# Curvature regularization near contacts with stretched elastic tubes

## TL;DR

This paper reveals a novel curvature regularization mechanism in stretched elastic tubes near contact points, driven by geometry and mechanics, independent of bending rigidity, with implications for contact behavior and drag reduction.

## Contribution

It introduces a new mechanism of curvature regularization in elastic tubes under axial stretch, distinct from bending rigidity effects, supported by experiments and theory.

## Key findings

- Curvature radius increases with applied stretch force.
- Regularization mechanism is independent of bending rigidity.
- Axial force reduces contact area, affecting drag.

## Abstract

Bringing a rigid object into contact with a soft elastic tube causes the tube to conform to the surface of the object, resulting in contact lines. The curvature of the tube walls near these contact lines is often large and is typically regularized by the finite bending rigidity of the tube. Here, we show using experiments and a F\"{o}ppl--von K\'{a}rm\'{a}n-like theory that a second mechanism of curvature regularization occurs when the tube is axially stretched. The radius of curvature obtained is unrelated to the bending rigidity of the tube walls, increases with the applied stretching force and decreases with sheet thickness, in contrast with the effects of finite bending rigidity. %Moreover, the axial force decreases the contact area between the tube and the intruding object, potentially reducing the drag necessary to propel the object through the tube. We show that these features are due to an interplay between geometry and mechanics specific to elastic tubes, but one that is absent from both planar sheets and spherical shells.