Mixed-mode Ⅰ/Ⅱ fracture behavior of parallel neosinocalamus affinis bamboo strand lumber using the modified Arcan fixture

Abstract

This study investigated the mixed-mode I/Ⅱ fracture behavior of parallel neosinocalamus affinis bamboo strand lumber (PNABSL) using experimental and numerical methods, focusing on the effects of crack width ratio (λ) and loading angle (θ) on fracture behavior. Finite element analysis developed non-dimensional stress intensity factors f_I(λ, θ) and f_Ⅱ(λ, θ). The results indicated that f_I(λ, θ) was highly sensitive to the crack width ratio and decreased with increasing loading angle, while f_Ⅱ(λ, θ) was nearly independent of crack length when θ < 75°. Three macroscopic failure modes were observed: fracture failure, bolt hole failure, and shear failure parallel to fibers, with fracture surfaces varying from torn (0° ≤ θ ≤ 60°) to hackly (75° ≤ θ ≤ 90°). Testing with λ ≥ 0.5 is recommended to avoid undesirable failure modes. The critical stress intensity factors for PNABSL were determined as K_IC = 25.05 MPa·mm^1/2 and K_ⅡC = 77.95 MPa·mm^1/2. Compared to wood, PNABSL showed higher K_IC and K_ⅡC. The mixed-mode fracture criterion coefficients for PNABSL were established as m = 0.7 and n = 0.8.