Micro- and Nano-Scales Three-Dimensional Characterisation of Softwood

Abstract

Understanding the mechanical response of cellular biological materials to environmental stimuli is of fundamental importance from an engineering perspective in composites. To provide a deep understanding of their behaviour, an exhaustive analytical and experimental protocol is required. Attention is focused on softwood but the approach can be applied to a range of cellular materials. This work presents a new non-invasive multi-scale approach for the investigation of the hygro-mechanical behaviour of softwood. At the TOMCAT beamline of the Paul Scherrer Institute, in Switzerland, the swelling behaviour of softwood was probed at the cellular and sub-cellular scales by means of 3D high-resolution phase-contrast X-ray imaging. At the cellular scale, new findings in the anisotropic and reversible swelling behaviour of softwood and in the origin of swelling hysteresis of porous materials are explained from a mechanical perspective. However, the mechanical and moisture properties of wood highly depend on sub-cellular features of the wood cell wall, such as bordered pits, yielding local deformations during a full hygroscopic loading protocol.

Multiscale Mechanical Performance of Wood: From Nano- to Macro-Scale across Structure Hierarchy and Size Effects

“…As follows from Table 4 , the strength of cellulose nanocrystals, assessed both by calculations and by experimental techniques, is 4.9–10 GPa, while the strength of nanofibrils with a diameter 3–15 nm is close to the lower end of this range [ 5 , 40 , 65 , 66 , 67 , 68 ]. These values exceed the strength of cellulose microfibers 8–12 µm in diameter, which is 0.5–1.65 GPa, by about one order of magnitude [ 5 , 40 , 66 , 104 , 106 , 107 ]. The typical nanohardness values H NI for cell walls with a thickness of 2–5 µm are about 0.3–0.5 GPa [ 70 , 71 , 72 , 73 , 74 , 75 , 107 , 108 , 109 , 110 ], which is 2–3 times less than the strength of cellulose microfibers.…”

“…Nano- and micro-structures of cellulose materials and their properties strongly depend upon the specifics of interaction between nanocrystals in elementary fibrils and the ordering and binding of the latter in nano- and micro-fibers [ 103 , 104 , 105 , 106 , 107 ]. Mechanical, strength in particular, properties of cellulose nano- and micro-structures are structure sensitive, just as those of most other other organic and non-organic materials.…”

“…Results obtained using AFM and NI are in agreement with each other regarding the measurement accuracy, despite using different probes and measurement techniques, so that they are just as reliable as the ones obtained using the undebatable method of uniaxial tension. Usually, its tensile strength is two to three times higher than compression strength or hardness [ 5 , 40 , 104 , 106 , 107 ], unlike void-free materials, where the reversed value is quite typical. For example, the Tabor ratio for metals is well known, where hardness is three times higher than the yield stress.…”

A versatile laboratory setup for high resolution X-ray phase contrast tomography and scintillator characterization

“…This makes it an attractive technique whenever the integrity of the sample is crucial, as e.g. in bio-medical imaging [11,23,28,35,45], archaeometry [38,40], paleontology [13], industrial quality control [7,33], and material science [14,42].…”

X-ray Digital Radiography and Computed Tomography

“…Further topics covered in this Special Issue include the use of synchrotron light for phase-contrast and multi-contrast imaging [ 8 , 9 , 10 , 11 ] and analytical techniques, such as microscopic synchrotron X-ray fluorescence [ 12 ]. Several contributions deal with new performing algorithms developed for the suppression of cone-beam artifacts in CT images [ 13 ] and signal retrieval from non-sinusoidal intensity modulations in X-ray and neutron interferometry [ 14 ], or devoted to innovative techniques, such as multiscale holotomography [ 15 ], rotation-free dynamic multi-angle X-ray tomography [ 16 ] and high-speed X-ray imaging [ 17 ].…”