Experimental and analytical investigation of thermo-mechanical responses of pure epoxy and carbon/Kevlar/S-glass/E-glass/epoxy interply hybrid laminated composites for aerospace applications

Abstract

Most of the aircraft and ship structural components are exposed to different environmental conditions (different temperatures) in various places. Furthermore, helicopter main and tail rotor blades are subjected to turbulence at various frequencies during heavy winds and bird strikes on it. To overcome this, conventional metal components and propeller blades need to be replaced with light weight, advanced hybrid composite materials and also frequency characterization studies are required at different temperatures. Therefore, in this study, the viscoelastic behavior of pure epoxy, E-glass/epoxy and three different hybrid composites (S-glass-E-glass/epoxy, carbon-E-glass/epoxy and Kevlar-E-glass/epoxy) are characterized using dynamic mechanical analyzer (DMA) over the temperature range of 30–150 °C at four different frequencies (1, 10, 50 and 100 Hz). The experimentally obtained storage modulus and loss tangent (tan δ) values are theoretically validated. The least square regression lines are used to obtain the activation energy. The results indicate that the carbon-E-glass/epoxy composites exhibit the highest storage and loss moduli due to stiffening effect whereas pure epoxy exhibits the least storage modulus and highest tan δ peak at all frequencies, as the temperature changes from 30 to 150 °C when compared with other combinations. The glass transition temperature (Tg) increases with the increase in frequency. The sharp decrease in storage and loss moduli are observed in the glass transition zone, which can be attributed to the enhanced mobility of polymer chains owing to matrix softening. Using scanning electron microscopy, the higher debonding regions are seen in tested samples of Kevlar-E-glass/epoxy hybrid composites at higher frequencies.