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Best Practices for Quasistatic Berkovich Nanoindentation of Wood Cell Walls

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Forest Biopolymers Science and Engineering, USDA Forest Service, Forest Products Laboratory, One Gifford Pinchot Drive, Madison, WI 53726, USA
2
Department of Materials Science and Engineering, University of Wisconsin—Madison, 1509 University Avenue, Madison, WI 53706, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Luis García Esteban
Forests 2021, 12(12), 1696; https://doi.org/10.3390/f12121696
Received: 2 November 2021 / Revised: 22 November 2021 / Accepted: 27 November 2021 / Published: 3 December 2021
(This article belongs to the Special Issue Nanoindentation in Wood)
For wood and forest products to reach their full potential as structural materials, experimental techniques are needed to measure mechanical properties across all length scales. Nanoindentation is uniquely suited to probe in situ mechanical properties of micrometer-scale features in forest products, such as individual wood cell wall layers and adhesive bondlines. However, wood science researchers most commonly employ traditional nanoindentation methods that were originally developed for testing hard, inorganic materials, such as metals and ceramics. These traditional methods assume that the tested specimen is rigidly supported, homogeneous, and semi-infinite. Large systematic errors may affect the results when these traditional methods are used to test complex polymeric materials, such as wood cell walls. Wood cell walls have a small, finite size, and nanoindentations can be affected by nearby edges. Wood cell walls are also not rigidly supported, and the cellular structure can flex under loading. Additionally, wood cell walls are softer and more prone to surface detection errors than harder inorganic materials. In this paper, nanoindentation methods for performing quasistatic Berkovich nanoindentations, the most commonly applied nanoindentation technique in forest products research, are presented specifically for making more accurate nanoindentation measurements in materials such as wood cell walls. The improved protocols employ multiload nanoindentations and an analysis algorithm to correct and detect errors associated with surface detection errors and structural compliances arising from edges and specimen-scale flexing. The algorithm also diagnoses other potential issues arising from dirty probes, nanoindenter performance or calibration issues, and displacement drift. The efficacy of the methods was demonstrated using nanoindentations in loblolly pine (Pinus taeda) S2 cell wall layers (S2) and compound corner middle lamellae (CCML). The nanoindentations spanned a large range of sizes. The results also provide new guidelines about the minimum size of nanoindentations needed to make reliable nanoindentation measurements in S2 and CCML. View Full-Text
Keywords: nanoindentation; wood; cell wall; elastic modulus; hardness nanoindentation; wood; cell wall; elastic modulus; hardness
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MDPI and ACS Style

Jakes, J.E.; Stone, D.S. Best Practices for Quasistatic Berkovich Nanoindentation of Wood Cell Walls. Forests 2021, 12, 1696. https://doi.org/10.3390/f12121696

AMA Style

Jakes JE, Stone DS. Best Practices for Quasistatic Berkovich Nanoindentation of Wood Cell Walls. Forests. 2021; 12(12):1696. https://doi.org/10.3390/f12121696

Chicago/Turabian Style

Jakes, Joseph E., and Donald S. Stone. 2021. "Best Practices for Quasistatic Berkovich Nanoindentation of Wood Cell Walls" Forests 12, no. 12: 1696. https://doi.org/10.3390/f12121696

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