Theoretical prediction of SCC growth behavior -- Threshold and plateau growth rate

In this paper, a purely theoretical formulation was developed for a quantitative prediction of crack growth rate particularly in terms both of a threshold behavior and of a plateau growth rate in the da/dt-K diagram. The formulation was developed based upon the Faraday`s equation for metal dissolution and crack tip strain rate for a growing crack in an elastic plastic work hardening material under either rising load or constant load. The crack tip strain redistribution due to crack advance was taken into consideration in the formulation. The obtained formulation can not be symbolically solved and therefore, has to be solved numerically. Results showed that a threshold K and a plateau growth rate at higher K range were the result of crack tip strain rate dependence upon K. Namely, threshold behavior can be explained simply from a view point of crack tip strain rate effects. Validation of this formulation for prediction of SCC growth behavior was examined by use of experimental crack growth data for pressure vessel steels, stainless steels and a Ni-base alloy in high temperature water. Finally, the results from the theoretical prediction were compared with those obtained by the numerical simulator developed before.