TutorialExperimental study and numerical simulation on the structural and mechanical properties of Typha leaves through multimodal microscopy approaches
Graphical abstract
Typha leaf is an ideal bionic prototype utilized for lightweight design. In this paper, the structure and mechanical properties of leaves were investigated under Micro-CT, SEM, mechanical tests and simulation analysis. The results showed that the internal rib structure of Typha leaf effectively enhances the resistance to compression and bending deformation.
Introduction
Typha glauca, also named water candle, usually grows in shallow water marshes as marsh perennial herbaceous plants. Typha plants are widely used in constructing wetlands for the ecological restoration (Mburu et al., 2014, Meng et al., 2016, Pandey et al., 2014) and sewage treatment (Anisuzzaman et al., 2015, Bonanno and Cirelli, 2017, Ciria et al., 2005, Lawrence et al., 2017, Salem et al., 2017). They are important raw materials for heat preservation (Dieye et al., 2017, Luamkanchanaphan et al., 2012), composite panels (Bajwa et al., 2015, Wuzella et al., 2011), weave and paper (Jahan et al., 2007) due to its fiber length, toughness and heat preservation performance. More importantly, as a lightweight thin-walled beam with impressive length and a large slenderness ratio, Typha leaf could bear their large self-weight and greater loadings imposed by wind. It has attracted more and more attention of many scholars that how Typha leaves achieve high-intensity characteristics under lightweight conditions.
Through natural selection, Typha leaf has evolved optimal chiral morphology in the height direction. In order to understand the influence of chirality on mechanical behavior of Typha leaf, the chiral morphology and the wind adaptation of Typha leaves were widely investigated. Zhao et al., 2015a, Zhao et al., 2015b, Zhao et al., 2016 reported the biomechanical strategies, aeroelastic behavior and synergistic effect of chiral morphology and reconfiguration in cattail plants in wind by fluid dynamics simulations and experimental measurements. It is found that the chirality-dependent flutter, including wind-induced rotation and torsion, is a crucial strategy for leaves to accommodate wind forces, and the twisting chirality of Typha leaf can significantly improve their survivability against failure under both internal and external loads.
The macro and micro structure of Typha leaves also has a strong influence on their mechanical properties. For instance, the Typha leaf has the structure of sandwich type and the structure allows leaves to have a large surface area for photosynthesis while providing sufficient structural rigidity and strength at relatively low mass to maintain their more or less upright position in the living plant (Gibson, 2005, Rowlatt and Morshead, 1992).
In addition, Allan Witztum and Randy Wayne (Witztum and Wayne, 2014, Witztum and Wayne, 2015, Witztum and Wayne, 2016) studied the structure and mechanical properties of the fiber cables within the leaf. It is found that the measured stiffness and tensile strength of the non-lignified fiber cables in the air-filled lacunae of leaf blades were in the gigapascal range, and the fiber cables are strong under tension probably serve to protect the flexible leaves from buckling during high winds. Lately, the tensile and bending performance of Typha leaf were examined and the results showed that the mechanical properties of leaves significantly decrease along its height direction, and both of the parenchyma walls and foam tissues could effectively improve the stability of the plants to against bending failure (Zhao et al., 2015a, Zhao et al., 2015b).
Although the aforementioned works have investigated the mechanical behavior of the Typha leaf from varied viewpoint, there were still some unexplored aspects about the relationship between structure and mechanics, such as the axial compression properties, the mechanical deformation behaviors and the influence of internal structure on the mechanical properties of the leaf blade. In this paper, the structure and mechanical properties of Typha leaf was studied and the effect of internal structure on the mechanical properties was also discussed. Firstly, Micro-CT and SEM were performed to observe the macroscopic and microscopic structure characterization of Typha leaf and the structure parameters of the leaf were extracted by the image processing software Digimizer. Secondly, axial compression, lateral bending and uniaxial tension tests were performed to examine their mechanical behavior by the universal testing machine. Thirdly, inspired by the sandwich structure in Typha leaf, three models were created to verify the effect of internal structure on the mechanical properties using the nonlinear finite element code LS-DYNA.
Section snippets
Materials
The fresh and mature Typha leaves used in this study were collected in random from Nanhu park in Changchun, China. All sampled leaves were fully developed without any visual damage or senescence. The samples were wrapped in preservative films and stored at 4 °C to avoid loss of turgor pressure before the observation and mechanical measurements. Observations and measurements were performed not more than three days after the collection.
Structure feature extraction of Typha leaves
The three-dimensional macroscopic morphology of the Typha
Macroscopic morphology analysis of the Typha leaf
The Typha leaf was studied and synchrotron radiation CT images of a small section in the middle of the leaf are shown in Fig. 1(a)–(c). In Fig. 1(b), the 3D structure of the leaf shows that the Typha is constituted by epidermis, diaphragm and partition, which resembles a sandwich structure with two stiff strong faces separated by a lightweight core. According to the results from the CT analysis, the porosity of this small sample is up to 96%.
Fig. 1(c) illustrates three basic orthographic views
Conclusions
In this study, the structure and mechanical properties of Typha leaf were investigated under Micro-CT, SEM and some mechanical testing machines. Then its macrostructure and microstructure characteristics of leaf were selected to establish three models. The effect of internal structure on the mechanical properties was studied by using the nonlinear finite element code LS-DYNA. According to the microstructure, mechanical tests and numerical results, it can be found that the structure of Typha
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No.51375006, 51405186 and 51675223), Postdoctoral Science Foundation of China (No. 801161050414 and 2016M590256) and the Technology Development of Jilin Province (No. 20150520106JH).
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