On the indentation of a fluid-filled spherical particle

• A continuum nonlinear particle model subjected to axisymmetric finite deformations is presented.
• The solutions are assumed to be axisymmetric, but no other geometrical assumptions are imposed.
• The indenter force, fluid pressure, principal stretches and stress are for various sharp conical indenters are considered and analyzed.
• This model can be used to determine the mechanical properties of soft particle from indentation experiments.
• It can also be used to predict the penetration conditions of capsules and for the microinjection techniques.

The indentation of small size soft particles is a widely used technique to evaluate the mechanical properties of such particles. In this paper, the particle is modeled as an inflated fluid-filled membrane structure. The proposed model is used to study the nonlinear deformations of the particle. We assume that the peripheral surface is a nonlinear hyperelastic, homogeneous and isotropic membrane, while the enclose fluid is incompressible. The particle is indented by frictionless rigid conical indenters, while supported by a flat plane. The equilibrium configurations are solved numerically to study the mechanical response of the particle. The indenter force, enclosed fluid pressure and stress distribution in the membrane are determined for various indenter shapes and initial inflations. This study provides a better understanding of the magnitude and location of the maximum stress in the membrane during indentation. The dependency of the indention force and fluid pressure on the material properties of the particle are also investigated.