Many methods exist for the nondestructive measurement of strain in crystalline materials, where the regular ordering of atoms generates a sharp signal when probed with x-rays or neutrons. In amorphous materials, localized strain information can be obtained by using techniques that probe the surface, such as optical or electron microscopy, but behavior at the surface does not typically mimic that in bulk material. Further, the strain fields are usually governed by the behavior around inhomogeneities such as inclusions, voids, and cracks.
Poulsen et al. have developed a technique for measuring strain distributions in amorphous materials. They exposed a bulk metallic glass based on magnesium, copper, and yttrium to high-energy x-rays, and then compressed it in situ. Two methods were used to analyze the nearly circular symmetric diffusion patterns, one based on Q space and the other on direct space, and both depend on the shift in the position of the first peak (relative to the uncompressed reading) for determining the strain in the sample. The experiments showed that the macroscopic stiffness of the material was less than one might expect from the nearest-neighbor bonding, due to rearrangement of the atoms on the scale of 4 to 10 Å. For the Q-space method, it is possible that this technique can be applied to polymer glasses using laboratory x-ray sources, where absorption is not an issue. — MSL
Nature Mater. 4, 33 (2005).