Characterization of interfacial integrity and its implication on mechanical behavior of FRP composites

Abstract

Fiber reinforced composites (FRP) have been gaining much attention recently because of their use in load carrying parts of new aircraft such as Boeing 787and in non-aerospace applications such as in ships, in retrofitting of structurally deficient bridges, and transportation. Besides this, composite structures in service are typically subjected to different environmental conditions, which may affect their mechanical performance as well as their flammability potential. Water that diffuses in to the composite ends up either in the matrix or at the interphase region. In the matrix, water would act as a plasticizer, increasing the free volume, lowering the glass transition temperature (Tg), and relieving the internal stresses that was built up during processing of the composite. In many cases failures occurs in the interface region due to chemical reactions/plasticizing when impurities (commonly water) penetrate the interface. The continuous change in interfacial chemistry and character under the influence of various environment often leads to a micro changes such as increase of internal voids of the entangling polymer chain, fiber/matrix interfacial bond failure and microcrack formation in to the matrix.

Recently an active area of investigation related to this work is being explored by Temperature Modulated differential scanning calorimetry (TMDSC) and Fourier Transform Infrared Spectroscopy(FTIR-Imaging) ,Ultraviolet spectroscopy (UV),techniques to pin down the causes for a reduce stress transmissibility at the interface. Surface treated glass fiber, carbon fiber and epoxy matrix were used to fabricate micro-composite. Change in FTIR spectra shows alternation and deviation of stoichiometry.The analysis of these suggests that there is a variation in the chemical structure of the matrix from the fiber to the polymer bulk due to different conversions arising from a gradient in the initial composition. And in TMDSC the focus has been emphasized on Tg value which increases when hygrothermal treatment duration is less because of formation of double hydrogen bond and replacing the covalent bond. The increase in Tg value may often lead to the enhanced mechanical properties like interlaminar shear strength and fatigue strength.