The measurements performed in the experiment "Elastic deformation, Hooke's law" (C 14833) on a copper wire, which had been limited to elastic deformations at small stresses, will be extended here to larger stresses. When the yield stress is exceeded, plastic, i.e. irreversible deformation is observed. A further increase of the stress beyond the rupture strength, leads to rupture. A 40 cm long piece of wire is suspended on a lab stand, and carries a tray on which weights can be deposited. A pillow under the tray will dampen the fall when the wire ruptures. The loading of the tray occurs in three steps : First, 2 kg cause a clearly visible elongation. The addition of 1 kg results in a slow length change of several centimeters, the wire "flows", until "work hardening" leads to a constant elongation. The addition of only 200 g finally leads to rupture, as the rupture strength is exceeded.