Strain dependent viscous response describes the mechanics of cohesionless soft granular materials

Granular materials are ubiquitous in nature and are used extensively in daily life and in industry. The modeling of these materials remains challenging; therefore, finding models with acceptable predictive accuracy that at the same time also reflect the complexity of the granular dynamics is a central research theme in the field. Soft particle packings present additional modeling challenges, as it has become clear that soft particles also have particle-level relaxation timescales that affect the packing behavior. We construct a simple one-dimensional, one-timescale model that replicates much of the essence of compressed hydrogel packing mechanics. We verify the model performance against both 3D and 2D packings of hydrogel particles, under both controlled strain and stress deformation conditions. We find that the modification of a standard linear solid model with a strain-dependent prefactor for the relaxation captures the time-history and rate dependence, as well as the necessary absence of cohesion effectively. We also indicate some directions of future improvement of the modeling.