Amazonian palms as underestimated crops: Elastic properties of leaflets revealed by digital image correlation combined with tensile testing

Abstract

Understanding the mechanical behaviour of plant fibres is crucial not only for advancing knowledge of plant biomechanics but also for exploring their potential in bio-based material applications. Amazonian palms, in particular, represent highly valuable but underestimated crops. Tensile tests are widely used to characterize the mechanical properties of biological materials, such as different plant organs. However, assessing their elastic properties from coupons requires accurate strain measurements, which remain challenging for such heterogeneous materials, thereby driving the development of advanced measurement techniques. This study focuses on the analysis of strain measurements using Digital Image Correlation (DIC), a non-contact optical technique that evaluates displacement fields from images captured during mechanical tests. Digital image correlation offers several advantages, including high spatial resolution, two-dimensional mapping of local strains, and non-intrusive measurement, while presenting challenges such as proper coupon positioning, image processing, accurate error quantification, and the assessment of experimental biases (e.g., offsets caused by edge curvature). This study evaluates the potential of DIC in assessing the tensile behaviour of leaflets of two Amazonian palm species (Euterpe oleracea and Oenocarpus bataua), in comparison to laser extensometry. Repeated tensile tests allowed the estimation of the accuracy of DIC and its reliability for measuring strains, elastic moduli and Poisson’s ratios. The analysis revealed significant differences in elastic moduli and Poisson’s ratio between the two palm species, and spatial heterogeneity of full-field deformation within the leaflet coupons. Careful identification and exclusion of local artefacts were applied to obtain reliable measurements and ensure meaningful comparisons between the leaflets of the two studied species. Overall, these results confirm the potential of 2D-DIC for the mechanical analysis of plant materials, while also opening perspectives in understanding the relationships between anatomical structure of leaflets and their mechanical properties.