Nonlinear Viscoelastic Analysis of the Torque, Axial Normal force and Volume Change Measured Simultaneously in the National Institute of Standards and Technology Torsional Dilatometer
Carl R. Schultesiz, G B. McKenna
For compressible materials, the mechanical response to a torsional deformation (at sufficiently large levels of deformation) includes the nonlinear effects of a compressive normal force along the axis of the cylinder and a radial expansion of the cylinder, in addition to the expected torque response. The NIST Torsional Dilatometer [Duran and McKenna, Journal of Rheology, 34, 813-839, 1990] has been used to measure simultaneously the torque, the axial normal force and the volume change in response to a torsional deformation. In stress-relaxation experiments with an epoxy cylinder just below its glass transition temperature, the torque and normal force decay monotonically, but the volume change associated with the torsion shows an extended relaxation behavior with significant non-monotonic decay at the lowest temperature investigated. The measurements are modeled with a series solution for torsion of an elastic, compressible material [Murnaghan, Finite Deformation of an Elastic Solid. Wiley, New York., 1951]. The elastic solution is adapted for viscoelastic behavior by assuming that isochronal data can be treated as equilibrium elastic data, following a suggestion of Rivlin [Quarterly of Applied Mathematics, 14, 83-89, 1956].
and McKenna, G.
Nonlinear Viscoelastic Analysis of the Torque, Axial Normal force and Volume Change Measured Simultaneously in the National Institute of Standards and Technology Torsional Dilatometer, Journal of Rheology, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=851916
(Accessed June 6, 2023)