Influence of Crack Length on the Measurement of Mode II Initiation Fracture Toughness of Wood by Three-Point Bend End-Notched Flexure (3ENF) Test

The mode II initiation fracture toughness of wood was measured by the three-point bend endnotched flexure (3ENF) test for various crack lengths, and the dependence of toughness on the crack length was analyzed by the four conventional methods of data reduction : elementary beam theory, Williams end correction method, and two compliance calibration methods. In addition to these methods, the compliance combination method was used in which the fracture toughness is determined using the load-longitudinal strain compliance measured at the midspan as well as the loading-line compliance. In the four conventional data reduction methods, the dependence of aracture toughness on the crack length was significant. In contrast, the fracture toughness was appropriately determined by the compliance combination method, and it was independent of thecrack length. Therefore, the compliance combination method is advantageous in that the fracture toughness is determined accurately by the 3ENF test alone without requiring separate tests over a wide range of crack length.