Determination and influential factors of fracture toughness in unidirectional laminated bamboo-composite using double cantilever beams and single-edge notched bend tests

Abstract

This paper studied two testing methods for determining the matrix-dominate fracture toughness in the unidirectional bamboo laminate panels, using double cantilever beam tests and single-edge notched bend tests. For single-edge notched bend tests, an isotropic solution was proposed to calculate the fracture toughness in which only the load-CMOD curve is required. In this isotropic solution, when calculating the energy release rate G Ic by G Ic = (K Ic ) 2 /E, the modulus of elasticity E can be directly obtained from the experimental load-CMOD curves, the pre-determination of Young’s modulus E x , E y , shear modulus G xy and Poisson’s ratio υ xy , υ xy is unnecessary for orthotropic materials. The results of modulus of elasticity E, the stress intensity factor K Ic , and energy release rate G Ic using the isotropic solution were compared to those using an orthotropic solution; it revealed that the isotropic solution could be well applied to unidirectional bamboo laminate panels with errors under 2.7%. The isotropic solution for single-edge notched bend tests was also verified by comparing the results to those obtained from double cantilever beam tests; it turned out that the energy release rate values determined by the two testing methods agreed well with each other. Moreover, the influence of initial notch width, initial notch to depth, and specimen depth on the fracture toughness was investigated to put forward a practical testing method to obtain the size-independent fracture toughness of unidirectional bamboo laminate panels by single-edge notched bend specimens.