Purpose: The self-heating effect caused by viscous energy dissipation in polymer-based composite structures subjected to harmonic loads is considered to have a great influence on the residual life of the component. The purpose of the conducted investigations is the determination of the dynamic mechanical behaviour of a polymer-based composite material under different excitation frequencies and temperatures.Design/methodology/approach: The dynamic mechanical analysis was employed for measurements of temperature and frequency dependence of the complex rigidity parameters. Obtained loss rigidity curves for different load frequencies enable the determination of the glass-transition temperatures and finally frequency-dependence of the loss rigidity determined on the basis of the kinetic molecular theory and Williams-Landel-Ferry (WLF) hypothesis.Findings: The dependency between glass-transition temperature and excitation frequency has been investigated. The activation energy of the phase transition as well as the temperature dependence of the shift factor was calculated. The glass-transition temperature and constants of WLF equation enable the determination of temperature and frequency dependence of the loss rigidity according to the time-temperature superposition principle.Research limitations/implications: The ranges of temperatures were limited to 30-150 °C and excitation frequencies to 1-200 Hz, the behaviour of the composite material outside these ranges can be estimated based on the theoretical assumptions only. Obtained dependencies are correct only for linearly viscoelastic materials.Practical implications: Obtained dependencies can be useful for estimation of the mechanical and thermal degradation of polymer-based composites and can be subsequently applied for the determination of fatigue, crack growth and residual life of composite structures.Originality/value: The determination of temperature and frequency dependence of the loss rigidity gives an opportunity to obtain the self-heating temperature distribution of the polymer-based composite structures under harmonic loading.