Test for the deep: magnetic loading characterization of elastomers under extreme hydrostatic pressures

Abstract Soft robot incarnates its unique advantages in deep-sea exploration, but grapples with high hydrostatic pressure’s unpredictable impact on its mechanical performances. In our previous work, a self-powered soft robot showed excellent work performance in the Mariana Trench at a depth of 11 000 m, yet experienced notable degradation in deforming capability. Here, we propose a magnetic loading method for characterizing elastomer’s mechanical properties under extremely high hydrostatic pressure of up to 120 MPa. This method facilitates remote loading and enables in-situ observation, so that the dimensions and deformation at high hydrostatic pressure are obtained and used for calculations. The results reveal that the Young’s modulus of Polydimethylsiloxane (PDMS) monotonously increases with pressure. It is found that the relative increase in Young’s modulus is determined by its initial value, which is 8% for an initial Young’s modulus of 2200 kPa and 38% for 660 kPa. The relation between initial Young’s modulus and relevant increase can be fitted by an exponential function. The bulk modulus of PDMS is about 1.4 GPa at 20 °C and is barely affected by hydrostatic pressure. The method can quantify alterations in the mechanical properties of elastomers induced by hydrostatic pressure, and provide guidance for the design of soft robots which serve in extreme pressure environment.