Methods for collecting and analysing simultaneous strain and moisture data during wood drying

Abstract: Improved understanding of moisture and mechanical behaviour is an international objective for wood drying research. The main objective of this licentiate thesis work was to develop an experimental method suitable for collecting valuable response data related to the moisture and mechanical behaviour of drying wood. Another objective was to provide an example on how multivariate methods can be used to analyse response data. A method for simultaneous non contact measuring of two dimensional surface deformations and interior densities have been developed. This was done using Digital Speckle Photography, DSP, and X-ray Computerised Tomography (CT). Displacements and densities were used for calculation of strains and moisture contents using a custom software developed in Matlab. Experimental tests of the measuring method were made on cross sections of Scots pine. The following accuracy was stated for different properties: - Displacements measured with DSP could be measured with a random error down to 0.01 pixels. A more typical calculated displacement error of approximately 10 micrometres, was found in paper I. - Strains derived from the displacements had a maximal error of 1.11 mstrain in an experimental test in paper II. - Accuracy in density measurements was expected to be less than +-6 kg/m3 for wet wood with moisture contents ranging from 6-100% and less than +-2 kg/m3 in dry wood, at a significance level of 0.05. This was estimated for a 2x2x1.5 mm3 measuring volume. - Moisture content measuring accuracy was estimated by simulations in paper II, which resulted in a measuring accuracy of +-1.8% moisture content at a significance level of 0.05 in a measuring volume with the approximate size of 2x2x1.5 mm3. A multivariate analysing method has been used to present an example on multivariate modelling of shrinkage behaviour in Radiata pine. The method was found to be an easy-to-use tool and useful for valid prediction of radial, tangential, longitudinal and volume shrinkage in the moisture range between 0% and 22% moisture content of the studied wood. The method also proved to be effective for untangling relationships between variables and generating information out of data. Finally, it can be stated that the developed measuring technique and the tested multivariate analysing method will be of use to improve the understanding of the behaviour of drying wood, focusing on moisture and mechanical properties.