Koh R.; Madsen B.; 2018, Strength failure criteria analysis for a flax fibre reinforced composite.                                                                                                                                                 Abstract: Natural fibre composites are being utilized increasingly in high-performance, structurally demanding applications,in part because of their material properties and in part because they are a more sustainable choice compared to other engineering materials. However, there is a current lack in understanding of best practices for strength modelling of natural fibre composites. This study aims to understand how well common failure criteria predict strength in multi-directional flax fibre composite laminates. Four failure criteria are compared to experimental data from tension and compression tests of flax composite laminates with five different layups. Parametric optimization is performed on each criterion in order to determine the optimal strength, stiffness, and interaction parameters. In conclusion, the Hashin and Puck failure theories are recommended because they have the smallest error compared to experimental data. Values for parallel-to-fibre shear strength are also presented, and they are found to be comparable to the shear strength of conventional glass fibre composites with similar matrix materials.

Koh R.; Clouston P.; 2017, In-plane shear properties of laminated wood from tension and compression tests of angle-ply laminates.                                                                                     Abstract: Experimental methods for the characterization of shear strength and stiffness of both wood-based and glass-based or carbon-based composite materials are highly contested because shear properties are difficult to isolate experimentally. A comprehensive literature review on the subject is presented, considering methods for both structural composite lumber and traditional composite laminates. The researchers present a novel method for calculating shear strength, stiffness, and interaction parameters of laminated wood-veneer panels by coupling experimental data from tension and compression tests of multiaxial laminates with an optimization routine for two failure criteria theories from the literature. Optimal shear parameters are reported for both theories.