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. 2023 Apr 18;13(1):6348.
doi: 10.1038/s41598-023-33054-w.

Characterisation of thermally treated beech and birch by means of quasi-static tests and ultrasonic waves

Hajir Al-Musawi  1 , Elisa Manni  2   3 , Alexander Stadlmann  4 , Bernhard Ungerer  2 , Mojtaba Hassan Vand  5 , Olaf Lahayne  6 , Riccardo Nobile  3 , Georg Baumann  7 , Florian Feist  7 , Ulrich Müller  2
Affiliations

Characterisation of thermally treated beech and birch by means of quasi-static tests and ultrasonic waves

Hajir Al-Musawi et al. Sci Rep. .

Abstract

Wood, being renewable and highly abundant material, with excellent high specific strength and stiffness, has received increasing attention to be used in high performance applications such as the structural element of a battery case in an electric vehicle. For a successful implementation of wood in the automotive sector, it is, therefore, crucial to understand the behaviour of wood during and after temperature exposure and in the event of fire with the presence/absence of oxygen. In this study, the mechanical properties of thermally modified and unmodified European beech and birch in air and nitrogen environments at six different treatment intensities were characterised using compression tests, tensile tests, shear tests and Poisson's ratio tests. Further, the elastic properties of these wood species were quantified using the ultrasound measurements. The obtained strength and stiffness exhibited mild improvement upon moderate temperature treatment (200 °C), followed by a decrease at elevated temperature levels. This improvement was somewhat more pronounced under nitrogen treatment than under air treatment conditions. Nevertheless, a more noticeable decrease in the material performance was observed in beech compared to birch, occurring at earlier stages of modifications. This study confirms the tension-compression asymmetry of beech and birch where higher Young's moduli were obtained from tensile than from compression tests for reference and thermally treated beech and birch. The shear moduli obtained from ultrasound for birch were comparable to those obtained from quasi-static tests, whereas there was an overestimation of approximately 11-59% for the shear modulus of beech compared to quasi-static tests. Poisson's ratios from ultrasound tests corresponded well with those from quasi-static tests for untreated beech and birch, but not for thermally modified samples. The Saint-Venant model can satisfactorily predict the shear moduli of untreated and treated beech wood.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Specimen geometry for quasi-static tests (dimensions given are in mm).
Figure 2
Figure 2
Thermal treatment in an inert atmosphere.
Figure 3
Figure 3
Specimens used for ultrasound measurements with different orientations.
Figure 4
Figure 4
Ultrasound experimental setup.
Figure 5
Figure 5
Longitudinal tensile strength (ftL) of beech and birch.
Figure 6
Figure 6
Tensile modulus of elasticity (EtL) of beech and birch.
Figure 7
Figure 7
A comparison between experimental shear modulus (G-exp) with predicted values (G-pre) using the Saint-Venant model for beech and birch (a: air condition; n: nitrogen condition).
Figure 8
Figure 8
A comparison between experimental shear modulus (reported in Gòmez-Royuela et al. ) with predicted values using the Saint-Venant model for untreated and modified beech.
Figure 9
Figure 9
Mean values for the Young’s moduli of reference and heat-treated beech and birch obtained by ultrasound (US) and quasi-static tests (Co: compression; Te: tension).
Figure 10
Figure 10
Mean values of the shear moduli of reference and heat-treated beech and birch obtained by ultrasound (US) and quasi-static tests (Co: compression; Te: tension).
Figure 11
Figure 11
Mean values for the Poisson’s ratios of reference and heat-treated beech & birch obtained by ultrasound and quasi-static tests.
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