Full-field moisture induced deformation in Norway spruce: intra-ring variation of transverse swelling

TL;DR

This study investigates the full-field transverse hygro-expansion of Norway spruce at the growth ring level using digital image correlation, revealing how different tissues contribute to deformation patterns.

Contribution

It introduces a non-destructive digital image correlation method to analyze intra-ring moisture-induced deformation in Norway spruce, supported by a simple FE model.

Findings

Radial strains peak in dense latewood, following density progression.

Tangential and shear strains are relatively constant, except at sample edges.

A three-phase FE model aligns well with experimental data.

Abstract

The transverse hygro-expansion of the Norway spruce wood is studied on the growth ring level using digital image correlation. This non-destructive technique offers the possibility to contactless study deformation fields of relatively large areas. The measured full-field strains are segmented into individual growth rings. Whereas radial strains closely follow the density progression with the maximum in the dense latewood, tangential and shear strain remain constant except for positions around the edges of the sample. A simple FE three phase growth ring model is in good agreement with the experimental values. The selective activation of individual phases like earlywood, transitionwood and latewood demonstrates that the radial hygro-expansion is dominated by the earlywood deformation, whereas tangential deformation is a complex interplay of expansion and compression that needs all tissues to fully develop.