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The equi-biaxial fatigue behaviour of silicone based magnetorheological elastomers (MREs) with various volume fractions of carbonyl iron particles ranging between 15% and 35% was studied. Wöhler curves for each material were derived by cycling test samples to failure over a range of stress amplitudes. Changes in complex modulus ( E ∗ ) and dynamic stored energy during the fatigue process were observed. As for other elastic solids, fatigue resistance of MREs with different particle contents was shown to be dependent on the stress amplitudes applied. MREs with low particle content showed the highest fatigue life at high stress amplitudes while MREs with high particle content exhibited the highest fatigue resistance at low stress amplitudes. E ∗ fell with the accumulation of cycles for each material, but the change was dependent on the particle content and stress amplitude applied. However, each material failed in a range suggesting a limiting value of E ∗ for the material between 1.22 MPa and 1.38 MPa regardless of the particle content and the magnitude of the stress amplitude. In keeping with results from previous testing, it was shown that dynamic stored energy can be used to predict the fatigue life of MREs having a wide variation in particle content. [ABSTRACT FROM AUTHOR]

Abstract: For materials in modern machines, fatigue strength is probably the most critical physical property that needs to be understood. In particular, the high dynamic loading experienced by machine parts necessitates understanding fatigue properties in life limiting components. However, rubber fatigue is imperfectly understood and even less is known about fatigue resistance in adaptive or smart elastomers. Preliminary research into the equi-biaxial fatigue behaviour of magnetorheological elastomers (MREs) is described here. Test samples were fabricated by incorporating carbonyl iron particles, typically of 6–7μm in diameter, in room temperature vulcanised (RTV) silicone rubber. Physical testing was conducted using a bubble inflation testing system and test samples were fatigued at stress amplitudes between 0.75MPa and 1.4MPa under engineering stress control. S–N (Wöhler) curves of stress amplitude (σ a = S) versus cycles to failure (N) are presented. Stress–strain behaviour throughout the fatigue process is also described. For a stress amplitude of 0.75MPa and zero minimum stress, stress softening was observed for the entire test, though it was particularly pronounced in the first 100 cycles of testing. A limiting value of complex modulus (E* ), observed previously in dynamic testing of conventional elastomers, was determined in these tests. [Copyright &y& Elsevier]

In this work, polyphenolic extract from walnut green husks (denoted as walnut polyphenols), which is an abundant agroindustrial residue/waste, was used to modify barium titanate (BT) particles in the preparation of silicone rubber (SR) based dielectric elastomer (DE) composites with enhanced electromechanical performance. By employing walnut polyphenols modification, the dispersibility of BT particles in the SR matrix and the compatibility between BT and SR were greatly improved, which resulted in enhanced mechanical performance of the DE composites. Dielectric property measurement showed that DE composites containing walnut polyphenols modified BT particles (WNBT) had higher dielectric constants and lower dielectric losses than that of DEs with unmodified BT particles. Furthermore, it was found that the walnut polyphenols modification resulted in decreased dielectric loss tangent of the DE composites, suggesting an improved compatibility between the modified BT particles and SR. Finally, the static and dynamic electromechanical performance of the DE composites were evaluated. The SR/5% WNBT composite achieved the highest actuated area strain of 38% among the SR based composites used in this work. Moreover, the actuated area strain of SR/WNBT composites exhibited excellent electromechanical stability during the application of cyclic voltage signals. Unlabelled Image • Walnut polyphenols extracted from walnut husks were used to modify barium titanate (BT) particles. • The dispersibility of BT in silicone rubber (SR) and the compatibility between BT and SR was improved after modification. • The SR/WNBT composites achieved the highest actuated area strain of 38%. • The actuated area strain of SR/WNBT composites exhibited excellent stability during 50 cyclic voltage signals. [ABSTRACT FROM AUTHOR]