“…That is to say, the integral dimensional measures or, intuitively, the area of all the fractal fracture surfaces tend in general to infinity, which makes all the traditional fracture energy vanishing. In fact, over the past decades, to overcome such a difficulty and well describe fractal characteristics of a fractal crack as a direct extension of the concept of traditional fracture energy, some new density kinds of fractal fracture energy parameters defined on a unit fractal measure were proposed, such as the specific energy-absorbing capacity of unit fractal measure (Borodich, 1992(Borodich, , 1997(Borodich, , 1999, fractal fracture energy (Bažant, , 1997a as well as the renormalized fractal fracture energy (Carpinteri, 1994;Carpinteri and Ferro, 1994;Carpinteri et al, 2002), which have been used widely in practical applications. However, as was pointed out recently by Ou et al (2014), such a concept of the fractal fracture energy seems now to be a little questionable, because these fractal fracture energies are both difficult to be determined in practice and lack unambiguous physical meanings (Bažant and Yavari, 2005).…”