Photoelastic visualisation of stresses in an assembly of disks

Simulation of a simple shear test.

Diagram of the loading and displacement program
1 vertical loading; 2 shear to the left; 3/4 shear to the right; 5 shear to the left; 6 unloading

Photographs of the 4 stages in the full sample

Photographs of the 4 stages in a detailed area


A movie of the tests can be downloaded below. Be prepared that downloading can take several minutes. The files are quite big because of the high photographically quality of the images.
movie full sample (20Mb!!
movie detailed area (18Mb!!)
The nicest result is obtained when the media player is set in the repeat mode!

What do you see:
The model is formed by a number of transparent perspex disks with a thickness of 4mm. The disks become anisotropic for light when subjected to shear stresses. This effect can be made visible with polarised light. In this test a dark field circular polariscope has been used. This means that more light will be transmitted when the shear stresses are larger. However, since the phenomenon is based on the phase difference of light waves there will be a shear stress where the phase difference is just one wave lenght. In monochromatic light again a dark field would be visible. In areas with high shear stresses (e.g. the contact points between the disks) many of these dark areas (fringes) can be observed.
In this test white light has been used. Since white light is a composition of several different wave lengths the shear stress is not influencing all the colours in the same way. This causes that the white light is separated into different colours. That is why the fringes are coloured instead of black.
Black regions in clear areas are typical for locations where the shear stress is almost zero.


What is simple shear
This program allows you to examine the deformation in a body under stress. As a result of external forces a body will be deformed. The visible deformation is dependent on: the strain (e), the direction of major strain (alp), the rotation (o) and the volume change (v). The mentioned parameters can be varied interactively, where the effect is visualised in a dynamic deformation field. How does it work: open the program directly or download the program in some directory and start the program by mouse click. To visualize simple shear then e.g.: e=0.3; alp=45; o=18

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