Delamination in timber induced by drying

Abstract

Delamination is the separation of wood fibre cells in the context of solid wood product such as timber board. Wood is a natural composite material with anisotropic properties. In the context of wood drying, delamination can be regarded a form of degrade due to poor drying condition or due to wood properties such as wood with low strength. In wood drying, these defects are commonly known as surface checks, internal checks and end splits on timber boards. Some basic concepts of drying have been elaborated in this chapter, following the prediction of drying time, developed drying stress, strain on the board surface and centre for a range of drying schedules using mathematical models both for a hardwood and a softwood. The combined drying and stress model can be helpful to optimize drying process that can reduce delamination in solid wood during drying. The higher the drying temperature, the shorter will be the drying time. However, the likely developed stress during drying is predicted to be higher due to aggressive drying conditions. The optimum drying condition seeks the trade-offs between these two opposing behaviors thus developing drying schedule that dries timber in least time and without significant degrade such as delamination. This is the main goal of many timber drying research programs.