Evolution of mechanical properties and magnetorheological effect of polyurethane-based magnetorheological elastomers under longterm cyclic shear loading

Polyurethane-based magnetorheological elastomers (PU-MREs) are promising for for magnetically controlled sealing, vibration reduction, and impact buffering, yet their mechanical evolution and magneto‑responsive retention under long‑term cyclic loading are poorly understood. Effective stiffness, storage modulus, loss modulus, and loss factor were used to characterise stiffness and deformation behaviour and damping and energy-dissipation performance, and a multidimensional evaluation framework comprising fundamental mechanical properties, long-term performance retention, and magnetorheological effects was established.Pure PU and PU-MRE specimens filled with 20 wt% and 30 wt% carbonyl iron powder (CIP) underwent 10 000 zero-magnetic-field shear cycles under 10 % pre-compression, 5 % shear-strain amplitude and 1 Hz loading frequency. Short-duration magnetic-field characterisations at 100 mT and 150 mT were performed at the initial state, after 5 000 cycles and after 10 000 cycles. The long-term mechanical evolution of all three specimens comprised initial adjustment, intermediate stable evolution, and late-stage degradation and structural reorganisation. The 20% CIP specimen exhibited stiffness and energy-storage retention comparable to pure PU, with relatively high damping and energy-dissipation performance, whereas the 30% CIP specimen showed superior dynamic load-bearing capacity, deformation resistance, and elastic energy-storage retention. Long-term cyclic loading attenuated the magnetically induced stiffness responses of both PU-MRE specimens. After 10,000 cycles at 150 mT, the 30% CIP specimen retained a 7.1% relative magnetorheological effect in storage modulus, whereas the loss modulus and loss factor of the 20% CIP specimen increased by 9.6% and 8.3%, respectively. The former therefore retained a favourable magnetically induced elastic response for magnetically controlled sealing and variable-stiffness support, while the latter retained a favourable magnetically induced damping and energy-dissipation response for vibration reduction and impact buffering. This study provides a basis for performance evaluation and parameter selection of PU-MREs under long-term service conditions and methodological guidance for material selection and magnetic-field parameter matching of MREs.