Abstract: Nut shells have good impact and fracture resistance, but many kinds of nut shells have suture structures with low bonding strength. Therefore, the mechanism of impact and fracture resistance of nut shells as a whole is important to study, particularly given that sutures maintain low bonding strength. In this study, we investigated the effect of the geometrical characteristics of sutures (morphology, thickness, and number) on the overall fracture resistance of walnuts, based on mechanical tests of C-ring samples, microstructure analysis after cracking, quantitative analysis of suture geometric model, and numerical simulations. We found that the cracking of walnuts was mainly caused by tensile stress, and the bonding strength was approximately 2.48?±?0.64 MPa. We discovered that the thickness of the suture was 1.55?±?0.32 times thicker than the shell, which improved the fracture resistance ability by more than 28.4%. The undulating and inclined morphology of the walnut suture also increased the fracture force. Additionally, an appropriate suture number reduced the cracking of walnuts. In conclusion, our study sheds light on the physiological function of walnut sutures from a biomechanical perspective and provides useful references for designing fracture resistance measures in thin shell structures.

Key words: Fracture resistance , · Walnut , · Suture , · Bonding strength , · Numerical simulations , · Biomechanics