Visualizing intra-ring transverse shrinking and swelling of Chinese fir

Abstract Wood’s hygroscopicity causes it to shrink and swell in response to changes in ambient humidity, which impact its performance in service. This study aimed to elucidate the hygro-deformation behavior of wood by conducting a two-dimensional visualization analysis of intra-ring transverse shrinking and swelling of Chinese fir [ Cunninghamia lanceolata (Lamb.) Hook.]. By combining digital image correlation with Greenhill theory, off-axis deformations were measured and analyzed, demonstrating the method’s capacity to visualize intra-ring dimensional changes. The predicted radial and tangential deformations, derived from off-axis measurements, aligned closely with experimental values. The two-dimensional analysis revealed significant differences in hygro-deformation between earlywood and latewood: earlywood exhibited a “peanut shell” like strain distribution, with most shrinking and swelling occurring in the tangential direction, whereas latewood displayed a nearly circular strain distribution with reduced anisotropy. These findings provide a basis for understanding the deformation behavior of rift-sawn boards and offer valuable insights for optimizing wood processing, drying, and dimensional stability control.