Evaluating microstructural variation in nanocomposites via thermoelastic stress analysis

Abstract

This work reports distinct thermo-elastic behavior during the monotonic tensile loading of epoxy-based polymer matrix nanocomposites comprised of varying weight fractions (wt.%) of amine-functionalized multi-walled carbon nanotubes (MWCNT) and amine-functionalized graphene nanoplatelets (GNP). Four configurations—0.1 wt.% and 0.2 wt.% of CNT/epoxy and GNP/epoxy—were produced for this study. With the addition of nanofillers, an improvement in tensile strength of 36.00 ± 1.85% was achieved in 0.2 wt.% CNT/epoxy samples and 30.00 ± 4.08% in 0.1 wt.% GNP/epoxy compared to the baseline epoxy. Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were conducted to determine glass transition temperature (T _g ), specific heat capacity (C _p ), and coefficient of thermal expansion (CTE) of baseline epoxy and the nanocomposites. Temperature profiles were measured during monotonic tests of nanocomposites using an infrared thermography (IRT) camera, yielding distinctive temperature-stress profiles based on thermoelastic stress analysis (TSA). The initial slopes of these temperature-stress plots, known as the thermoelastic constant (K₀), were determined graphically for all the nanocomposite specimens. K₀, thus obtained from monotonic testing, was in the same range of the values obtained from equivalent DSC/TMA measured values for the chosen nanocomposites in this study. Thus, K₀ measurements from TSA can be used as a novel way to discern a nanocomposite’s microstructural composition.