The Myth of Softening behavior of the Cohesive Zone Model Exact derivation of yield drop behavior of wood

It is shown that the postulate of strain softening of the fracture stress is based on the error to regard the nominal stress to be the actual, ultimate stress, at the actual area of the fracture plan. Strain softening called yield drop is elastic unloading of the actual elastic stress at the intact, not ltimate, elastic loaded part of the specimen, outside the fracture zone. It appears that the Griffith theory only applies for the first yield drop until half unloading and further fracture follows from a ultimate stress criterion A small-crack merging mechanism explains precisely the “softening” called yield drop curve.