title: Hierarchical analysis of the degradation of fibre-reinforced polymers under the presence of void imperfections.
abstract: The subject of this work is the investigation of the influence of voids on the mechanical properties of fibre-reinforced polymers (FRPs) under compression loading. To specify the damage accumulation of FRPs in the presence of voids, the complex three-dimensional structure of the composite including voids was analysed and a reduced mechanical model composite was derived. The hierarchical analysis of the model composite on a micro-scale level implies the description of the stress and strain behaviour of the matrix using the photoelasticity technique and digital image correlation technology. These studies are presented along with an analytical examination of the stability of a single fibre. As a result of the experimental and analytical studies, the stiffness of the matrix and fibre as well as their bonding, the initial fibre orientation and the fibre diameter have the highest impact on the failure initiation. All these facts lead to a premature fibre-matrix debonding with ongoing loss of stability of the fibre and followed by kink-band formation. Additional studies on the meso-scale of transparent glass FRPs including a unique void showed that the experiments carried out on the model composites could be transferred to real composites. This article is part of the themed issue 'Multiscale modelling of the structural integrity of composite materials'.
authors.affiliation: Technische Universität Hamburg-Harburg, Institute of Polymer Composites, Denickestrasse 15, 21073 Hamburg, Germany wilfried.liebig@tuhh.de.
authors.forename: Wilfried V
authors.identifier: http://orcid.org/0000-0003-1855-6237
authors.initials: WV
authors.lastname: Liebig
authors.affiliation: Technische Universität Hamburg-Harburg, Institute of Polymer Composites, Denickestrasse 15, 21073 Hamburg, Germany.
authors.forename: Karl
authors.identifier: http://orcid.org/0000-0001-6521-0488
authors.initials: K
authors.lastname: Schulte
authors.affiliation: Technische Universität Hamburg-Harburg, Institute of Polymer Composites, Denickestrasse 15, 21073 Hamburg, Germany.
authors.forename: Bodo
authors.identifier: http://orcid.org/0000-0002-2734-1353
authors.initials: B
authors.lastname: Fiedler
keywords: analytical approach; effects of defects; fibre microbuckling; hierarchical analysis; polymer composites; voids