Abstract <p>The aim of the present study is to experimentally investigate the effect of complex loading conditions on deformation behavior, damage accumulation, and fracture mechanisms of fiberglass specimens containing pre-existing cracks. Particular attention is devoted to the influence of preliminary cyclic loading and superimposed torsional vibrations on the kinetics of damage evolution. The experimental methodology involves the application of ultrasonic and thermographic techniques, which enable the detection and characterization of delamination zones under various loading regimes. It has been established that torsional vibrations exert a substantial influence on damage evolution and crack propagation. This effect is of considerable practical significance for assessing the strength and durability of composite structures operating under pronounced vibration conditions.</p>