Damage Kinetics at the Sub-micrometric Scale in Bast Fibers Using Finite Element Simulation and High-Resolution X-Ray Micro-Tomography

Abstract

This study combines experimental testing and computation analysis to reveal the role of defects and sub-micrometric microstructure in tensile behavior of hemp bast fibers. In particular, these structural defects represent the footprint of the processes to which the fibers elements are subject along the whole transformation chain from the plant to the end use product. Tensile experiments performed on elementary fibers and bundles in a wide diameter range (40–200 μm) are simultaneously conducted with X-ray micro-tomography observation. 3D images of ultra-fine resolution (voxel size of 280 nm) are achieved at different deformation magnitudes up to the complete failure thanks to the use of synchrotron radiation (ESRF, Grenoble, France). A Finite element (FE) model is implemented based on the conversion of the tomograms into 3D meshes. High performance computing is used to simulate the tensile response of the hemp bast fibers. In particular, the effects of notching and sub-micrometric structure of the fibers are explored. Results show the presence of different types of diffuse damage kinetics, which are related to the variability in the fiber size, surface defects and the presence of the lumen space. The damage behavior is found to be sensitive to the type of stress criterion implemented in the FE computation. The predictive analysis demonstrates the relevance of using embedded microstructure simulations to reveal the extent of stress localization and predict the failure properties in bast fibers for innovative composite manufacturing for instance.

A critical review of the ultrastructure, mechanics and modelling of flax fibres and their defects

“…A drawback of the study is that the fibre cross-section is assumed to be circular even though it is not, and the elasto-plastic constitutive law implemented for hemicellulose is better suited for metals. Further modelling developed by Guessasma et al [110] revealed that delaminated areas, weakly…”

“…In the present review, we present a broader definition, dividing defects into two types: material discontinuity and the presence of inhomogeneity. Surface and bulk categories can further distinguish defects depending on their localization [110]. Surface discontinuities refer mainly to impurities or surface microcracks [111], whereas bulk discontinuities include cracks and interlaminar decohesion.…”

Beating of hemp bast fibres: an examination of a hydro-mechanical treatment on chemical, structural, and nanomechanical property evolutions

“…The mechanical properties of the cell walls are governed by several factors, such as the microfibrillar angle (Burgert and Keplinger 2013), the chemical composition (Lefeuvre et al 2014), the crystallinity, the defect density (Andersons et al 2009; Beaugrand and Guessasma 2015; Gourier et al 2017;Hughes 2012;Guessasma and Beaugrand 2019) and the mesoporosity (pore size between 2 and 50 nm), even if the last factor is not yet well established at the elementary fibre scale. Arnould et al (2017) mapped the stiffness of the cell wall of green flax stems by atomic force microscopy revealing a gradient in mechanical properties along the cross section at nanoscale.…”

Novel Insight into the Intricate Shape of Flax Fibre Lumen

“…In addition, small internal cavities with diameters of a few µm were also reported as contributors to the porous structure of plant fibres [3][4][5]. This distinctive characteristic can be involved in the generation of stress concentrations, leading to the failure of the fibre [3,6,7]. Moreover, porosities in plant fibres are also the location of free water filling at high moisture content.…”