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Mechanical responses of Chrysopogon zizanioides roots under cyclic loading conditions

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A Correction to this article was published on 28 October 2023

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Abstract

Background and aims

Data on cyclic root mechanical behaviour (i.e. roots subjected to repeated loading and unloading cycles at a given frequency) are lacking. In this study, cyclic root mechanical traits were measured.

Methods

Chrysopogon zizanioides L. roots were sampled for monotonic and cyclic tensile tests. The effects of pre-cyclic loading on the monotonic mechanical properties (n = 92) and reversal strains on any changes in cyclic mechanical properties (n = 88) were measured. The root water content and root traits, including diameter, dry density, and specific root length (SRL), were also measured for each sample.

Results

Pre-cyclic loading at 5% and 50% strain levels reduced the root tensile strength (Tr) by 18.17% and 27.10%, respectively, yet increased the breakage strain (εr) by 30.85% and 52.13%, respectively. Although Tr and the Young’s modulus (E) were reduced after cyclic loading, the trend of their correlations with root diameter (i.e. negative power law correlation) was unaffected. Remarkable hysteresis was found in any loading cycle. The hysteresis loop size and peak tensile stress decreased abruptly during the first 20 cycles. The peak tensile stress explained more than 86% of the variability of Young’s modulus along the unloading path at all the reversal strains.

Conclusion

The root mechanical traits obtained from monotonic tests should not be used to explain the root reinforcement in cyclic events because of cyclic-induced changes in the Tr and E. Regardless of the strain range experienced in a cyclic event, determining the changes in root mechanical properties during the first 20 regular cycles of loading is crucial.

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Data availability

The data that supports the findings of this study are available from the first and corresponding authors upon reasonable request.

Change history

Abbreviations

\(d\) (mm):

Root diameter

\(e\) (mm∙mm−1):

Root elongation at breakage

\(f\) (Hz):

Loading frequency

\(l\) (mm):

Root gauge length

\({l}_{t}\) (mm):

Total length of the root sample

\({m}_{a}\) (g):

Weight of root sample before testing

\({m}_{d}\) (g):

Root dry weight

\({m}_{f}\) (g):

Weight of root sample after testing

\(v\) (mm∙mm−1):

Loading/unloading rate

\({v}_{d}\) (mm−3):

Root dry volume

\(w\) (g∙g−1):

Root water content

\({A}_{i}\) (Pa∙m):

Area of hysteresis loop at ith cycle

\(E\) (MPa):

Young’s modulus

\({E}_{r}\) (MPa):

Modulus after being loaded of 50 cycles

\({E}_{load}\) (MPa):

Young’s modulus of loading cycle

\({E}_{load,i}\) (MPa):

Young’s modulus of ith loading cycle

\({E}_{unload}\) (MPa):

Young’s modulus of unloading cycle

\({E}_{unload,i}\) (MPa):

Young’s modulus of ith loading cycle

\(F\) (N):

Tensile force

\(SRL\) (m∙g−1):

Specific root length

\({T}_{p}\) (MPa):

Peak tensile stress

\({T}_{pi}\) (MPa):

Peak tensile stress at ith cycle

\({T}_{r}\) (MPa):

Tensile strength

\(\varDelta A\) (MPa):

Difference in the area of hysteresis loop between the first and 50th cycles

\({\varDelta E}_{load}\) (MPa):

Difference in Young’s modulus along the loading cycle between the first and 50th cycles

\({\varDelta E}_{load}\) (MPa):

Difference in Young’s modulus along the unloading cycle between the first and 50the cycles

\({\varDelta T}_{p}\) (MPa):

Difference in peak tensile stress between the first and 50th cycles

\({\varepsilon }_{b}\) (mm∙mm−1):

Root estimated root breakage strain

\({\varepsilon }_{r}\) (mm∙mm−1):

Root breakage strain

\({\rho }_{d}\) (g∙mm−3):

Root dry density

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Acknowledgements

The authors gratefully acknowledge the grants provided by the Hong Kong Research Grant Council (GRF/16202720, CRF/C6006-20G and N_HKUST603/22) and the National Natural Science Foundation of China (NSFC) (grant no. 51922112). The third author (David Boldrin) acknowledges the financial support by the EPSRC project (EP/R005834/1) “Climate Adaptation Control Technologies for Urban Spaces (CACTUS)” and The James Hutton Institute, which receives funding from the Rural & Environment Science & Analytical Services Division of the Scottish Government.

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Authors and Affiliations

  1. Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Hong Kong, SAR, China

    Zhaoyi Wu & Anthony Kwan Leung

  2. The James Hutton Institute, Invergowrie, Dundee, UK

    David Boldrin

  3. School of Science and Engineering, University of Dundee, Dundee, DD1 4HN, UK

    David Boldrin

Authors
  1. Zhaoyi Wu
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  2. Anthony Kwan Leung
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  3. David Boldrin
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Contributions

AL and DB conceived the research idea. ZW designed and conducted the experiments and produced the first draft of the paper. AL contributed to writing the paper. DB commented the paper.

Corresponding author

Correspondence to Anthony Kwan Leung.

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Conflict of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Responsible Editor: Zhun Mao.

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Wu, Z., Leung, A.K. & Boldrin, D. Mechanical responses of Chrysopogon zizanioides roots under cyclic loading conditions. Plant Soil 494, 437–459 (2024). https://doi.org/10.1007/s11104-023-06289-9

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