Quasi-Static FEA Model for a Multi-Material Soft Pneumatic Actuator in SOFA

The increasing interest in soft robotics has led to new designs that exploit the combination of multiple materials, increasing robustness and enhancing performance. However, the combination of multiple non-linear materials makes modelling and eventual control of these highly flexible systems challenging. This article presents a methodology to model multi-material soft pneumatic actuators using finite element analysis (FEA), based on (hyper)elastic constitutive laws fitted on experimental material characterisation. Modelling in SOFA, a FEA software, allows to simulate and control in real-Time soft robotic structures. One of the novelties presented in this paper is the development of a new user-friendly technique for the mesh partitioning in SOFA, using MATLAB algorithms, that allow the creation of uniform and more refined meshes and a mesh domain partitioning that can be adapted for any geometry. As a case study, a cylindrical multi-material soft pneumatic actuator is considered. It is composed of an internal chamber, which is constituted of an autonomous self-healing hydrogel, modelled as a hyperelastic material, and an external elastic reinforcement, made of thermoplastic polyether-polyurethane elastomer (TPPU), approached as a linear elastic material. The simulation of the combination of a hyperelastic and a linear elastic material in a single design is another contribution of this work to the scientific literature of SOFA simulations. Finally, the multi-material model obtained with the new mesh partitioning technique is simulated in quasi-static conditions and is experimentally validated, demonstrating an accurate fit between simulation and reality.