Principles of Branching Morphology and Anatomy in Arborescent Monocotyledons and Columnar Cacti as Concept Generators for Branched Fiber‐Reinforced Composites

Abstract

The branching of arborescent (tree‐like) monocotyledonous plants of the genus Dracaena or of columnar cacti differ considerably from that observed in other dicotyledonous or gymnosperm trees. The investigated ramifications exhibit distinctive morphological and anatomical features. In arborescent monocotyledons the side branches are attached to the main stem by a fiber‐reinforced tissue newly formed during secondary growth, clasping the main stem and finally resulting in a “flange‐mounted” structure. In the case of columnar cacti the most obvious feature is the pronounced constriction at the attachment point of the branches that is also mirrored in the lignified vascular tissue. One might argue that these characteristic morphological and anatomical features in regions exposed to high mechanical stresses represent structural weaknesses. However, the outer shape and the inner structures of the ramifications cause considerable stability and structural integrity of the stem‐branch connection under static and dynamic loading. Our results allow concluding that load‐adaptation in ramified plant structures is a result of a combination of optimization in outer shape and fiber arrangement within the ramifications. Numerical methods simulating the mechanical behavior based on data obtained from the studied plants support this assumption. A deeper understanding of the outer shape of the connection between shoot and branch as well as of the arrangement of the lignified vascular tissues in the branching region, may contribute toward alternative concepts for branched technical light‐weight‐structures. In particular for braided fiber‐reinforced composites this biomimetic approach might help to keep the demand on the available design space as small as possible.

Biomechanics of selected arborescent and shrubby monocotyledons

“…They also confirm the status of these plants as interesting concept generators for the development of branched and unbranched fibre-reinforced materials and structures with enhanced properties [6,47–49]. The axes of these plants consist of materials that combine low density with sufficient mechanical stiffness, which result in lightweight structures with optimized structural density–stiffness gradients.…”

“…In addition, these data can be incorporated in finite element models at cell and tissue level that mirror the anisotropy and the stress–strain behaviour of the investigated plants at stem level [6–7]. This allows for a deepened understanding of the structural and mechanical requirements of Dracaena marginata , which was chosen as a representative model organism for arborescent monocotyledonous plants with lignified vascular bundles and anomalous secondary growth.…”

Biomimetic fiber‐reinforced composite structures based on natural plant ramifications serving as models

“…The biomechanical understanding of the three‐dimensional fiber arrangement allows for developing novel biomimetic nodal elements for different applications in aircraft and automotive construction, in prosthetics and sports equipment or, most recently, in civil engineering and architecture. In contrast to earlier stand‐alone projects, our integrated approach focuses not only on the mechanical analysis of the biological models; it even comprises the downstream technical implementation with suitable production processes such as the (semi‐)automated braiding technique .…”

Biomimetic Fiber-Reinforced Compound Materials

“…The structural analysis and the mechanical tests are complemented by FE-analyses ( Fig. 28A) Schwager et al, 2010). Fig.…”

“…In plants, branchings are developed and shaped in a manner so that notch stresses present in 'joints' (i.e. stem-branch attachments) are diverted and distributed, so that similar zones of weakness do not develop (Mattheck, 1990(Mattheck, , 2007Mattheck & Tesari 2002;Schwager et al, 2010). Generally speaking, plants are ‚ideal' concept generators for improving branched or unbranched technical structures since: -Plants typically 'avoid' critical notch stresses -Plants are lightweight structures -Plants possess interesting mechanical properties like for example high stiffness and strength combined with a benign fracture behavior and good damping -The laminated configuration of technical fiber-reinforced compound materials and the structure of some plant stems are highly comparable (Fig.…”