Fracture of wood under mixed mode loading I. Derivation of fracture criteria

A mixed mode I/II fracture criterion applicable to cracks oriented both alo ng and across the fibres in wood is derived within the framework of linear elastic fracture mechanics. The use of a common fracture criterion for both types of cracks is made possible by the fact that cracks in wood generally propagate along the fibres, irrespective of both the original crack orient ation and the degree of mode mixity. The derived criterion is simple, and c ontains a single material dependent fracture parameter. The applicability o f the fracture criterion to spruce (Picea abies) is experimentally validate d in part two of the paper. (C) 2001 Elsevier Science Ltd. All rights reser ved.