Comment on Mode II critical stress intensity factor of wood measured by the asymmetric four-point bending test of single-edge-notched specimen while considering an additional crack length, of H. Yoshihara in Holzforschung

Abstract

The results of the here discussed article of Yoshihara (2012), are unsatisfactory and need to be reconsidered. The existence of two critical stress intensities is postulated, which may differ a factor 3 to 4 from each other. A questionable push up of the lower data-curve, as given by Fig. 3 of Yoshihara (2012), may diminish this difference, but what to do with the conclusion that the critical stress intensity is effectively obtained. It is not mentioned when the high, and when the low values apply and why. Any conclusion should be based on theory and the theoretical explanation of the in Yoshihara (2012) and (2008) mentioned data, is given in van der Put (2012), because these data provide a confirmation for mode II softening like behavior. Based on this theory, correction is necessary of the interpretation and conclusion of Yoshihara (2008). This discussion is given here in the light of the achievements of wood mechanics.