Dynamic response of earlywood and latewood within annual growth ring structure of Scots pine subjected to changing relative humidity

Abstract

Abstract Scots pine (Pinus sylvestris L.) was subjected to relative humidity (RH) changes, and the dynamic strain field on the surface and in the bulk wood was monitored by digital speckle pattern interferometry and X-ray computed microtomography assisted by digital volume correlation. If a freely shrinking specimen was subjected to an RH decrement, earlywood (EW) and latewood (LW) at the surface layer were deformed in the opposite directions at the beginning of drying due to moisture gradient across the specimen. As a result, the surface and core behaved as independent sub-components, with the surface restrained in its response by the dimensionally unchanged core. With time, both LW and EW shrank as moisture content (MC) became uniform across the specimen. When an entire wood specimen was restrained from movement and desiccated in ambient RH, EW was stretched to compensate for the considerable shrinkage of LW. Knowledge about surface deformation at the annual ring level as a function of varying RH may be helpful to assess the risks associated with the damage of paint layers caused by fluctuations of ambient RH.