Contact mechanics of soft granular materials with capillary interaction

Engineering applications of soft granular materials require accurate characterisation of their mechanical properties (e.g., Young’s modulus). However, the formation of liquid bridges between the high-water-content surface and substrate introduces capillary forces, which adds complexity to contact mechanics and potentially compromises measurement accuracy. In this study, we conducted indentation tests on individual hydrogel particles to investigate the effects of capillary force on force-displacement curves. These effects were analysed by quantifying and tracking the curvatures of the liquid bridge during tests from image processing. Our results demonstrate that Young’s modulus estimation from raw data was overestimated compared to that obtained after accounting for capillary contributions. By isolating and correcting for capillary force contributions, this study provides an improved and reliable experimental method for accurately characterising the mechanical properties of soft granular materials, ensuring for safe and effective use in various critical applications.