An Experimental Study of Plane Plastic Straining of Notched Bars

Abstract

Test results are presented for symmetrically notched 1-in-wide steel and aluminum tension bars having a 0.30-in-wide net section between sharp 90-deg notches. They show clearly that the limit load is close to the plane-stress value for a ratio of specimen thickness to net width of 1/2 and is but half-way to the plane-strain value for a ratio of 6. Strikingly different behavior is exhibited by the thin specimens of steel and aluminum. The apparent raising of the yield strength of aluminum but not of the steel is explained by reference to the difference between the Mises and the Tresca criteria of yielding. Special coupon tests in which plastic deformation is restricted to out-of-plane shearing demonstrate the validity of this concept. Both longitudinal extension and lateral contraction data help to give a physical picture of the changes in the pattern of deformation from thin to thick bars. The great importance of concentricity of loading is brought out and the techniques of testing are described in considerable detail.