Prediction of linear dimensional change of unrestricted wood at different levels of Equilibrium Moisture Content

A computer routine to predict variations in linear dimensions and warping of wood was designed and tested. This routine was applied on both experimental data obtained from laboratory-prepared wood samples as well as other data found in the literature. The two outcomes were compared and contrasted. Predictions resulting from the computer procedure resulted to be reliable only for wood which is straight grained and free from physical constraints and natural defects 1. AIM The aim of the computer analysis exercise was to predict linear dimensional changes as well as any possible warping (cupping) of unrestricted wood. 2. METHOD A computer routine was devised by using two computer software packages, namely Microsoft Excel and AutoCAD 2000. Data found in the relevant literature was used in order to carry out the necessary workings. The four stages of the computer analysis routine consist of: (i) the end grain photography and line drawing on AutoCAD; (ii) the merging of data into a Microsoft Excel spreadsheet; (iii) the interpretation of data and the relevant calculations; and (iv) the re-construction of the panel end grain, considering the predicted contraction/expansion and warping using AutoCAD. 2.1.End grain photography and line drawing by AutoCAD The first step involved capturing an image of the end view of the panel. In this study, both direct scanning and digital photography were applied. One has to consider that photography has an element of inaccuracy due to perspective illusion. The picture was transferred into AutoCAD and the outline traced. The drawing was then divided into a number of quadrilateral sections, as in the case of ABCD shown in Figure 1. In areas where the radius of curvature of the annual rings was quite small or complex, smaller quadrilateral sections were constructed. The diagonals in each section were then marked (as AD and BC in Figure 1) and th