Stiffness Evaluation of Neoprene Bearing Pads Under Long-Term Loads

摘要

The objective of this project was to evaluate the interaction between the shear modulus of steel reinforced neoprene bearing pads and shear strain rate. The following interactions related to variations in the shear modulus were investigated for pads with various shape factors: product approval strain rate vs. short-term field strain rates, short-term rates vs. long-term field strain rates, reduction in shear modulus due to load cycles, and effects of compressive stress. Forty-two tests were performed using test equipment designed to apply a shear strain at a variety of rates (50% shear strain at rates from 45 seconds to 90 days) while applying a sustained compressive load. Test results indicated: the shear modulus reduced on average 7% when tests were performed using the short-term field strain rates of 50% over 12 hours instead of the product approval strain rates of 50% over 30-60 seconds, there was essentially no reduction in shear modulus using long-term field loading rates of 50% over durations up to 90 days vs. short-term field strain rates, the shear moduli for pads that had never been load cycled were approximately 12% higher than cycled pads, and 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). Recommendations for upper and lower limits on the shear modulus to be used in design are included.