抄録
Much efforts have been done to understand a constitutive equation of solid polymers. But much attention has not been paid to stress-strain behavior after un-loading. The stress-strain behavior were investigated at uniaxial and biaxial stresses for some paths with strain or stress reversal using polyethylene. The followings are interesting for studying the constitutive laws obtained from the present study: at a stress relaxation (or creep) test after unloading, the stress rate (or the strain rate) changes its sign during the test depending on the test condition (anomalous behavior after unloading; ABU), and 2) under biaxial tension creep test after unloading, only the strain in the direction along which the applied stress was unloaded showed ABU.
