Mode II initiation fracture toughness analysis for wood obtained by 3-ENF test

Abstract

The mode II initiation fracture toughness of wood measured from the three-point bend end notched flexure (3-ENF) test was analyzed by the eight conventional analysis methods: the elementary and Timoshenko’s beam theory methods, three of the Williams end correction methods, two compliance calibration methods, and the crack shear displacement (CSD) measurement method. In addition to these methods, the strain at the bottom of the midspan was measured, as was the loading-line displacement and critical load for crack propagation, and the initiation fracture toughness was obtained by the combination of loading-line and load-longitudinal strain compliances and critical load for crack propagation, which is named the “compliance combination method”. Among the analysis methods examined here, the compliance combination method is advantageous in that the fracture toughness is determined accurately by the 3-ENF test alone without requiring separate tests or special devices designed for the test. When considering the practical operation of measuring the mode II initiation fracture toughness of wood, the compliance combination method is quite suitable for the data analysis method.