Multiaxial failure surface of PVC foams and monitoring of deformation bands by three-dimensional digital image correlation

Closed-cell polyvinylchlorid foams are among the most used core materials for sandwich composites. Therefore, a deep knowledge of their multiaxial behaviour is fundamental. More precisely, a literature review proves the lack of investigations concerning combined tensile-torsional loadings. In the present work simple tests, namely tension, compression and torsion have been performed for determining failure loads. Afterwards, multiaxial tests have been executed by applying different percentages of the previously calculated failure loads as preload and subsequent superposition of torsion, keeping simultaneously the axial load constant. For each multiaxial test, failure data have been collected in order to construct the failure surface for the foam material. The whole specimen surface has been inspected by means of the three-dimensional digital image correlation, in order to detect the failure of the specimen, as well as the onset and the development of deformation bands. Monitoring of the specimen has been performed for each main loading case. Afterwards, the analysis of deformation bands has been coupled with stress-strain diagrams and linked with the arising of buckling or fracture and the instrinsic orthotropy of the foam. (C) 2019 Elsevier Ltd. All rights reserved.