The tree fungus Fomes fomentatrius (F. fomentarius) also known as “tinder fungus” has a strong, light and tough fruiting body, which makes it interesting as a cellular solid that can serve, for example, as a blueprint for lightweight construction. The visible part of the fungus, the fruiting body, consists of several parts, of which the hymenium stands out with its honeycomb-like structure[1,2]. The material consists of hyphae, fiber-like cells that are arranged in a tubular structure (honeycomb). This arrangement leads to low density compared to other parts of the fruiting body and at the same time to transversely isotropic mechanical properties. On the macroscopic scale buckling of the tubes and cracking of their walls are the main damage mechanisms. Furthermore viscoelastic recovery can be seen in the wet state [2].

Next to chemical and structural analysis we inspected the hymenium with phase-contrast enhanced computed microtomography. We investigated two different loading directions in situ: Parallel and transversal to the tubular structures of the honeycomb. In both cases, a morphological analysis of the microstructure was carried out, i.e. area fraction profiles, granulometry and fiber orientation. Further, we used 3D optical flow for motion estimation, as it allows voxel-wise tracking of displacements over the course of the compression steps. This allows correlating displacement fields with observed damage and fracture. Additionally we compare damage behaviour of dry and wet samples.

In summary, we showed how nature resits early failure by intelligent structuring on different length scales. Furthermore, we showed that the 3D optical flow method could also be used for complex structured biological materials.

References
[1] 1. C. Müller, S. Klemm, and C. Fleck, Appl. Phys. A 127, 178 (2021).
[2] R. Pylkkänen, D. Werner, A. Bishoyi, D. Weil, E. Scoppola, W. Wagermaier, A. Safeer, S. Bahri, M. Baldus, A. Paananen, M. Penttilä, G. R. Szilvay, and P. Mohammadi, Science Advances 9, eade5417 (2023).