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The primary aim of this PhD programme was to understand the fatigue behaviour of magnetorheological elastomers (MREs) and provide a reliable fatigue life predictor for this class of materials. To realise this aim required the study of the dynamic behaviour of MREs using the equi-biaxial bubble inflation test method. Isotropic and anisotropic MREs were fabricated from silicone rubber (SR) filled with soft carbonyl iron (CI) particles. The equi-biaxial fatigue behaviour of these samples was determined using a bubble inflation method. Wohler (S-N) curves for both isotropic and anisotropic MREs were produced by subjecting the compounds to cycling over a range of stress amplitodes (u.). Changes in physical properties, including variation in stress-stretch ratio relations, complex modulus (E*), dynamic stored energy (Wn) and damping loss factor (r/) during the fatigue process, were analysed. In cyclic testing, a limiting value of E* was reached at which fatigue failure occurred in SR based MREs and this supports previous findings for non-strain crystallising rubbers (ethylene propylene diene monomer (EPDM) and styrene-butadiene rubber (SBR)) subjected to uniaxial and equi biaxial loading. It was also substantiated that the dynamic stored energy criterion can be used as a predictor in determining the fatigue life of MREs irrespective of loading levels, the carbonyl iron content, the directionality of the particles and whether or not an external magnetic field was applied.
Interfacial layers play an important role in improving the fatigue resistance of MRE compounds by offering a sensible transition in physical properties between the matrix elastomer and the ferromagnetic particles. An initial attempt to modify the surface of carbonyl iron particles by using a sol-gel method was introduced in this research. Characterisation of MREs with coated particles suggested that the dispersion of particles in silicone rubber was greatly improved after polysiloxane encapsulation.
Consequently, the next phase of the research programme will focus on the design of interfacial layers using the sol-gel method. The coated particles will be used in the fabrication of MREs and the equi-biaxial fatigue behaviour of these samples will be studied to determine the effect of variations in interfacial layers on the fatigue resistance of the composites.
Zhou, Y. (2016) Fatigue Properties of Magnetorheological Elastomers and the Design of Interfacial Layers to Improve Fatigue Life. Doctoral thesis, DIT, 2016.