Abstract
A tentative attempt is proposed to interpret subcritical crack growth in brittle materials without any mention to stress corrosion. Based on theoretical and experimental results on adherence of viscoelastic solids on glass, where the true Griffith criterion (G = 2 γ) was observed, with crack healing for G 2γ, it is proposed that subcritical crack growth is a normal mode of propagation in any material. The crack velocity v results from a balance between crack extension force G — 2γ and losses at the crack tip, fonction of the crack speed and the intrinsic surface energy γ: $$G - 2\gamma = 2\gamma {\Phi _T}\left( v \right)$$ Crack propagation is stable only on branches of the ϕ(v) curve with positive slope. At a critical crack speed vc, dϕ/dv becomes negative, and the velocity jumps on a second positive branch. This criterion for crack speed unstability which defines the fracture toughness Kc must not be confused with the Griffith criterion.
Published Version
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