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A model for non-linear creep in polypropylene.

Dean, G D; Broughton, W R (2008) A model for non-linear creep in polypropylene. Polym. Test., 26. pp. 1068-1081.

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Measurements of the creep behaviour of a polypropylene polymer under uniaxial tension have been modelled using a stretched exponential function with 4 parameters. Non-linear behaviour arises because one of the parameters, related to a mean retardation time for the relaxation process responsible for creep, is dependent on stress. Creep curves measured under a uniaxial tensile stress and a uniaxial compressive stress of the same magnitude are different. The differences can be described by relating the retardation time parameter to an effective stress that is determined by the magnitude of the shear component of the stress as well as the hydrostatic component. This analysis has then been generalised to enable expressions to be formulated for creep behaviour under an arbitrary multiaxial stress state. This requires an assumption that either the Poisson's ratio or the bulk modulus are independent of time. The validity of these assumptions has been evaluated through comparisons of predictions of creep under a pure shear stress with measurements which show that a time-independent Poisson's ratio is the better approximation.

Item Type: Article
Keywords: creep of polypropylene, creep model, non-linear behaviour, creep under multiaxial stress
Subjects: Advanced Materials
Advanced Materials > Materials Modelling
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4261

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