Shear Stiffness of Neoprene Bearing Pads under Long-Term Loads

Abstract

This research evaluated the interaction between the shear modulus of steel-reinforced neoprene bearing pads and the shear strain rate. The following interactions related to variations in the shear modulus were investigated for pads with various shape factors: product approval strain rates versus short-term field strain rates, short-term field strain rates versus long-term field strain rates, reduction in shear modulus due to load cycles, and compressive stress. Forty-two tests were performed with test equipment designed to apply a shear strain at a variety of rates (50% shear strain at rates from 45 s to 90 days) while applying a sustained compressive load. Test results indicated that the shear modulus was reduced on average by 7% when tests were performed with the short-term field strain rates of 50% over 12 h instead of the product approval strain rates of 50% over 30 to 60 s, that there was essentially no reduction in shear modulus with long-term field loading rates of 50% over durations up to 90 days versus short-term field strain rates, that the shear moduli for pads that had never been load-cycled were approximately 12% higher than those of cycled pads, and that the effect of compressive stress agrees with previous work (i.e., the shear modulus decreases with increased compression particularly for bearings with low shape factors).