In fracture, the various expressions of G the crack extension force per unit length of the crack-front (or energy release rate) show invariably a linear dependence of G with the crack half-length c. This is true whatever the shape (planar or non-planar) of the crack and the form f of the crack-front (f can be developed in Fourier forms). Hence some expressions of G (see relation (2.25), page 37 in Lawn (1993) Second Edition, for example) provided for the DCB specimens are under question. Are these concerned with crack propagation?