Bending rigidity of fluid-running tubes*

Cylindrical shells are elementary building blocks not only in engineering structural design but in mechanical functionality of soft materials or living things including blood vessels and bacteria. Still, their predictive modeling requires us to disentangle complex interplay between elasticity, geometry, and fluid-structure coupling.

Here, we study the rigidity and instability of cylindrical shells with fluids running inside it. This phenomenon is commonly seen in our daily lives such as showers and garden hoses.

 To see the effect of the running fluid, we measured the force needed for the deformation of the elastic tube while changing the velocity of the running fluid through a three-point bending test. We have clarified the relation between bending force and the running fluid-velocity. In particular, we have focused the critical force for the kink formation upon bending (known as the Brazier instability).

This study suggests to be a model case for calculating the rigidity and instability of elastic tubes and may also be applied to medical fields such as measuring the rigidity of blood vessels.