Basic studies on fracture toughness of sugi and acoustic emission

Abstract

The technique of such a fracture mechanics is hardly adopted in a wooden architectural field though a lot of large-scale wooden buildings are constructed. Therefore, the accumulation of basic data about these fracture toughness is necessary. Especially, the research on the fracture toughness of sugi (Cryptomeria japonica D. Don) expected as a material for the structure are hardly performed. In this study, to obtain basic knowledge for the fracture toughness of sugi, compact tension (CT) specimens of six types (RL, TL, LT, RT, LR, and TR) with a different direction of the load and the crack progress in consideration of anisotropy were made from sugi. The fracture toughness tests with sugi CT specimen were conducted, and effects of the difference of both various CT specimens and load speed on the fracture toughness (K κ) were examined. In addition, acoustic emission (AE) generated during the test was measured, and the correspondence of the fracture toughness and AE was examined. The main results are summarized as follows: (1) for the sugi CT specimen in consideration of anisotropy, it was found that the specimen of two types of LR and LT was incompatible for the fracture toughness test in this study; (2) it was clear that the KIC of the sugi CT specimen shows constant values regardless of the load speed within the range of conditions in this test; (3) for the specimen of TR and RT that the crack progress direction was the vertical direction for the length direction, the K κ of TR was larger than that of RT; (4) the peaks in the AE average signal were admitted in the fracture process of the TR specimen and it corresponded to the position of the late wood part in progressing the crack. Therefore, AE technique is promising for the detection of the fracture process of the late wood part in the TR specimen.