EXPERIMENTAL CHARACTERIZATION OF THE STRENGTH OF HAND-LAMINATED AND VACUUM BAGGED QUASI-ISOTROPIC GLASS-EPOXY COMPOSITES AGAISNT THE ISO 12215-5

Abstract

Glass fibre reinforced polymer composites are the most common materials employed for the manufacturing of small crafts. Their hull construction and scantlings are governed by the ISO 12215-5. The latest version of the standard introduced a new methodology to assess the ultimate strength of composites laminates. The regression equations based on the fibre weight fraction of the former version have been replaced by a more detailed ply-by-ply analysis. However, no validation data is available to ascertain the relevance of the default ultimate strengths provided by the ISO 12215-5:2019. This paper employs destructive testing to experimentally characterize the ultimate flexural, tensile and compressive strength of a quasi-isotropic glass-epoxy laminate. Experiments were undertaken in accordance with the ISO 178 for flexural properties, the ISO 527-4 for tensile properties, and the ISO 14126 for compressive properties. Two manufacturing techniques are investigated, namely hand lamination and vacuum bagging. The former represents a cheaper and therefore more common manufacturing option, while the latter is representative of an advanced manufacturing process. The key results show that the ISO 12215-5:2019 default ultimate strengths for the quasi-isotropic composite laminate tested are (i) conservative for the ultimate flexural strength, (ii) appropriate for the ultimate tensile strength, and (iii) optimistic for the ultimate compressive strength, especially for vacuum bagged samples, with the main cause identified as the value of the ultimate compressive breaking strain for chopped strand mat. These findings provide validation data for the ISO12215-5:2019. They may inform designers, compliance assessors and policy makers in the selection of relevant factors of safety for composite structures, and it is anticipated the results may contribute to future improvements in small craft regulations.