Tensile behavior of bio-inspired hierarchical suture joint with uniform fractal interlocking design

Hierarchical interlocking leads to optimal mechanical properties for sutures in nature. Inspired by this, a design method for describing a hierarchal triangular suture joint based on Koch fractal interlocking is developed. The effect of geometrical interlocking was examined by the analysis of the load transmission between joined parts. Samples of hierarchal suture joints were fabricated by using a high-resolution 3D printer and tensile tests were conducted to examine the mechanical behavior of these joints. The surface displacement and strain fields were obtained using the Digital Image Correlation (DIC) technology where the images were taken by a high-resolution microscope camera. Finite element models of the hierarchal suture joints were generated to simulate the tensile responses and to predict the stress distributions and failure modes. The numerical results show good agreement with the experimental data. The results of this study show that the second order suture joint with a sinusoidal center line exhibits not only high strength but also high ductility. Moreover, by increasing the hierarchical order from two to three, the stiffness and strength do not improve while the fracture toughness actually decreases, suggesting that increasing the fractal complexity does not always lead to the improvement of the structure's load-carrying capacity, even with low iterations for the fractal complexity. The results obtained in this study can serve as a guideline to the engineering design of suture joints with fractal interlocks.