No abstract

Accelerated creep is a curious and poorly understood transient moisture effect. The creep rates of most hydrophilic materials increase greatly with moisture content. However, when these same materials are subjected to creep loads in cyclic humidity environments, they often exhibit much higher creep rates than in a constantly humid state. This is called accelerated creep. Previous experimenters reported that accelerated creep was less likely to occur in polymeric fibers. We demonstrate experimentally that this happened only because of their choice of humidity cycling parameters. New results are given for Kevlar, lyocell, nylon-6,6, and ramie fibers. Other paper scientists have argued that the absence of accelerated creep in single fibers supports a explanation based on fiber network effects for accelerated creep in paper. We argue here that accelerated creep is a more general phenomenon consistent with sorption-induced stress-gradient explanations.

In this study, the inverse relationship between lifetime and secondary creep rate was verified suggesting that shorter duration tests can be used to evaluate lifetimes. Also, the variability in creep rate was significantly lower than previous studies suggesting that using enhanced testing facilities could reduce required number of repetitions. A novel finding was an observed transition point in applied loading level where cyclic humidity conditions had the highest creep rates at low loads and constant high humidity conditions had the highest creep rate at high loads. Finally, it was determined that a standard moisture cycling history for a standard test protocol will be difficult to determine and the moisture sorption behaviour of each box type must be accounted for.

No abstract

No abstract