The fracture mechanism of softwood via hierarchical modelling analysis

Abstract

A hierarchical model of softwood was developed to effectively analyze stress concentration and predict initial fracture of the wood cell wall under different loading scenarios. The results indicated that the simulated stress concentration regions of the tracheid wall approximately matched the experimental initial fracture locations. The stress concentration and initial fracture of the tracheid wall under longitudinal tensile stress occurred in the S2 layer. In the cases of pure longitudinal–radial (LR) or longitudinal–tangential (LT) in-plane shear loading, the highest stresses are observed in the S1/S2 interface and the S3 layer, but the initial fractures of the tracheids of the neutral layer under the LR or LT shear stress only occurred in the S1/S2 interface. Furthermore, the tracheids of the tensile parts outermost of bending specimen were subjected to the longitudinal tension and shear coupling stresses that led to the two kinds of cracks occurring, including trumpet-shaped cracks in the S2 layer, and S1/S2 interface debonding.