EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The connection of different parts with varying geometries is a challenge both in engineering and in nature. A particularly demanding case is the connection of rod-shaped and planar structures. Many technical approaches so far rely a on large number of individual components and are often prone to failure due to areas of high stress and strain occurring between the individual parts. A successful implementation of such a connection, without these pitfalls, can be found in nature in the foliage leaves of plants. In these leaves rod-shaped stalks and planar blades are connected by smooth and robust transition zones. There exist different types of transition zones in foliage leaves, depending on the spatial arrangement of stalk and blade, as well as the plant's body plan, which affects the internal arrangement of the strengthening elements in the leaves. In order to study similarities and differences of various transition zones found in foliage leaves of plants, we selected four leaf models, which differ in the spatial configuration of blade and stalk (3D-configuration: peltate leaves and 2D-configuration: stalk connected to the basal region of the blade) and in the 3D-arrangement of the involved tissues (body plan of monocotyledons and dicotyledons). The investigations included a quantitative analysis of the internal tissue arrangements using serial thin-sections and µCT scans, as well as a quantitative description of size, geometry and shape of the transition zones. We found that the gradients of all these parameters overlap and integrate with each other, where some features depend more on the body plan and others more on the spatial configuration. Overall, the insights gained from the four selected transition zones can be considered a template for the design and optimisation of more robust and diverse technical transition zones between rod-shaped and planar structures.