Mapping full field deformation of auxetic foams using digital speckle photography

Measuring strain in foam presents a number of challenges. In the case of polymeric foam, the material is so soft that a conventional strain gage is not applicable because the rigidity of gage and its associated glue is stronger than the foam itself. Transducers such as clip gage, etc. may not be suitable either because the strain field may not be uniform within the gage length. Thus it is desirable that a non-contact and full field strain measurement technique be available. In this paper we introduce a speckle photography technique that is non-contact and can measure the full field deformation of a foam specimen. We use the natural texture of the pattern. Digitized images of the foam specimen under different loads arc "compared" using a special algorithm called CASI, to yield deformation maps of the specimen. Examples of applying this technique to testing PVC foam composites are presented in the paper.