Multiscale characterization and micromechanical modeling of crop stem materials

Abstract

An essential prerequisite for the efficient biomechanical tailoring of crops is to accurately relate mechanical behavior to compositional and morphological properties across different length scales. In this article, we develop a multiscale approach to predict macroscale stiffness and strength properties of crop stem materials from their hierarchical microstructure. We first discuss the experimental multiscale characterization based on microimaging (micro-CT, light microscopy, transmission electron microscopy) and chemical analysis, with a particular focus on oat stems. We then derive in detail a general micromechanics-based model of macroscale stiffness and strength. We specify our model for oats and validate it against a series of bending experiments that we conducted with oat stem samples. In the context of biomechanical tailoring, we demonstrate that our model can predict the effects of genetic modifications of microscale composition and morphology on macroscale mechanical properties of thale cress that is available in the literature.

Thermodynamically consistent concurrent material and structure optimization of elastoplastic multiphase hierarchical systems

“…The first part of this equation directly comes from the incremental form of the principle of maximum plastic dissipation outlined in (41). Similarly, the second part is the incremental form of the Helmholtz free energy rate defined in (31).…”

“…including all constraints defined through the stress admissible set E Σ n+1 and microscale design admissible set E ad . The first two conditions are essentially the elastoplastic constitutive equations relating the macroscale stress with the macroscale strains via (39) and the constraint on the macroscale stress defined through the homogenized yield criterion (41). The third condition is the definition of the Helmholtz free energy in terms of microscale design variable m x,j n+1 .…”

“…This drawback limits existing approaches to small two-scales problems, even in the simplest case of hierarchical materials with linear elastic constituents. Continuum micromechanics provides a rigorous framework to derive analytical estimates of macroscale elastoplastic properties [37][38][39] and has been successfully applied to describe many multiphase hierarchical systems such as plant, wood, bone, and cementitious materials [40][41][42][43][44][45]. In the context of concurrent material and structure optimization, we recently integrated continuum micromechanics based homogenized estimates in end-compliance optimization problems, which rendered our framework computationally tractable for multiphase hierarchical systems with several material length scales [46].…”

Micro-CT Imaging of Low-density Plant Stems

“…Small grain cereals lose a high percentage of their yield through lodging (buckling of the stems near ground level) before harvesting due to the weak structure of the stem, especially under heavy rain and wind (1). Computational models are being used to simulate stem collapse under loads to better understand the relationship between the stem's structure and its strength (2). With this understanding, the stem's structure can then be modi ed through conventional breeding or genetic engineering to increase its resistance against lodging.…”

Concurrent material and structure optimization of multiphase hierarchical systems within a continuum micromechanics framework

“…Continuum micromechanics-based homogenization has been successfully applied to describe natural multiscale systems such as wood, bone, or cement (Fritsch and Hellmich 2007;Fritsch et al 2009;Pichler and Hellmich 2011;Morin et al 2017;Hofstetter et al 2005). In our recent work (Gangwar and Schillinger 2019;Gangwar et al 2020), we showed that continuum micromechanics models can accurately predict both linear elastic and inelastic behavior of plant materials. We also demonstrated that each hierarchical level can be statistically characterized through microimaging techniques.…”