Mechanical properties of interfaces within a flax bundle—Part II: Numerical analysis

In the experimental part of this study, mechanical tests and microscopic observations were performed on pairs of flax fibres to characterize the middle lamella at the interface between the two fibres. The main objective of this second part has been to study numerically the tensile strength of the bundles, taking into account the mechanical behaviour of the middle lamella. The bundle geometry was reconstructed on the basis of optical micrographs, and used a staggered longitudinal arrangement of the fibres. A bilinear cohesive zone model was used to describe the mechanical behaviour of the middle lamella. A first model with a pair of fibres was developed in order to calibrate the main parameters of the non-linear algorithm and to validate the scale-up law used. Then a second model, representing a bundle of seven fibres, was developed to analyse the tensile strength of the bundle when the gauge length varies. Numerical simulations were carried out using appropriate contact elements of ANSYS to model the interface behaviour. Comparisons between numerical results and experimental values show good agreement and prove the relevance of this study.