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Creep experiments and examples for viscoelastic material under combined stress with abrupt changes in state of stress
Author(s) -
Onaran K.,
Findley W. N.
Publication year - 1965
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760050402
Subject(s) - viscoelasticity , materials science , creep , superposition principle , torsion (gastropod) , constitutive equation , hyperbolic function , mechanics , stress (linguistics) , composite material , thermodynamics , mathematical analysis , mathematics , physics , medicine , linguistics , philosophy , surgery , finite element method
Creep experiments under combined tension and torsion loading are reported for tubular specimens of polyvinyl chloride copolymer. Experiments include a sequence of several combinations of tension and torsion on each specimen with abrupt changes between combinations, including reversal of sense of torsion, recovery and reloading after recovery. Results show a strong path and time dependence for the strain and for the direction of the strain‐rate vector at constant state of stress following a change in state of biaxial stress. The character of the results is described reasonably well by the Boltzmann superposition principle of linear viscoelasticity using a constitutive equation of the form:Examples are given of the use of this equation for common states of stress. Better agreement with the data is obtained from a similar but non‐linear equation employing hyperbolic sine functions of stress.