Fracture of Solid Wood: A Review of Structure and Properties at Different Length Scales

This paper presents a review of the fracture literature of solid wood. The review is not exhaustive and is focused on the structure and properties of wood at different length scales. Fracture of wood has been examined in all pure modes as well as mixed-Mode I and II and all directions—radial, tangential, and longitudinal. The literature has been studied at a variety of levels from molecular through cellular and growth ring to macroscopic. The major conclusions are that fracture toughness perpendicular to the grain is greater than that parallel to the grain and Mode II is greater than Mode I, within a given species. Also, fracture toughness increases with increasing density and strain rate. Defects typically reduce the strength and fracture toughness, with edge defects having a greater effect. Finally, the fracture toughness of solid wood reaches a maximum between 6 to 8% moisture content. The paper discusses how these macroscopic observations are related to the chemical composition and micro/meso-structure of wood