Fibre directions at a branch-stem junction in Norway spruce: a microscale investigation using X-ray computed tomography

Abstract

The connection between branch and trunk in a tree must be strong enough to transfer all loads acting on the branch, and it is well known that such branch-stem connections are indeed very strong. In this paper, X-ray computer tomography is employed to investigate the local fibre orientation in the close surrounding of a knot in a Norway spruce specimen to better understand the origins of the mechanical strength of the branch-trunk connection. First, a wood specimen containing an entire knot from pith to bark was imaged with a voxel size of 52 µm. Subsequently, smaller specimens were cut from this original specimen and imaged again with increasingly higher resolution over four levels. With the highest resolution level (2.6 µm voxel size), the tracheids with smallest lumen were successfully traced. The results revealed how the direction of the fibre paths that start below the knot curve around it as the paths progress upwards to the region just above the knot, where the paths divide into two: one set of paths integrating with the knot on its top side and the other set continuing up along the trunk. Fibres that integrate with the knot at its top follow paths just before they continue into the knot, with a radius of curvature of only about 1 mm in both vertical and horizontal directions. No abrupt change of fibre pattern between latewood and earlywood is observed; rather, a continuous change of fibre direction across annual layers can be seen. The detailed characterisation of the local fibre structure around the knot provides new data that can explain the remarkable strength of the branch-trunk connection.

Improving the Performance Properties of Impregnated Wood with its Subsequent Utilization into a Biochar Sorbent

“…This method was originally used to detect and localize internal defects in logs (Shi et al, 2022b(Shi et al, , 2022c. With the continuous improvement of technology, it has become more widely used, for example, to check the density and moisture (Martin et al, 2021), to study the development of xylem (Lehnebach et al, 2021), the distribution of fiber texture at the junction of branches and stems (Hu et al, 2022). In addition, X-ray microscopic tomography has been used to study the microstructure and properties of acetylated wood (Sedighi Moghaddam et al, 2017) and wood impregnated with furfuryl alcohol resin (Liu et al, 2021).…”

Wood-Only Timber Frame Joints Inspired by Trees’ Branch Model, Part1: Structural System and Bending Performance

“…In this study, the growth formation model at branches 8,9,10) The loads excreted on a stem-branch junction are mainly self and wind loads, where the unidirectional flow of fibers, combined with the intrinsic features of the junction, provide the load transfer efficiency and ensure the survival of the tree structure 11) . On the other hand, the loads excreted on a frame structure are mostly lateral; hence, a hypothetical version of the growth model was approached by alternating the flow direction of the fibers in every second growth layer (Figure 1.2).…”

3D Printing of Flow‐Inspired Anisotropic Patterns with Liquid Crystalline Polymers

“…Anisotropic materials can be formed by living organisms such as the cellulose fibers in wood grains [ 1 ] and fiber bundles in osteons of bone. [ 2 ] Their microstructures are shaped with spatially tunable stiffness gradients and sharp orientation changes [ 3 ] in order to accommodate stresses and morphogenesis of the living organism in an efficient manner. [ 4 ] This freedom enables remarkable mechanical properties while keeping energy consumption low and using weak building blocks.…”