Comparison of techniques for quantification of internal stress within industrial kiln-dried timber

For a quantification of internal stress within industrial kiln-dried timber, a comparison of a new restoring force (RF) technique is made against the McMillen slice test and the standard case-hardening test. Simulation of the RF has been performed by using a numerical model of finite element (FE) analysis. 30 mm thick industrial kiln-dried rubberwood timber with 58, 78 and 100 mm widths was used in the study. The measured RFs for each timber size are proportional to the released strain data measured by the McMillan slice test and the gap openings measured according to the case-hardening test. The FE simulated and measured RFs are in good agreement. The geometrical shape factor as functions of timber width and cutting depth ratio is derived so that the internal stress can then be calculated without accounting for the modulus of elasticity. The calculated maximum internal stresses of all the examined timber sizes fall into a single curve and linearly relate to the released strain data. The RF measurement has the potential to be an alternative method to the existing techniques for a reliable and meaningful assessment of drying stress within industrial kiln-dried timber.