A 3-D finite element analysis of the sunflower (Helianthus annuus L.) fruit. Biomechanical approach for the improvement of its hullability

For the sunflower fruits, hullability (H) is a technical parameter that defines how easily the hull can be broken and set apart from the kernel. H mainly depends on the morphology of the fruit and the biochemical properties of the hull. Finite element analysis (FEA) was used to model the mechanical behavior of the sunflower fruit hull after the fruit impact. A 3-D model of an entire fruit was designed in terms of strain incompatibilities between two different tissues, parenchyma and sclerenchyma. Impact was simulated for three orientations of the fruit: longitudinal, transversal and lateral; and for two thicknesses of the hull: 100 μm and 300 μm. The validation of the FEA model was made based on a comparison of theoretical calculations and experimental data. It was noticed that the points of contact between the above mentioned tissues – with different mechanical properties – and the longitudinal parenchymatous rays of the hull were the main structural sites prone to fail mechanically after impact.The simulated patterns of failure closely agree with those observed after subjecting fruits to compressive loading. The procedure described in this work could be useful to quantify and qualify, under different hull structural parameters, the distribution and magnitude of stresses generated in the hull during industrial mechanical hulling. It can be considered the first step of a protocol of analysis leading to a genetic improvement of H.