Magnetorheological fluid durability test—Iron analysis

This report describes chemical changes and the methodology to detect such changes in iron particles from extracts of certain magnetorheological fluids (MRFs) which had been subjected to durability testing in an MRF fan clutch. Samples of MRF subjected to 540 and 108 h of service in a MRF fan clutch on a test stand were characterized along with neat and unused materials for comparison. The results indicated that: the iron subjected to durability testing had oxidized; a portion of the iron oxides were crystalline magnetite; and the oxides were concentrated at the perimeter of the smaller iron particles although both large and small particles were oxidized. This oxidation may explain the gradual loss of fan clutch torque capacity observed during the 540 h durability test.