anisotropic material, experiment

Dear Sergey Litvinov:

Composite materials are (or can be made) anisotropic. Some of the test methods for these (composites) are on the internet. Perhaps this will spark some ideas in you.

David A. Smith

Is there a single crystal?

Michael Dahms

f'up2 sci.materials

Thank you. I'll try to find some information related to composite materials.

No, it is not. I mean continuous media.

Yes it is possible. There is no ambiguity in the physical meaning of the relationships.

However, it is very rare that a continuous material will have so few symmetry elements that all 21 elastic constants will be non-zero. A material with three orthagonal symmetry axes (orthorhombic) has at most 9 independent constants.

See Nye's book on the properties of crystals, oxford press, 1957 for a complete discussion.

Various lecture notes on the web address the same topic; search for "elasticity", "symmetry", "constants", "Cijkl", etc.

See Dr. Kirz's notes at:

There are several standard tests for determining ultimate resistance properties but also elastic properties of long fibre reinforced materials. Obviously it is not possible to measure alla the elastic properties with one test.

See ASTM 3039, 3515....

........

While determining all 21 constants must be possible by imposing strains and measuring responses it is not easy to do. In the most general case a large number of difficult measurements will be required.

You might consider meaurements that involve photoelastic coatings to gather a lot of data with a single experiment. For example, one might drill a deep hole in a sample's surface, then impose a well defined stress (or strain) state far from the hole. A photoelastic coating will show the local strain state around the hole. The details of the local strain state are determined by the local boundary conditions, elastic constants, and remote strain field.

As a simple example, consider cutting a square sample from a plate and drilling a small hole in the center. Impose a uniaxial deformation at the sample boundaries. The local strain field expected around the hole for an ideal isotropic material is well known; deviations from that field must be due to non-zero elastic constants.

A single crystal is a continuous medium. You are talking of a polycrystal?

Michael Dahms

Somebody uses Speckle interferometry. Ciao Ghigo

Thanks a lot. Now I have enough information (as a theorist). Dr. Kirz's notes at:

Some ASTM links (by Ghigo) and the description of the experimental procedure (by dave martin) were also very useful.