Intralaminar and interlaminar fracture characterization in glued-laminated timber members using image analysis

This paper is concerned with the characterization of Mode I and Mode II fracture present in glued-laminated (glulam) timber members. In a typical glulam timber member, fracture can occur within each lamina (i.e., intralaminar fracture) or at the interface of two laminae (i.e., interlaminar fracture). Both the intralaminar and interlaminar fracture was investigated through an experimental study, where the double cantilever beam test for Mode I fracture and the end-notched flexure test for Mode II fracture were performed to a series of specimens. A salient feature of the intralaminar fracture in glulam timber members lies in the direction normal to the crack propagation plane. It is often the case that this direction neither coincides with the radial direction nor the tangential direction of the wood. Consequently for each intralaminar specimen tested, an image analysis was carried out to identify the relevant growth ring orientations, which were in turn represented by an angle. Analogous procedures were also utilized to associate three angles indicating growth ring orientations to each interlaminar specimen. After the specimen failure, crack tip morphology was analyzed by scanning electron microscopy micrographs. The critical loads used in the computation of the fracture energies were identified from the recorded load-versus-displacement curves. Further, statistical analyses were implemented to examine the obtained intralaminar Mode I and Mode II fracture energies with regard to different growth ring orientations.