Using acoustic waves to probe structural anisotropy in brittle foams.
Abstract
We use low frequency ultrasonic waves (50 kHz) to investigate the mechanical properties of anisotropic freeze-dried bread foams that were prepared by applying uniaxial stress to fresh breadcrumb. Longitudinal ultrasonic velocity and amplitude measurements were taken in directions parallel and perpendicular to the compression direction. The velocity was found to decrease as the amount of compression is increased, with the decrease being greater in the parallel direction. The velocity data were interpreted using two theoretical models, one based on the static compression of a simplified strut model of foams and the other including the effects of tortuosity on wave propagation through anisotropic media. Both models allowed the velocity anisotropy to be directly related to the anisotropy of the foam structure, and give predictions in good overall agreement with the data. The results also allowed us to conclude that there must be a weakening of the cell walls caused by the uniaxial compression in addition to the effects resulting from the anisotropy alone.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2004
- Bibcode:
- 2004APS..MARH21006E