Applicability of classical isotropic fracture mechanics specimens to wood crack propagation studies

Abstract

Different specimen types (double cantilever beam: DCB, compact tension: CT, single edge notched in tension: SENT) have been numerically studied (with special finite elements) for ten wood species and for cracks situated in a material plane of symmetry (the crack is denoted xy with x the direction of the normal to the crack plane and y the direction of propagation). Single-edge notched speciments used in RL, TL directions appear to be insensitive to the orthotropic properties of the material. So, calibration known for isotropic materials can be used in stress intensity factor calculations. In transverse directions (LT, LR), such specimens could be used with a double height. Small differences, but depending on the species tested, have also been obtained in TR and RT directions. Calibration of CT specimens of an isotropic material cannot be used even in TL and RL directions. A calibration acceptable for all the studied species is proposed. A different calibration is also given in the TR direction. It is suggested, however, not to use specimens in the RT direction without a calibration specific for the wood species tested. DCB specimens could be used in RL, TL and TR directions with a calibration which is a function of elastic moduli. This calibration is obtained from analytical calculations. In other directions, these specimens do not offer any experimental interest.