Biomimetic Research for Folding and Unfolding Manners of Leaves and Flowers on Plants

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One of the research in this project is to reveal the unfolding manner of regularly corrugated simple leaves paying attention to the difference between leaf shapes during unfolding of hornbeam and common alder, i.e.a relatively flat shape in hornbeam and a V-shape in common alder leaves. From the optical observation of their leaves and the unfolding simulation using numerical models and vector analysis, it was found that the crease interval ratio(a^*)larger than 1, which is a^*【approximately equal】1.4 in common alder leaves, causes the V-shape unfolding.The second research is to investigate of the unfolding manner of maple leaves which have a fan-type bellows pattern. Based on the measurements, a number of numerical leaf unfolding models were constructed to simulate the fan-type unfolding like maple leaves. The locations of the leaf elements and the creases during unfolding were obtained by vector analysis. From the measurements and observations, it was found that there are small angular gaps of 1°〜2° between the veins when the leaf is fully folded. This may be for avoiding an increase in local volume due to the overlapping of relatively thick veins. These small angular gaps are quite advantageous to compact folding.In order to examine the unfolding manner of rolled leaves, we took butterbur leaves as a target to research. As the first step, the configuration of butterbur leaves, e.g.the angle between veins and the thickness of lamina, was measured using optical devices. It was found that butterbur leaves have veins with an ellipse cross-section instead of a circle cross-section and analopgous geometry irrespective of their size. By using the geometrical data and mechanical properties of veins and a lamina, a number of leaf models were made for FEM analysis. It was found that the capability for supporting load of the leaf model with the most similar venation pattern to a real butterbur leaf was greater than that of other models with simplified patterns.