Determination of the Bending Strength of Liquid Nitrogen-Treated Wood Using Two-Dimensional Digital Image Correlation

Abstract

The mechanical strengths of wood samples from three species were tested and compared – Uludağ fir (Abies bornmüelleriana Mattf.), oak (Quercus robur L.), and Oriental beech (Fagus orientalis L.) – after cryogenic treatment with liquid nitrogen (LN, −196 °C). Bending deformations were recorded by the ordinary method and two-dimensional digital image correlation (2D DIC) during bending tests. To apply the 2D DIC technique, a stochastic speckle pattern was sprayed onto the surface of each specimen and the displacement of these reference points was observed through non-contact during the bending tests. Deformation data obtained from the mechanical tests were compared with corresponding values ​​determined via 2D DIC for the control samples and the samples treated with LN for 15 and 30 min, to evaluate the accuracy and reliability of the method. The results demonstrated that LN treatment influenced the mechanical behavior of the wood to varying degrees depending on the treatment duration. Furthermore, the deformation measurements obtained via 2D DIC showed excellent agreement with the results from conventional measurement methods. These findings indicate that the 2D DIC technique can be a reliable and effective non-contact measurement method for investigating the mechanical behavior of cryogenically treated wood materials.