Influence of foreleg microstructure and nanomechanical behavior on torsional performance in the transient landing impact of the Chinese stag beetle, Dorcus hopei Saunders.

Abstract

The Chinese stag beetle (Dorcus hopei Saunders) is highly mobile. Its ability to land steadily on complex surfaces offers bionic inspiration for research on the landing systems of flapping-wing micro air vehicles (FWMAVs). In this paper, the foreleg structure of this beetle was studied using Micro-CT 3D reconstruction technology. The nanomechanical properties of its foreleg were investigated by nanoindentation. The role of the torsional behavior in material properties during the landing process was clarified. It was found that the Young's modulus (Er) and nano-hardness (H) at seven representative positions of the foreleg (from the femur to the pretarsus) all showed a trend of first increasing, then decreasing, and then increasing again, which indicates that the biomaterials of the beetle's foreleg have adaptability in redistributing the landing load. Based on this, three foreleg models were established using the Ansys Workbench 2024R1 software to simulate the torsional performance of the foreleg during transient landing impact motion. The results showed that the beetle's foreleg exhibits decent mechanical properties with equivalent stress distribution and torsional resistance. To further study its torsional resistance, three-unit element section models were designed and investigated. The results demonstrated that the foreleg's cross-sectional structure offers significant advantages in resisting torsional deformation and enabling stable landing. This study provides bio-inspiration for the development of FWMAVs landing systems. STATEMENT OF SIGNIFICANCE: This study provides a significant advancement in bio-inspired engineering by systematically unraveling the mechanoadaptive biomaterial strategy and torsion-resistant structural architecture of the Chinese stag beetle's foreleg, Dorcus hopei Saunders. We move beyond qualitative observation to establish a quantitative structure-property-performance relationship, first revealing a unique spatial gradient in nanomechanical properties (Young's modulus and hardness) along the foreleg. This gradient is identified as a key biological mechanism for optimal landing load redistribution. Furthermore, through bio-inspired computational models, we demonstrate that the foreleg's specific cross-sectional configuration confers torsional stability. These findings offer a foundational, data-driven design framework for overcoming a critical challenge in flapping-wing micro air vehicle (FWMAV) development-achieving controlled and stable landing on complex surfaces. Our work thereby bridges functional biology and advanced robotics, paving the way for a new generation of impact-resistant and agile micro-aerial systems.