or elimination of core damage, face sheet-core debonding, matrix cracking and fiber breakage in Fiber-Reinforced Composites -Recent Advances, New Perspectives and Applications the sandwich composite structures. With the addition of 0.1 wt.% CNT caused the strengthen of core material, as a result, the ratio of AE signals related to fiber breakage and core damage was decreased[77].Kalteremidou et al used AE to identify the dominant stress/strain component in carbon/epoxy composite materials even before damage mechanisms became evident. The result showed that AE can applied for identification of the dominant stress/ strain component at early loading steps[78].…”