Measurement of mode II fracture toughness of wood by the end-notched flexure test

Abstract

We examined the applicability of end-notched flexure (ENF) tests for measuring the mode II fracture toughness of wood. Western hemlock (Tsuga heterophylla Sarg.) was used for the specimens. The fracture toughness at the beginning of crack propagationG IIc and that during crack propagationG IIR were calculated from the loadloading point compliance and load-crack shear displacement (CSD) relations. The obtained results were compared with each other, and the validity of measurement methods were examined. The results are summarized as follows: (1) The value ofG IIc increased with the increase in initial crack length. When measuringG IIc by ENF tests, we should be aware of the dependence ofG IIc on the initial crack length. (2) The value ofG IIR initially increased with the crack length, and it reached a constant value. (3) Measurement of the CSD is recommended when obtainingG IIR because the crack length, which has a great influence on theG IIR calculation, is implicitly included in the CSD. (4) We found that the crack length during its propagation should be evaluated by the final crack length.