Relief of Cure Stress in Prepreg Composites with Engineered Voids: A Solution to Warping in Composite Phenolic Resin/Fiberglass Laminates

Abstract

The warp of a phenolic resin/fiberglass honeycomb composite panel is investigated using void and volatile analysis, and a solution to geometric warp is proposed and tested. The surface void content in semicured phenolic polymer composite facesheets was found to be an indicator for the average warp value of a fully cured composite laminate panel. Several potential sources in the resin formulation for producing voids in the phenolic resin/fiberglass composite sheets were investigated. Ultimately, high surface tension and polymer incompatible cosolvents are correlated to the population of voids. It is proposed that these voids act as sites for the relief of internal stresses that develop in the phenolic matrix during the final cure of the part. Void-inducing additives are added at the formulation stage which phase separate from the polymer matrix in partially cured fiberglass/phenolic composite sheets, and upon evaporation, lead to voids that prevent warping in honeycomb composite panels.

Synthesis and Characterization of Tunable, pH-Responsive Nanoparticle–Microgel Composites for Surface-Enhanced Raman Scattering Detection

“…A TA Instruments Q500 TGA instrument equipped with an inline Thermo Scientific iS10 FTIR gas cell spectrometer was used for both the TGA and TGA−FTIR experiments. 96 To monitor the mass changes during thermal degradation and to determine the NP-loading, TGA experiments were conducted with a 15 min isotherm at 100 °C followed by a 20 °C/min ramp from 100 to 800 °C. An isotherm before and after this temperature program was held for 5 min to monitor the background signal of FTIR spectra.…”

Pegylated Polybenzoxazine Networks with Increased Thermal Stability from Miscible Blends of Tosylated Poly(ethylene glycol) and a Benzoxazine Monomer

“…A TA Instruments Q500 thermogravimetric analysis (TGA) instrument equipped with an inline Thermo Scientific iS10 Fourier transform infrared (FTIR) gas cell spectrometer was used for TGA/TGA-FTIR experiments. 48 TGA experiments were preformed with a 1 min isotherm at 75 °C followed by a 25 °C/min ramp from 75 to 30 °C and then a 10 °C/min ramp from 30 °C to a minimum of 400 °C to analyze the weight changes during the melting and curing of BA-a, mPEGOH, mPEGOTs, and their blends and to determine any char yields. An isothermal transfer line (225 °C) was used to direct effluent from the TGA sample furnace to the FTIR spectrometer using dry nitrogen as a carrier gas (flow rate = 90 mL/ min).…”