A mechanical device including an elongated structural element provided for absorbing, at least in part, certain shocks by deformation. The structural element or piece has a selected right sectional profile, the profile being provided with localized alterations, shapes, and with selected respective positions for approximately satisfying a given law of deformation under the combined effort of compression in an axis of the piece and of the moment of the axis perpendicular to a plane passing through the axis. The law includes an energy absorption phase followed by a retraction of the piece.