Static behaviour of preconditioned glass-fibre-reinforced epoxy sandwich I-beams

The short-term mechanical behaviour of both intact and preconditioned glass -fibre-reinforced composite sandwich I-beams has been investigated under qu asi-static loading. A high-strength and tough epoxy adhesive system has bee n used for bonding the flanges to the web section in the manufacturing of t he I-beams. Preconditions included both appreciable bonding defects such as voids and debonds and barely visible impact damage (BVID). While voids and debonds with selected sizes and locations were introduced at the flange-we b intersections directly associated with bonding, BVID was inflicted on the flange surfaces. It is found that halfway towards the peak load, the anti- symmetric buckling of the compressive flange occurs leading to some limited nonlinear behaviour and that its associated edge delaminations at the comp ressive flange-web intersection are isolated and make no direct contributio n to the ultimate failure of these I-beams. It is shown that the ultimate f ailure starts from the shear failure of the foam core in the sandwich web i nstead and ends with web skin wrinkling. It is demonstrated that under the current conditions, preconditions do not have an over-riding effect on the mechanical behaviour of I-beams and that the epoxy adhesive system is compl etely adequate. (C) 1999 Elsevier Science Ltd. All rights reserved.