Pinching simulation of the coconut crab considering the 3D shape and internal characteristics of the robust claw exoskeleton

Abstract

A pinching simulation of the coconut crab, Birgus latro, which has a pinching force 80 times its body mass, was performed to quantify the stress imposed on the claw fingers when such a large force is applied. Data on the three-dimensional (3D) shape and internal information (hard exocuticle layer and soft endocuticle layer) in the claw exoskeleton were obtained using microfocus X-ray computed tomography. From these data, a 3D model of the claw was reconstructed using image analysis software, and a pinching simulation was performed using finite element analysis. The pinching force (R_f) was calculated as the sum of the node reaction forces in the area that came into contact with the stainless rod while the movable finger rotated within the claw, and the von Mises stress, σ_mises, in the fixed and movable fingers during the rotation were shown. The results showed that the stress increased with the angle of rotation, and at an angle of rotation of 2.8° and a reaction force of 957 N, stresses of 1.8 GPa were generated in the fixed finger, 588 MPa in the movable finger, and 674 MPa in the rod. This scientific pinching simulation confirmed the exceptional strength of the coconut crab's claw.