Mode I Fracture Behaviour on the Growth Ring Scale and Cellular Level of Spruce (Picea abies [L.] Karst.) and Beech (Fagus sylvatica L.) Loaded in the TR Crack Propagation System

Abstract

Summary Crack propagation in wood is strongly influenced by the microscopic structure of the material. The relationship between structure and function with regard to damage and fracture behaviour can only be understood with a sufficiently fine level of examination. An experimental approach to perform micro-wedge splitting tests on spruce and beech inside the chamber of an Environmental Scanning Electron Microscope and under atmospheric conditions is presented. The specimens are loaded in mode I in the TR crack propagation system. Based on the load-displacement diagram, the characteristic parameters of fracture energy, critical load and initial elasticity are determined. The load and displacement data for the in situ experiments are related to the obtained ESEM images and allow a discussion of the fracture process on the cellular level. Density was found to be an important factor for fracture mode and several crack arresting phenomena depending on the variation of elasticity could be identified.