Failure mechanisms and bending strength of Fuchsia magellanica var. gracilis 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.

Trellis-forming stems of a tropical liana Condylocarpon guianense (Apocynaceae): A plant-made safety net constructed by simple “start-stop” development

“…It was found that young shoots and more mature shoots of wild-type Manihot esculenta showed ductile failure of the stem under three-point bending loads than more catastrophic brittle failure ( Ménard et al., 2013 ). Future studies might explore how initial growth of TYPE II wood influences toughness and the type of failure in climbing stems as has been done for shrubs and trees ( Ennos and van Casteren, 2010 ; van Casteren et al., 2012 ; Hone et al., 2021 ). Downward deflection of the stem and presence of large leaf areas is probably an important function in the formation of trellises where more searcher stems do not find a support than find them.…”

Fracture and repair in a bio‐inspired self‐healing structure

“…Examples are structural beams in buildings, bicycle frames, and antennae. Previously, 17 we investigated the failure modes in stems of the shrub Fuchsia magellanica, which are partially woody, having a relatively stiff outer cortex containing dead, lignified cells and a softer inner core containing living cells. Vascular channels run longitudinally.…”

“…It is envisaged that, ultimately, this structure will be made in the form of a much longer cylinder, suitable for F I G U R E 2 Results from previous work on bending of plant stems. 17 incorporation into a system where it will be subjected to bending such as cantilever bending or three-point bending. However, we were limited in the length of our specimens by the 3D printing equipment available to us, and by the method we used to incorporate the healing agents.…”

“…Since we had already identified that the initial damage will be internal cracking due to ovalization, 17 we simulated this by creating ovalization in a simple way, applying compression across the diameter, as shown in Figure 3. The similarity between ovalization caused by bending and ovalization due to diametral compression has been recognized and used in previous work.…”

Study on the Shear and Bending Mechanical Properties of Millet Stem

“…The mechanical parameters of the stems provide a reference for the mechanized production of crops [4]; plant stems have a complex structure and are capable of resisting various types of loads [5], and test methods are used to obtain the parameters include compression [6], shearing [7], bending [8], and tensile [9] tests. The mechanical strength of the stem is affected by factors such as stem size, moisture content, internode position, and loading rate, each to varying extents [10][11][12][13][14][15].…”