Material key curves are functions providing a relationship among load, displacement and crack size, and are used in fracture mechanics methods for ductile polymers. This work shows that the material key curves provide also a tool to distinguish among different deformational mechanisms involved in the fracture process and they reflect the constraint degree. Tests are carried out on an acrylonitrile-butadiene-styrene resin (ABS) as a model material, and different deformation mechanisms are induced by different temperatures and loading rates, up to impact conditions. Deformation mechanisms are investigated, for the first time on ABS, by tomography and the results are compared to more traditional imaging techniques as scanning and transmission electron microscopy.