Creep of thermoplastics under uniaxial, shear, and hydrostatic stress conditions

Abstract

Creep data obtained from p.v.c., p.m.m.a., and p.p. sheet in uniaxial tension and compression, shear, and hydrostatic compression were used to test analytical correlating procedures. It was shown that shear and uniaxial creep could be closely related through the concept of shear stress and shear strain on octahedral planes. Volume strain in uniaxial creep was expressed in terms of the co-ordinate strains and used to predict volume strain in hydrostatic compression. These correlating procedures were only effective if due allowance was made for the different creep responses in simple tension and compression for each of these materials. It was also shown that the relations between viscoelastic compliances and strain ratio, which are stress- and time-dependent, have the same form as the relations between the linear elastic constants.