Methodologies for the investigation of the mechanical behaviour of polyvinylchloride foams

Closed-cell polyvinylcloride (PVC) foams are used as core materials for sandwich composites in challenging applications such as wind turbine blades, in which a wide range of multiaxial loads are involved. By a review of the relating literature, still more analyses are needed for a throughout understanding of the mechanical behaviour of PVC foams and particular attention has to be dedicated on the concerning methodologies. The present work aims to give a contribution in this field by the execution of a great amount of experimental tests on different types of closed-cell PVC foams. The first part of this work focuses on the study of the compressive properties of PVC foams and, more precisely, several methods for the determination of the compressive modulus are described and conducted. Such methods are closely linked to the procedure for the strain measurement, that is achieved either by the digital image correlation or by the output displacement data of the universal testing machine, which give back the local strains and the global strains, respectively. The second part addresses the multiaxial behaviour of PVC foams by proposing a yield function which has been successfully applied for other materials. The deformation mechanism under multiaxial loading has been analysed through the three-dimensional digital image correlation performed by a new 8-camera system. The enhancement of this method is described in great detail and the resulting deformation bands are explained for each loading case. The present work focuses on the understanding of the mechanical behaviour of the material as well as on the application of methodologies.