Preliminary Experimental Characterization of Pressure-Dependent Stiffness of a Granular Jamming Structure

Abstract

Granular jamming enables switchable stiffness modulation through vacuum-induced particle confinement and has attracted increasing interest in variable-stiffness robotic systems. However, quantitative characterization of pressure-dependent mechanical behavior remains limited. This study experimentally investigates the relationship between vacuum pressure and structural stiffness using a cylindrical granular-jamming specimen subjected to impact and static three-point bending tests. Coffee granules enclosed within an elastomeric membrane were evaluated under vacuum pressures ranging from 0 to −10 kPa. Under quasi-static loading, beam deflections were converted to equivalent Young’s modulus using classical beam theory, whereas the impact measurements were used to derive an apparent impact-response metric for relative comparison. Both loading conditions exhibited pressure-dependent increases in stiffness accompanied by reduced beam deflection. The static loading configuration showed an approximately linear pressure–stiffness relationship, whereas the impact tests exhibited nonlinear behavior at higher pressure levels, indicating that the apparent mechanical response depends on the loading condition. The results demonstrate that loading conditions influence the measured stiffness characteristics and should therefore be considered when evaluating granular-jamming structures. The presented methodology provides preliminary experimental characterization data that may support the design and evaluation of pressure-controlled variable-stiffness mechanisms for robotic and adaptive mechanical systems.