The effect of blast loading on composites that contain sustainable materials

In the pursuit of global environmental sustainability, bio-based resins, and natural fibres as reinforcements in Fibre Reinforced Polymer (FRP) composites offer potential benefits, and some of these can be used in different applications particularly when strength is of secondary importance (such as automotive, architecture, and mass-transportation industries). However, there is a constant possibility of explosive threats, and little is known about the blast response of these materials. This study focusses on the effect of blast loading on composites with sustainable constituent materials. Seven different FRP composites were examined. Two were chosen as control materials, namely glass fibre reinforced epoxy composite and a common medium density fibreboard (MDF). The five sustainable materials were: vacuum infused flax fibre reinforced epoxy using both bio-epoxy and conventional epoxy, vacuum infused jute fibre reinforced epoxy, flax fibre reinforced epoxy made using hand lay-up and glass fibre epoxy manufactured using a bio-epoxy. These composites were subjected to quasi-static and blast loading conditions. Initially, some of the material properties of the seven composite systems were characterised though a series of quasi-static tensile, flexural and interlaminar fracture tests. Blast testing was undertaken on a ballistic pendulum facility, capable of measuring the impulse imparted by the plastic explosive. The glass fibre reinforced composites had better blast resistant properties in comparison to natural fibre composites, following the trends observed during quasi-static testing. Delamination was observed on the glass fibre reinforced composites and the damage tended to increase progressively. Large amounts of inelastic deformation, surface and through-thickness cracking were observed on the natural fibre composites. The jute fibre reinforced composites tended to have a sudden destructive failure whereas the flax fibre reinforced composites and, to some extent, MDF sustained progressive damage. Substituting the epoxy resin for the more sustainable bio-based resin had little effect on the blast resistance for both glass and flax fibre reinforced composites, which is encouraging because this suggests that a sustainable resin can be substituted in those panels without significant degradation in blast protection properties. The manufacturing method played a role for the flax fibre reinforced composites, with hand lay-up specimens exhibiting a lower level of protection and inconsistent properties compared to the vacuumed infused panels. The results also indicated that the addition of more glass fibre plies enhanced the blast resistance considerably. Of the composites tested, the best performing composite that takes sustainability into account was the glass fibre reinforced bio-based epoxy composite. The results of the experimental study presented discusses the blast behaviour of these materials which are relevant to engineers considering alternative sustainable materials in various applications where explosive loading is a threat