Effect of crack size, thickness and span on the transverse mode I fracture characteristics of laminated flattened-bamboo lumber

To study the fracture characteristics of laminated flattened-bamboo lumber (LFBL), a transverse mode I fracture test was carried out on a single-edge notched (SEN) specimen. The failure of the specimen was analyzed at the macroscopic and microscopic levels. According to the analysis of P-CMOD curves, it was found that the entire fracture process could be divided into a linear stage, a softening stage and a failure stage, showing nonlinear elastic characteristics. Therefore, the fracture toughness KIC and tensile strength ft of the specimens were calculated by the boundary effect model (BEM) based on the nonlinear elastic fracture mechanism (non-LEFM). According to the calculation results, the influence of size change on fracture toughness KIC was analyzed. On this basis, this paper recommended the specimen size conditions for testing the mode I fracture toughness KIC of SEN specimens of LFBL in LT plane, i.e., S/W ≥ 4 and B ≥ 25 mm, thereby reducing the data dispersion caused by the change of specimen size. Finally, the mode I fracture toughness was obtained: KIC = 429.490 MPa·mm1/2.