Modelling of moulded hole load-carrying mechanisms in GFRP composites with the use of a two-phase material model

Purpose This study aims to investigate the potential of moulded holes manufactured in fibre-reinforced composites before curing without cutting the reinforcing fibres. Moulded holes can be considered as an alternative to drilled holes. This research evaluates the advantages of the moulded holes over their drilled counterparts, contributing to deeper understanding of the strength and failure mechanisms of both types of holes. Design/methodology/approach The strengths of the moulded and drilled holes manufactured in two types of glass-epoxy composites reinforced with twill fabrics with unit weights of 163 g/m2 and 280 g/m2 were assessed in open-hole tests. Additionally, strain fields around the holes were measured with the use of digital image correlation. The results of a two-phase finite element model designed for modelling moulded holes in the scope of this work were verified by comparison to the experimental results. Findings The results of the experiments show significantly higher open-hole strength of moulded holes than drilled holes made in glass fabric-reinforced epoxy composite (42.6% and 29.8% in the case of the two investigated reinforcing fabrics). The two-phase finite element model designed in the scope of research was successfully verified by the comparison with the digital image correlation measurements and confirmed that strains both in fibres and in matrix are lower in the case of moulded than drilled holes. Analysis of the results revealed also that the strain concentrations in the matrix initiate failure in the case of both types of holes. Originality/value This research offers a novel perspective on the topic of manufacturing holes in fibre-reinforced composites. Its results confirm that the moulded holes have the potential to replace drilled holes used in the bolted joining of such composites. Moreover, the proposed simple numerical model allows a thorough understanding of the behaviour of moulded holes and, thus, constitutes a useful tool for their further improvement and application in aerospace engineering.