Nonlinear viscoelastic analysis of the torque, axial normal force, and volume change measured simultaneously in the National Institute of Standards and Technology torsional dilatometer

The NIST torsional dilatometer was used to make simultaneous measurements of the torque, axial normal force, and volume change in response to a torsional deformation of an epoxy cylinder that was aged into equilibrium at temperatures 5-10°C below the nominal glass transition temperature. In response to torsional deformation, the torque and axial normal force behaved as expected, decaying monotonically over time, but the volume change displayed an extended relaxation that varies with temperature and shows a significant nonmonotonic decay at the lowest temperature investigated.