Wednesday, 13 October 2004 - 3:30 PM

This presentation is part of : Mechanics and Thermodynamics of Polymers

Prediction of long-term failure in glassy polymers

Leon E. Govaert, Edwin T.J. Klompen, Tom A.P. Engels, and Han E.H. Meijer. Eindhoven University of Technology, 513, Eindhoven, NL-5600 MB, Netherlands

Long-term failure is a major concern when polymers and polymer composites are employed in load-bearing structural applications. In general, time-dependent failure is governed by the onset of plastic strain localisation, similar to phenomena like crazing and necking observed during a uniaxial tensile test. Over the past 15 years, considerable effort has been directed towards the numerical simulation of strain localisation in glassy polymers. Several constitutive models have been developed and validated for this specific reason. In the present investigation it is shown that such approaches can be very useful in the analysis and prediction of creep rupture phenomena.

To illustrate this, the finite-strain deformation behaviour of quenched poly(carbonate) is examined using uniaxial compression tests, thus enabling the evaluation and characterisation of the post-yield behaviour including strain softening and strain hardening. An accurate description of this behaviour is obtained using a previously developed model. The observed behaviour appears to be independent of molecular weight, but strongly influenced by thermal history. To incorporate this influence, the evolution of the yield stress is studied as a function of ageing time, temperature and applied load. Within the constitutive model employed this is described with the evolution of a single state-parameter.

The model is subsequently employed to simulate the long-term creep response of polycarbonate. It is shown that the time scale on which ductile failure occurs is predicted very accurately. Moreover, the model surprisingly predicts the occurrence of the endurance limit that is observed in the experiments.

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