Model metal matrix composites are fabricated on purpose in this study in order to analyse damage initiation in heterogeneous metals. The materials consist in titanium matrices reinforced with SiC cylinders or aluminum matrices containing spherical zirconial/silica inclusions. The damage mechanisms of these materials are studied qualitatively and quantitatively using 3D non destructive imaging techniques (X-ray absorption radiography or tomography). In the case of the cylinders, the strain to failure of the SiC fibres as well as the interface shear strength can be directly measured. These measurements are the first attempts of direct determination of such parameters in heterogeneous materials. In the particulate composites, the strain to failure of the particles is determined using an inverse finite element calculation which validates the normal stress and stored elastic energy criteria for the rupture of the ceramic spheres.