Mode III fracture energy of wood composites in comparison to solid wood R. J. A. Ehart, S. E. Stanzl-Tschegg, E. K. Tschegg Abstract A simple experimental setup for mode III and mixed mode (I + III) fracture tests with anisotropic materials under steady state crack propagation has been developed. Load-displacement curves can be recorded up to the complete separation of the specimen. From the load-displacement curves several mechanical material parameters can be derived. The tests have been performed for solid wood and different wood composites, being PARALLAM Ò PSL in different orientations, particleboard and INTRALLAM Ò LSL, and the fracture behaviour is characterised by the speci®c fracture energy. Introduction In comparison to many other fracture mechanical testing setups like tensile tests one feature of the (wedge) splitting concept for mode I testing (Tschegg, 1986) is the stability of crack propagation. If a stiff testing machine and loading device as well as a proper specimen geometry is used (Ehart et al., 1996a) crack propaga- tion can be stopped at any state by unloading. In this case the full load-dis- placement curves can be recorded not only of ductile but especially of brittle and quasi brittle materials before complete separation of the specimen takes place. These curves contain a lot of information on the fracture behaviour of the investigated material, and its characterisation according to the fracture energy (Nakayama, 1965) or crack resistance concept (Sakai and Bradt, 1986, Stanzl- Tschegg et al., 1995) can be carried out. In addition, using iterative FE methods Wood Science and Technology 33 (1999) 391±405 Ó Springer-Verlag 1999 Received 12 March 1997 R. J. A. Ehart, E. K. Tschegg (&) Institute of Applied and Technical Physics, Technical University of Vienna, Karlsplatz 13, A-1040 Wien, Austria S. E. Stanzl-Tschegg Institute of Meteorology and Physics, University of Agricultural Sciences of Vienna, Tu Èrkenschanzstraûe 18, A-1180 Wien, Austria The authors gratefully acknowledge ®nancial support of the biaxial testing machine by the Austrian National bank (research project nos. 4917 and 650915). They also thank Trus Joist McMillan for supplying the testing material and Dir. Donald Sharp for his helpful cooperation. 391