Rupture of rubber. X. The change in stored energy on making a small cut in a test piece held in simple extension

Application of the tearing energy criterion (Part I of this work) to the problem of the tearing of a rubber strip that contains a small cut or tear of length c in one edge and is stretched in simple extension is based on the relation W i – W = K (λ) c 2 hE , where W i and W are the total stored energies of the strip in the absence and presence of the cut, respectively, h is the thickness λ 0 of the strip, E is the stored‐energy density in the central region of simple extension, and K (λ) is a numerical factor that varies with the extension ratio λ in this region. An experimental method is described for measuring ( W i – W ), which enables the factor K (λ) to be evaluated. The results indicate that K (λ) decreases from a value of about 3 at low extensions to a value somewhat below 2 at λ = 3. The experiments also provide a more stringent test of the accuracy of the above relation than has been possible hitherto.