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Non‐linear creep of polymers under superimposed static and dynamic stress
Author(s) -
Akay G.
Publication year - 1975
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.760151108
Subject(s) - creep , power law , stress (linguistics) , materials science , power (physics) , constant (computer programming) , mechanics , strain (injury) , physics , mathematics , thermodynamics , composite material , computer science , statistics , medicine , linguistics , philosophy , programming language
The non‐linear creep of polymeric materials under super‐imposed static and dynamic stress is considered theoretically. The equation of state due to Green, Rivlin, and Spencer to‐gether with the power law of time dependence for the kernel functions as suggested by Nakada is assumed to characterize the non‐linear materials. Expressions for creep strain under constant static, oscillatory dynamic and superimposed static and dynamic stress are obtained in terms of the material constants and time dependent functions, called dynamic creep functions. It is shown that the creep strain due to dynamic stressing is damped as the number of stress cycles is increased. Damping is faster if the power law of time dependence is high. Expressions for the cumulative creep strain after multiple stress cycles are also obtained in terms of cumulative strain functions. All these functions are evaluated numerically at one thousand stress cycles. Finally, a special case of stress history is considered where the stress periodically reaches zero. It is shown that the ratio of the strains due to dynamic and static stressing can be characterized by the power law parameter when the mean stress is either very high or very low. Due to the slow damping when the power law parameter is small, the decrease of the strain ratio with number of cycles is slow compared to higher power law parameters.