Fracture Toughness of 7075-T6 and -T651 Sheet, Plate, and Multilayered Adhesive-Bonded Panels

Abstract

Fracture-toughness tests have been made of 7075-T6 sheet and -T651 plate and of multi-layered panels of the sheet and plate. The nominal net fracture strength and the critical fracture-toughness parameters (Kc and Gc ) of multilayered adhesive-bonded panels are greater than those of sheet or plate of the same total thickness, because the individual layers may fracture independently, each developing shear surfaces. The fracture strength and critical stress intensity factor, Kc , for a 0.5-in. thick panel made up of eight layers of 0.063-in. sheet are approximately twice those of 0.5-in. plate. Multilayered metallurgically bonded panels do not exhibit any advantage over sheet or plate of the same thickness, if the metallurgical bond retards shear-surface formation on the individual layers. The plane-strain stress-intensity factor, determined at pop-in on multi-layered adhesive-bonded or metallurgically bonded panels, is independent of thickness or number of layers.