Applying a Full-Field Measurement Technique to Characterize the Mechanical Response of a Sunflower-Based Biocomposite

This work is part of a project aimed at developing a new biocomposite material that can be used for thermal insulation purposes. This material is mainly composed of sunflower stem chips. A chitosan-based biomatrix is used as binder between them. We focus here only on the mechanical response of this biocomposite. The goal is to investigate experimentally the link between its macroscopic response and phenomena which occur at the scale of the constituents, namely the bark and pith chips. The grid method, which is one of the full-field measurement systems employed in experimental mechanics to measure displacement and strain fields, is employed because of the very heterogeneous nature of this material. This heterogeneity is not only due to the contrast in rigidity between bark and pith, but also to the presence of voids within the material. These voids, as well as the presence of pith, lead us to develop and employ a specific marking procedure for the specimen surface under investigation. Two values for the mass percent fraction of chitosan are investigated, to observe the influence of this parameter on the global stiffness of the material and on local phenomena that occur in its bulk. The full-field measurement technique employed here leads us to detect and quantify significant heterogeneities in the strain fields, which are closely related to the material heterogeneities themselves.