"Energy absorption in a bamboo foam"

A. Le Goff, L. Courbin, H.A. Stone, and D. Quere

Europhysics Letters **84** 36001 (2008)

## Soft Matter Keywords

bamboo foam, surface tension, energy absorption, Weber number

Figure 1. Image sequence showing a delrin sphere falling through a soap film. The sphere has a radius of 1.6mm and consecutive image frames are 0.8ms apart.

Figure 2. (a) Experimental setup for studying bamboo films. The sphere is released from a height h above the first film and comes to rest on the N+1 film. The bottom of the tube supporting the films is submerged in a water bath to prevent gravitational descent of the films and limit evaporation of the foam. (b) Spatio-temporal diagram showing trajectory of a particle through the foam. The y-axis is the vertical position of the projectile, while the x-axis is time. The slope of the projectile's trajectory is decreasing with time, indicating that the velocity is decreasing.

Figure 3. Plot of number of films, N, crossed by a projectile with impact velocity, V. Impact velocity is defined as the velocity of the projectile when it hits the first film.

Figure 4. Total surface energy, <math>E_S</math>, dissipated by the N crossed soap films as a function of total mechanical energy, <math>E_p</math>, injected by the projectile.

Figure 5. (a) Deflected trajectory of a stainless-steel sphere pass through a soap film at an oblique angle. (b) Maximum deformation of the film during the sphere's crossing. Note that the deformation occurs in the direction normal to the film surface.

Figure 6. Variation of the quantity <math>\beta We</math> as a function of <math>\alpha</math>. Angles <math>\alpha</math> and <math>\beta</math> are as labeled in Figure 5a.

## Summary

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## Practical Application of Research

Foams are under consideration for use in systems designed to absorb kinetic energy from projectiles. These systems are deployed to protect internal contents, people, precious objects, and other fragile items. Foams present an attractive option because they are light, simple and fast to form, and inexpensive. This work shows that foams are capable of absorbing kinetic energy from projectiles and will eventually arrest them. Though not immediately practical, this work with ideal foams opens up the way for future studies of projectile interaction with real foams. The initial work to characterize projectile interaction with bamboo, staircase, and oblique foams will contribute to the understanding of interaction with real foams.

## Projectile Interaction with Foams

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written by Donald Aubrecht