Micromechanics of Internal Frictions in Thermoplastic Composites Exposed to High-Frequency Vibrations

Recently introduced class of fiber-reinforced thermoplastic polymer composites (FTPC) in aerospace structures offer a high stiffness-to-weight ratio, cost-saving, and recyclability advantages compared to their thermoset composites. However, their structural performance under high-frequency vibratory loads during their service life is not well understood. Such loads instigate internal material friction inside the microcracks. In this paper, we propose a combined dynamic characterization and fracture mechanics modeling for evaluating the evolution of damage precursors (microcracks) in FTPC due to the presence of internal frictional forces. In order to run simulations to calculate self-heating caused by vibration, one must run transient analysis, because of the contact elements which calculate the amount of friction generated. This work proposes for the first time to apply the structure’s Operating Deflection Shape as a dynamic load to include that friction. An innovation of the proposed method is the inclusion of microscopic self-heating in the microcracks as a consequence of high-frequency frictional forces. The Finite Element Method (FEM) is utilized to perform the dynamic analysis for a thermoplastic composite beam with a microcrack exposed to high-frequency vibration fatigue.