Sealing force prediction of elastomeric seal material for PEM fuel cell under temperature cycling

Abstract

This paper is to study the sealing force of elastomeric seal material used for PEM fuel cell under temperature cycling. Stress relaxation and thermal stress of liquid Silicone rubber (LSR) seal material under temperature cycling is discussed. It is found that thermal expansion or contraction is the major contributor to the compressive stress developed in the LSR seal. The classical Maxwell model including the time-temperature shift can predict stress relaxation at a given temperature, but fail in calculation of thermal stress when there is temperature change. Experimental data show that material stiffness increased if the material had been aged at a higher temperature. This change of material stiffness was quantified experimentally and included in a modified Maxwell equation. The modified model appears to predict the sealing force accurately. A temperature profile was then used to demonstrate the sealing force development during startup, operation and shutdown periods of a PEMFC stack. Similar analysis can be applied to other polymeric materials under temperature variation which exhibit stress relaxation and material aging.