Analysis of preconditioned glass fibre reinforced composite sandwich I-beams in bending

The flexural mechanical behaviour of various composite sandwich I-beams has been investigated under quasi-static loading. Both intact and preconditioned I-beam specimens were examined. The intact I-beams had two different support spans. The preconditions included central voids and remote debonds, both embedded at the flange-web intersections, whereas remote, barely visible impact damage (BVID) was introduced on the flange surfaces. It was found that the behaviour of the present I-beams was nearly linear until ultimate failure approached, and that the load-bearing capability exceeded the design requirement, irrespective of the preconditions. The flexural rigidity of the intact I-beams calculated by using the lamination theory compared well with the experimental value. The analytical predictions for maximum deflections and maximum tensile strains were in reasonably good agreement with the respective experimental measurements, It was found that neither the central voids nor the remote debonds or BVID had a significant effect on the flexural behaviour. The process of structural failure was extremely complex and was affected to a greater extent by the relatively low mechanical properties of the polymethacrylimide (PMC) foam core. It was shown that foam compression and local web skin wrinkling were the major failure mechanisms, irrespective of the preconditions.