7. Strain Measurement in an Aluminium Foam by Means of Digital Image Correlation

Metallic foams represent a particular class of materials, characterized by their cellular internal structure, which are receiving a growing interest for lightweight construction and impact absorbers. The inhomogeneity makes it difficult to measure the strain with conventional techniques (e.g. strain gauges); on the contrary, an optical non-contact technique is particularly suitable, taking advantage of the naturally speckled surface. This chapter presents the application of the Digital Image Correlation (DIC) to the study of the response of an aluminium foam subjected to compression. A key aspect of the mechanical characterization of the foam is to evaluate the influence of the density on the sensitivity to the loading rate. The measuring technique encompasses two steps: first the displacements of a set of marker points are tracked using image analysis; then the strains are evaluated by means of a strain-displacement relationship, in which the markers play the role of the nodes in finite element modelling. The results allow for evaluating the evolution of the strains in the material during the compression test.