A 3-D finite element analysis of the sunflower (Helianthus annum L.) fruit under impact: a useful approach for the understanding and improvement of its hullability

摘要

Before oil extraction sunflower seeds are hulled, i.e. the pericarp (hull) is separated from the seed by mechanical impact. Hullability (H), defines how easily the hull can break and set apart from the seed and has a direct effect on the industrial oil extraction performance. H mainly depends on the fruit's morphology and hull's biomechanical properties. The study of hulls showing histological differences could be useful to infer its best distribution of tissues and to define, for breeding purposes, the best hull architecture for industrial processing. Using a numerical approach we have been able to calculate and visualize the pattern of stresses produced in the 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. Using a non-linear FE commercial code, It was seen that the points of contact between those tissues, with different mechanical properties, and the hull's longitudinal parenchymatous rays were more likely to mechanically fail. The simulated patterns of failure closely agree with those observed after subjecting fruits to compressive loads. The procedure described here can be considered the first step of a protocol of analysis leading to a genetic improvement of H and could be useful to quantify and qualify, under different hull structural parameters, the distribution and magnitude of the stresses generated in the pericarp during the mechanical hulling.