Development of a special self-adaptive auxetic structure for protecting tree trunks from external damage

• Analysis of mechanical damage to tree bark. • Analysis of damage inside tree trunks. • Guidelines for designing an optimally designed auxetic protective structure. • Use of simulations for structure design is presented on a real case. • Manufacturing and testing of a protective structure on a conifer tree. The objective of this research is to present the development of an innovative tree protection structure. With the increasing population of wild animals, the number of tree trunk damages is rising. Similarly, frequent damages occur during intensive forestry operations and timber harvesting, where bark abrasions and direct mechanical injuries are common. For this purpose, a wire wrapping structure was developed, which allows for easy direct installation around the tree trunk. Numerical simulations were used in the design and optimisation of the protective net. An important innovation is the introduction of an auxetic structure, which allows for spatial expansion that is synchronous with the natural process of tree growth. Such structure also stretches along two axes as the trunk thickens, which is the exact opposite of how conventional materials behave. Due to the use of a steel-wire base, the structure is sturdy and durable with a good protective effect. On the other hand, the cellular pattern results in spring properties, which contribute to a moderate and constant surface pressure on the tree bark. The protective structure was experimentally manufactured and tested on an affected conifer tree Abies alba. Over a period of three years, it contributed to the stable recovery process of the tree's damaged bark and prevented further damage attempts.