Fracture of wood under mixed mode loading II. Experimental investigation of Picea abies

An experimental investigation of mixed mode I/II fracture in Norway spruce (Picea abies) is presented. Mixed mode fracture is studied in two principal crack systems, RL and LR, in which the crack planes extend along and acros s the wood fibres, respectively. The investigation shows that onset of mixed mode cracking can be predicted with a very simple fracture criterion in both these crack systems. However, the applicability of the fracture criterion to cross-fibre cracks is limit ed to configurations, in which the crack tip T-stress, i.e. the non-singula r stress acting parallel to the crack plane, is low. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.