We use the projected fringes technique to follow the changes induced in the topography of metallic sample sheets subjected to uniaxial tensile tests. Since in-plane strains are associated with out-of-plane deformations, the monitoring of thickness variation of the tensile specimens can be used to detect necking and shear band formation. A sequence of images of the fringe pattern was captured and processed by means of the Fourier transform technique. We measured the material behavior in the elastic and plastic zones during its elongation until fracture took place. We present experimental results for stainless and hot rolled steel sheets.