Multiscale Characterization of E-Glass/Epoxy Composite Exposed to Extreme Environmental Conditions

Fiber-reinforced polymer matrix composites continue to attract scientific and industrial interest since they offer superior strength-, stiffness-, and toughness-to-weight ratios. The research herein characterizes two sets of E-Glass/Epoxy composite skins: stressed and unstressed. The stressed samples were previously installed in an underground power distribution vault and were exposed to fire while the unstressed composite skins were newly fabricated and never-deployed samples. The mechanical, morphological, and elemental composition of the samples were methodically studied using a dynamic mechanical analyzer, a scanning electron microscope (SEM), and an x-ray diffractometer, respectively. Sandwich composite panels consisting of E-glass/Epoxy skin and balsa wood core were originally received, and the balsa wood was removed before any further investigations. Skin-only specimens with dimensions of ~12.5 mm wide, ~70 mm long, and ~6 mm thick were tested in a Dynamic Mechanical Analyzer in a dual-cantilever beam configuration at 5 Hz and 10 Hz from room temperature to 210 °C. Micrographic analysis using the SEM indicated a slight change in morphology due to the fire event but confirmed the effectiveness of the fire-retardant agents in quickly suppressing the fire. Accompanying Fourier transform infrared and energy dispersive X-ray spectroscopy studies corroborated the mechanical and morphological results. Finally, X-ray diffraction showed that the fire event consumed the surface level fire-retardant and the structural attributes of the E-Glass/Epoxy remained mainly intact. The results suggest the panels can continue field deployment, even after short fire incident.

Parametric instability analysis of sandwich plates with composite skins and LPRE based viscoelastic core

In the present analysis, the parametric instability regions of a three-layered sandwich plate with thin composite skins and leptadenia pyrotechnica rheological elastomer (LPRE) core under axial periodic compressive load is studied for five different boundary conditions. The governing equation of motion is derived using finite element method (FEM) which is in the form of a parametrically excited system. The instability regions of the sandwich plate are found using modified Hsu method. The shear storage modulus and loss modulus of the newly developed LPRE core is determined experimentally and used in this analysis. The dynamic properties of the LPRE based sandwich plates are observed to be better than those of the room temperature vulcanised elastomer core based sandwich plates. The critical dynamic loads and the corresponding frequencies are found which will find various applications in structural design.