# A Matter of Shape: Contact Area Optimization in Soft Lubricated Impact

## TL;DR

This study explores how the shape of a soft object affects contact during impact with a surface, showing that shape can be optimized to control fluid entrapment and contact pressure.

## Contribution

The paper introduces shape as a key design parameter for optimizing contact in soft lubricated impacts.

## Key findings

- Sharper object profiles like cones maximize central contact and avoid fluid entrapment.
- Blunter shapes create central dimples that trap bubbles during impact.
- Classical dry contact mechanics can predict pressure distributions in thin viscous films.

## Abstract

We study the fluid-mediated impact of a deformable axisymmetric object against a rigid substrate, focusing on how its shape influences contact formation. For low approach velocities and large Stokes numbers, we show that sharper profiles (e.g., conical) maximize contact at the center and avoid fluid entrapment, while blunter ones form central dimples that trap bubbles. We also find that the resulting pressure distributions in the presence of thin viscous films can be predicted remarkably well by classical (dry) contact mechanics. These findings reveal shape as a design parameter for contact optimization in soft matter, adhesion, and elastohydrodynamics. Finally, we also theorize the possibility of a mechanical equivalence between shape and approach velocity.

The online version contains supplementary material available at 10.1007/s11249-026-02108-1.