3D X-ray tomography for the hygrothermal characterization of spruce wood

Abstract

The bio-based material considered in this work is spruce wood. Because of its complex morphology and high heterogeneity, this material still presents lacks of knowledge, concerning microscopic geometric changes, due to the hygrothermal solicitations. These changes lead usually to a considerable evolution of the resulting thermophysical properties of the material which constrains its use. The swelling and shrinkage phenomena, observed at the macroscopic scale, are the main witnesses reflecting such change caused by the hygric transfer history within the material. Indeed, the latewood/early wood transition present in the wood structure influences substantially the macroscopic behavior of the material, which is strongly dependent on the microscopic one. To answer these questions, a robust identification procedure based on very fine analysis tool is operated. It concerns an experimental investigation based on non-destructive 3D imaging technique "X-ray tomography". This method informs about the three-dimensional microstructure and also allows locating any heterogeneity in the material. The data processing was done using qualitative and quantitative approaches (phase connection, porosity...). Then, successive scans of the same specimen solicited at different hygric states provided the detection of its corresponding water field changes. This step required the development of an original device adapted to the tomograph for imposing constant relative humidity. The obtained results allowed to underscore the swelling phenomenon observed in such materials. In addition, specimens containing a latewood/early wood discontinuity are scanned, and the effect of that discontinuity on the porosity is analyzed.