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Magnetorheological elastomers (MRE) are interesting candidates for active vibration control of structural systems. In this study, spring elements consisting of magnetorheological elastomer were prepared and tested in dynamic compression to study the changes in their stiffness and vibration damping characteristics under the influence of a magnetic field. Aligned and isotropic magnetorheological elastomer composites were prepared using room temperature vulcanizing silicone elastomer as the matrix material and carbonyl iron as the magnetizable filler. Aligned MREs were prepared by curing the material under an external magnetic field. Aligned MREs were tested and the results were compared with isotropic composites with no preferred orientation. The mechanical properties of the MREs were tested in cyclic compression passively and with increasing magnetic flux density. The influence of the testing frequency and strain amplitude on the dynamic stiffness and damping properties was studied. It was noted that when measured in a magnetic field both the dynamic spring constants and the loss factor values of aligned MREs were increased compared to the zero-field values. The dynamic stiffness of aligned MREs increased with increasing testing frequency and it was tunable with magnetic flux density in the studied frequency range. The loss factor of aligned MREs was also tunable with the magnetic flux density but the absolute values also depend on the testing frequency. The dynamic stiffness of the aligned MREs measured in compression decreased with increasing strain amplitude, but the damping properties were not affected similarly. On the basis of these results, MREs are applicable as tunable spring elements for active vibration control.

The incidence and prevalence of subjects awarded disability pensions and the prevalence of subjects receiving free medicines because of rheumatoid arthritis were studied in a Finnish cohort of 1026 granite workers hired between 1940 and 1971 and followed up until 31 December 1981. The incidence of awards of disability pensions because of rheumatoid arthritis during 1969-81, the prevalence of rheumatoid arthritis on 31 December 1981, and the prevalence of subjects receiving free medicines for rheumatoid arthritis at the end of 1981 were significantly higher among the granite workers than in the general male population of the same age. Retrospective analysis ofthe records ofall patients with rheumatoid arthritis in the cohort showed a predominance of a severe, serologically positive and erosive form ofrheumatoid arthritis, usually with an age at onset of 50 or over.The possible aetiological or pathophysiological role ofgranite dust in rheumatoid arthritis may be based on the effects of quartz on the immune system.

An apparatus to measure the coefficient of kinetic friction (mu k) between the shoe sole and the underfoot surface was constructed, and a method including criteria to evaluate the risk of slipping during walking was developed. The apparatus is a prototype stationary step simulator capable of simulating the movements of a human foot and the forces applied to the underfoot surface during an actual slip, and the drainage capability of the contact surface between the shoe sole and the flooring when different lubricants or contaminants are used. The apparatus consists of a movable artificial foot controlled by a computer with the aid of three hydraulic cylinders. The frictional force (F mu), the normal force (FN) and their ratio (mu k = F mu/FN) are measured with a two-way force platform when the foot slides along its surface. Two separate gait patterns, heel-side (mu k 1) and sole-slide (mu k 2) gait pattern, are used for the evaluations. The method classifies studied shoe, lubricant and underfoot surface combinations into five slip resistance classes according to the measured mu k 1. The slip resistance assessments are specified with some complementary safety criteria, e.g., the ratio mu k 1/mu k 2. The reliability of the developed measurement method was assessed in an international comparison test. According to available results discussed in this paper, our method seems to be valid and the slip resistance measurements seem to be repeatable.