On the initial shape of the softening function of cohesive materials

A linear softening function is accurate enough to predict adequately the observed maximum load size effect for current laboratory beams made of cohesive materials, notched or unnotched, even if the actual curve presents an initial plateau. The solution of the problem of extracting the softening function from a set of experimental peak loads is non unique; linear and trapezoidal softening functions can lead to very similar peak loads. To pick out the suitable softening curve one needs additional experimental information, such as the load-displacement curve.