# Biomimetic Assessment of 3D-Printed T-Shape Joints Bio-Inspired by the Stem-Branch Junction in Common Ash (Fraxinus excelsior L.) Trees

## TL;DR

This study uses tree junction structures to inspire 3D-printed T-joints that are stiffer and more efficient than standard designs.

## Contribution

The novel contribution is the bio-inspired design of asymmetrical T-joints based on the microstructure of common ash tree junctions.

## Key findings

- Asymmetrical 3D-printed joints were 2% stiffer than symmetrical ones in the elastic region.
- The interlocked area redistributed shear strain, improving junction performance.
- Bio-inspired designs maintain structural efficiency across multiple configurations.

## Abstract

The stem–branch junction in trees demonstrates exceptional structural design. This study examined two key features of the branch junction in common ash (Fraxinus excelsior L.) wood: the interlocked area (ILA) formed above a knot and the spatial arrangement of fibers in the junction. Bio-inspired by the microstructural features revealed by micro-computed tomography imaging, we developed 3D-printed models and compared their mechanical performance to standard symmetrical T-joints. We evaluated the models using mechanical tests and finite element modeling (FEM). Asymmetrical 3D-printed joints mimicking vessel and fiber distribution in the stem–branch junction were 2% stiffer in the elastic region than symmetrical joints and showed, on average, 10% lower deflection at failure. While the ILA had minimal effect on elastic stiffness, measured surface strain analysis indicated that it positively influenced the redistribution of shear strain in the junctions. Thanks to the bio-inspired design, the joints were stiffer and can be utilized in multiple design configurations while maintaining the same underlying principle.