Magnetorheological (MR) rubber materials are controllable composites that consist of magnetically polarisable particles in a rubber matrix. They belong to a group of socalled "smart materials" that have seen an increased interest recently. These materials have rheological properties that can be changed continuously, rapidly and reversibly by an applied magnetic field. With suitable control algorithms and solid state electronics, they can respond to changes in their environment. Although few applications of these materials have yet been reported in the literature, the possibilities for materials with controllable stiffness are numerous. Examples of potential applications are tuned vibration absorbers, and stiffness-tuneable mounts and suspensions.The purpose of this work is to increase our knowledge relating to magnetorheological materials for damping applications, using construction rubber as the matrix. The materials should exhibit large responses to an applied magnetic field and have good mechanical properties. In order to simplify their manufacture, the use of a magnetic field during production should, if possible, be avoided.MR rubber materials were made from nitrile and natural rubber, and irregularly shaped iron particles several micrometers in size. The particles were not aligned by a magnetic field prior to the vulcanisation; hence, the materials can be considered to be isotropic. These materials show a large MR effect, e.g. an increase in the shear modulus when a magnetic field is applied, although the particles are not aligned within the material. This is explained by the low critical particle volume concentration (CPVC) of such particles. Similar behaviour can be obtained with materials containing carbonyl iron, if the particles are aggregated and thereby behave like large irregular particles. The iron particle concentration has to be very close to the CPVC in order to obtain a large MR effect.The absolute MR effect in isotropic MR rubber materials with large irregular iron particles is independent of the matrix material, and the relative MR effect can thus be increased by the addition of plasticisers. Other ways of increasing the MR effect are to increase the strength of the magnetic field, although the materials saturate magnetically at high field strengths, or to use small strain amplitudes. The strong strain amplitude dependence of the MR effect suggests that isotropic MR rubber materials are most suitable for low amplitude applications, such as sound and vibration insulation. Measurements at frequencies within the audible frequency range show that this is a promising application for isotropic MR rubber materials.

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The aim of this work has been to ®nd a simple, non-destructive method for determination of the concentration of active antioxidant in HTPByAP composite propellants. Differential Scanning Calorimetry (DSC) was used for determination of Oxidation Induction Time (isothermal OIT) and Oxidation Induction Temperature (dynamic OIT) at different antioxidant concentrations. The ammonium perchlorate content in the propellants were 80% by weight. The antioxidant was BKF with concentration up to 2.5% by weight of the polymer. Iron oxide was added to some of the samples, and to one of these samples aluminium was also added.The results show that the dynamic OIT depends on the active antioxidant concentration, and useful calibration curves were obtained for the propellants with and without iron oxide. Concentrations of active BKF up to 1.5% by weight of polymer could be determined using this method. Aluminium content in the propellant had no effect on the results. The results also indicate that the isothermal OIT cannot be used for determination of the active antioxidant concentration.

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