On the Interlaminar Fracture Toughness of Some Softwood Cores

ABSTRACT: The interlaminar fracture toughnesses of balsa and end-grain balsa cores with glass-reinforced plastics (GRP) face elements widely used as constructive members, has been investigated experimentally in this study. The interfacial fracture toughness is determined using a mode-I cracked sandwich beam (CSB) test. Some tests have been performed for the poplar (easily available because of its natural distribution along the coast of Turkey and more cost effective than balsa and its derivatives) in order to see if it is a viable alternative to balsa. Ayous, a low density wood, was also tested additionally to understand its interlaminar fracture behavior as a softwood core. It has been found that ayous, poplar, and balsa, classified as low density cores, have much lower fracture toughness values than end-grain balsa cores. To achieve lighter structures with high fracture toughness by using the cores investigated in this study, it can be seen that the best alternatives in due order are end-grain balsa, ayous, poplar, and balsa, respectively. KEY WORDS: softwood/GRP sandwich systems, fracture toughness, mode-I cracked sandwich beam test, balsa, end-grain balsa, poplar, ayous