Time-dependent behaviour of fiber reinforced polymeric composites

Sammanfattning: The presented thesis contains results of experimental and theoretical studies of the time dependent processes in fiber composites. The first part of the thesis is dedicated to unidirectional fiber reinforced composites. Glass fiber laminates are tested and analyzed. Performed creep tests show that the total strains may be separated in linear elastic response, linear viscoelastic strains,permanent time independent strains and permanent time dependent strains. The correspondence principle in Laplace domain and micromechanical model developed by Hashin are used. The time dependent compliance matrix of the resin is back-calculated using test data. Then the model and the obtained resin data are used to predict creep behavior of laminates. The second part of thesis deals with glass mat reinforced thermoplasts (GMT). Creep tests and relaxation tests are performed on polypropylene and GMT specimens. It is proved that both materials in the range of used loads may be considered as linear viscoelastic and description of viscoelastic properties of both materials is obtained. The icromechanical model developed in the first part of thesis is generalized for the case of non-unidirectional fiber distribution. For this reason the GMT material is considered as consisting of an infinite number of unidirectional plates with a given fiber orientation distribution and laminate theory approach is applied.