Fatigue damage mechanism and self-heating effect of polyurethane elastomers under conditions of ambient temperature and loading frequency

Polyurethane (PU) elastomers are widely used in high-stress cyclic load-bearing structures such as subgrade reinforcement and wind turbine foundations. Temperature and loading frequency play critical roles in this process, but the related mechanisms are still poorly understood. Herein, the quasi-static compression and dynamic compression fatigue behaviors of PU elastomers under different temperatures and loading frequencies were investigated, along with SEM observations and real-time temperature monitoring. The results show that the quasi-static compressive strength, elastic modulus, softening stress, and strain energy density decrease with increasing temperature, especially at higher strain rates. The fatigue damage exhibits three stages: adjustment, viscoelastic development, and failure (or cyclic hardening). Higher temperatures accelerate damage evolution and reduce fatigue life; at 0.25 Hz, the fatigue threshold decreases from 1.0 (54.50 MPa) at 0 ℃ to 0.5 (18.94 MPa) at 25 ℃, whereas lower temperatures cause brittle fracture and extend longevity. Higher loading frequencies increase unit-time cyclic deformation, aggravate self-heating and accelerate damage accumulation, with the fastest fatigue evolution and most severe failure observed at 0.5 Hz. The internal temperature of failed specimens exceeds the glass transition temperature (52.59℃) of hard segments, indicating a dominant thermal failure. These findings provide guidance for the application of PU elastomers in load-bearing structures under varying environmental and loading conditions.