Influence of water on the nanoindentation creep response of Nylon 6

A nanoindentation system fitted with a fluid cell has been used to probe the influence of water on the nanoindentation creep response of commercial Nylon-6 samples. Measurements on samples taken while immersed in deionized water were compared with measurements under usual ambient (similar to 50% relative humidity) conditions. Water absorption reduces hardness by around 50% and elastic modulus by around 65%. The dimensionless creep parameter, A/d(0), where A is a constant and d(0) is the initial penetration at the start of the creep-hold period, is a measure of the proportion of time-dependent deformation compared with the total deformation. This parameter decreases significantly in water. We have suggested previously that A/d(0) correlates with tan delta. The observed reduction in A/d(0) when wet is consistent with a decrease in the tan delta peak due to a shift in the glass transition temperature when wet. (C) 2007 Wiley Periodicals, Inc.