Abstract
Fourier transforms are the basic tool in constructing different types of image filters, mainly those reducing optical noise. Some DIC or PIV software also uses frequency space to obtain displacement fields from a series of digital images of a deforming body. The paper presents series of 2D Fourier transforms of photo-elastic transmission images, representing large pseudo 2D granular assembly, deforming under varying boundary conditions. The images related to different scales were acquired using the same image resolution, but taken at different distance from the sample. Fourier transforms of images, representing different stages of deformation, reveal characteristic features at the three (‘macro-‘, ‘meso-‘ and ‘micro-‘) scales, which can serve as a data to study internal order-disorder transition within granular materials.
Highlights
Fourier transforms are the basic tool in constructing different types of image filters, mainly those reducing optical noise
There exists one more possible way of utilizing 2D Fourier transforms for granular materials – they can be regarded as a direct subject of analysis themselves [1], to Laue patterns in crystallography
The idea of the approach proposed in this paper comes from the certain similarities between poly-crystals and granular materials - the former show some kind of structural order, especially if so called ‘force chain’ network is studied
Summary
Fourier transforms are the basic tool in constructing different types of image filters, mainly those reducing optical noise. The Lauegrams are used to measure internal structure of crystals from distances between some ordered intensity peaks. The idea of the approach proposed in this paper comes from the certain similarities between poly-crystals and granular materials - the former show some kind of structural order, especially if so called ‘force chain’ network is studied. The important problem still left to be solved is the quantitative interpretation of the structure of ‘force chain’ network, observed in photo-elastic experiments. Some objective tool is necessary to measure characteristic distances and angles od these networks and to connect them with the way granular material deforms. The paper presents selected series of 2D Fourier transforms of photo-elastic transmission images, representing large (consisting of ~1e+6 grains) granular assembly, acquired during small scale geotechnical model tests
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