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Fracture in the complex balsa cores of fiber-reinforced polymer (FRP) sandwich beams was analyzed. The cores were composed of high- and low-density balsa layers separated by a circular adhesive interface or FRP arch. The balsa layers were cut from panels which consisted of balsa blocks adhesively bonded together. Failure in the beams was initiated by cracks propagating through the balsa core thickness. The crack locations could be predicted using the Tsai-Wu failure criterion. Cracks initiated in the lowest density blocks due to their low fracture toughness. In mixed-mode fracture, crack propagation in the radial longitudinal (RL) plane prevailed due to the low fracture toughness in RL fracture of Mode I. In pure Mode II, propagation occurred in the RL and TL (transverse longitudinal) planes to the same extent since the toughness in RL and TL fracture is similar. Cracks were not able to propagate through the transverse adhesive joints between blocks if the bonding was good. If however the bonding was poor, interface failure occurred and cracks could propagate through the adhesive layer. (C) 2014 Elsevier Ltd. All rights reserved.

The span limits of two glass fiber-reinforced polymer (GFRP) bridge concepts involving GFRP- balsa sandwich plates are discussed. The sandwich plates were either used directly as slab bridges or as decks of a hybrid sandwich-steel girder bridges. In the latter case, the potential of the sandwich decks to replace reinforced concrete (RC) decks was also evaluated. Taking the limits of manufacturing into account (800 mm slab thickness), maximum bridge spans of approximately 19 m can be reached with FRP-balsa sandwich slab bridges, if a carbon-FRP (CFRP) arch is integrated into the balsa core. Above this limit, hybrid sandwich-steel girder bridges can be used up to spans of 30 m. RC deck replacement requires timber and steel plate inserts into the balsa core above the steel girders. GFRP-balsa sandwich slabs or decks exhibit full composite action between lower and upper face sheets.