This paper reports the experimental data of our'research concerning the yielding of mild steel plates under tensile stress. Yielding was induced at a longitudinal section of the plate by frictional force which was applied to the surface of the plate under uniaxial compression. An analytical explanation of the results was attempted by proposing a new coefficient of friction which was a constant relationship between the frictional force and the strain on the surface of the plate. The analytical explanation is supported by the results of our experiments.