Novel assessment of casehardening in kiln-dried lumber

Casehardening within kiln-dried rubberwood lumber was assessed by means of a novel restoring force measurement on a half-sawn specimen and a released strain according to the McMillen slice test. The techniques were used to quantify the magnitude of internal stress within the kiln-dried lumber during cooling and conditioning. It was revealed that cooling under relatively high humidity after drying is an effective technique to relieve the internal stress within the kiln-dried lumber during conditioning. The measured restoring force strongly correlated with the differential released strain between the surface and the core layers obtained from the McMillen slice test. The proposed technique showed good potential to be an alternative means to quantify the magnitude of internal stress within the kiln-dried lumber either during or after processing.