Timothy Hone (1), Max Mylo (2,3), Olga Speck (2,3), Thomas Speck (2,3), David Taylor (1)
Journal of the Royal Society Interface, 18, Issue 175, February 2021. DOI: 10.1098/rsif.2020.1023

Keywords

greenstick fracture; plastic hinge; bending; cracking; transverse stress; plant stems

Abstract

In the course of biological evolution, plant stems have evolved mechanical properties and an internal structure that makes them resistant to various types of failure. The mechanisms involved during damage development and failure in bending are complex and incompletely understood. The work presented builds on a theoretical framework outlined by Ennos and van Casteren, who applied engineering mechanics theory to explain why different woody stems fail in different ways. Our work has extended this approach, applying it to a detailed analysis of one particular species: Fuchsia magellanica var. gracilis. When subjected to three-point bending, stems of this species exhibited one of two failure mechanisms: a plastic hinge or a greenstick fracture. We developed a predictive model using a computer simulation and a mathematical analysis using the theory of plastic bending. Required material properties were obtained from tests, the literature and imaging techniques. We found that greenstick fractures are more likely to occur in more lignified stems with a higher density. We discovered a new failure mode: an internal crack caused by tensile transverse stress. This work helps in understanding how plants have evolved their bending resistance and may assist in the creation of novel engineering structures inspired by these principles.

How Our Software Was Used

Dragonfly was used for the 3D reconstruction and rendering of Micro-CT scans.

Author Affiliation

(1) Trinity Centre for Biomedical Engineering, Department of Mechanical and Manufacturing Engineering, Trinity College Dublin, The University of Dublin, Ireland.
(2) Plant Biomechanics Group, Botanic Garden, Faculty of Biology, University of Freiburg, Germany.
(3)Cluster of Excellence livMatS @ FIT—Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Germany.