In the previous paper, a Nonlineer-Defect-Model of the crack initiation by tensile deformations was proposed. Based on the assumption that there is a defect of mechanically nonlinear character in a one-dimensional crystal, at which Young's modulus E veries with the strain ε as E=Eo(1-βε), where Eo and β are constants, it has been found that the strain at the defect ε is given in terms of the stress σ as
ε=1/2β(1±√1-4βσ/E0)
and also β governs the fructure stress σc=E0/4β.
In this paper, the above model is developed further in order to explain explicitly the crack propagation. When it is assumed that nonlinear character of E depends on ε with a small time lag ξ as E=E0(1-βε+βξ(dε/dt)), then ε is defined as the solution of the following equation
εdε/ε2-1/βε+σ/βE0=dt/ξ.
The analytical solution has been obtained for each case of σ_??_σc. Of special interest is the solution for σ>σc, which is the formulated expression of the crack propagation when ε increases with time to infinity. Lastly, the applicability of the present model on the actual crack propagation in a three-dimensional body has been discussed.
