MODE I FRACTURE PARAMETERS AND FAILURE CHARACTERISTICS OF YEW AND SPRUCE LOADED IN THE RT AND TR CRACK PROPAGATION SYSTEM BY MEANS OF A MICRO WEDGE SPLIT-TING TEST

摘要

A micro wedge splitting test was performed with yew and spruce specimens oriented in the RT and TR crack propagation direction. Characteristic fracture parameters (initial slope, critical load, specific fracture energy) were determined; the crack path was evaluated by means of scanning electron microscope images. Yew specimens turned out to be stiffer and stronger than spruce. Differences between both species regarding the fracture behaviour were ascribed to variability of micro structural features such as cell wall I lumen aspect ratio. Pronounced fiber bridging of yew specimens was remarkable which might play an important role as toughening mechanism.