Mixed-mode I/II fracture performances of glued laminated bamboo in the in-plane longitudinal direction

Considering that glued laminated bamboo components usually fail because of the longitudinal cracks under combined tensile/shear loading, mixed-mode I/II fracture tests were conducted on two kinds of glued laminated bamboo boards in the in-plane longitudinal direction by Arcan test method: laminated bamboo lumber (LBL) with thick-layer unidirectional-arranged bamboo strips and glued laminated bamboo (glubam) with thin-layer bidirectional-arranged bamboo strips. on the basis of Wu criterion for mixed mode fracture of wood, the mixed-mode I/II fracture envelops of LBL and glubam are constructed by curve fittings on the calculated fracture toughness components and the pure mode-I and mode-II fracture toughness. The results show that the small quantity of transverse bamboo fibers change the fracture mode in the in-plane longitudinal direction from short and quick matrix-dominated brittle failure of LBL specimens into long and slow fiber and matrix-dominated quasi-ductile failure of glubam specimens. In response to the in-plane longitudinal crack, only 1:4 of transverse fibers to longitudinal fibers can provide about 6 times of the pure mode-I fracture toughness, 1.4 times of the pure mode-II fracture toughness and more than 6.5 times of the area within the mixed-mode I/II fracture envelope.