Experimental material characterization and mathematical modelling of viscoelastic woven fabric composite shaft for dynamic analysis

This study presents an experimentally validated operator-based viscoelastic modelling framework for the dynamic analysis of woven fabric composite rotor shafts. Woven carbon fabric/epoxy composite specimens (20% fabric volume fraction) were characterised using Dynamic Mechanical Analysis (DMA) over a frequency range of 0–100 Hz at 27°C. A standard four-element linear viscoelastic model was identified as the optimum rheological representation, and its parameters were extracted using a Genetic Algorithm–based curve-fitting procedure with minimal deviation from experimental data. The operator parameters where found to be approximately identical due to the woven architecture along the longitudinal and transverse direction. To avoid excessive computational complexity, the resulting higher-order modulus operator was reduced to an equivalent lower-order form without compromising accuracy. The reduced operator was incorporated into a finite element (FE)–based state-space formulation to investigate the rotor dynamic behaviour of the viscoelastic composite shaft. A detailed parametric study revealed a symmetric stability trend with respect to fibre orientation, where the Stability Limit Speed (SLS) decreased from 3690 rpm at 0° to a minimum of 3190 rpm at 45°, and increased again towards 90°. This behaviour is attributed to stiffness redistribution caused by woven fibre orientation. The results demonstrate the critical role of viscoelastic material modelling and fabric orientation in governing the stability and dynamic response of composite rotor shafts.