Accelerated thermal aging of grease-based magnetorheological fluids and their lifetime prediction

In this article, the effect of elevated temperature on the rheological properties of grease-based magnetorheological fluids (G-MRFs) with the focus on long-term storage lifetime has been investigated. These G-MRF samples were subjected to accelerated heat aging process for the estimation of thermal stability and useful lifetime prediction. The well-known Arrhenius-Weibull relationship with a modified Powell-Beal conjugate gradient (CGP) algorithm was employed to model the 'life in service' for the achievement of possible life distribution at different temperature conditions. By defining the failure criteria of G-MRF samples as a maximum reduction of either viscosity or shear stress by more than 10%, the underlying degradation mechanism was revealed through Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) analysis. Based on the statistical inference from accelerated life test (ALT), the life expectancy of G-MRF under nominal operating temperature is estimated to be 15.2 years, which outpaces the capability of most industrial applications. Experimental results showed that the performance of shear stress is more likely to degrade under long-term treatment of high temperature in comparison with low temperature. Thus, it is suggested to store the G-MRF at relatively low temperatures for longevity extension and reliability improvement.