A Strategy for the Life Prediction of Polymer Matrix Construction Components: Strain-Stiffness Evolution or Strength-Damage Development?

摘要

Polymer matrix composites exihibit a time dependent behaviour due to the viscoelastic nature of the matrix. This behaviour is also influenced by the environmental conditions; especially temperature changes and moisture uptake and diffusion. The loading conditions may change the interaction level between matrix and fibres as well as between lamina. Internal transformations in the polymer matrix, known as physical and/or chemical ageing, changes the properties of the matrix and as consequence the properties of the composite. For reliable applications of polymer matrix composites it is necessary to arrive at the prediction of stiffness and strength evolution in order to guarantee a safe residual behaviour under a complex mechanical loading history in interaction with environmental variations after an imposed life time. The analysis of the stress-strain behaviour allows us to predict the stiffness evolution. The strength evolution can be obtained from a limit criterion with time, stress and environmental dependent characteristics or by the analysis of damage initiation and development. A nonlinear viscoelastic-viscoplastic model is used for the stiffness prediction under quasi-static loading conditions. This model has to be corrected for interactions between dynamic and quasi-static loadings. A damage analysis based on the heterogeneisation of the strain fields observed experimentally by some full field optical method is able to model the strength degradation. Combination of stiffness and strength evolutions give us the basis for the prediction of the limits of residual structural integrity.