Global preheating and local cooling (GPLC) is an efficient method for temporarily opening closed cracks. In GPLC, a saturated duration that is the time period while a closed crack tip is imaged by linear phased array (PA) can affect the measurement accuracy. Here, we proposed an estimation method for the saturated duration based on the analytical solution. First, we derived the analytical solution of crack depth d (t) in PA images during GPLC, based on heat transfer and thermal stress analyses and the assumption that closed cracks become open when the sum of the thermal stress and the tensile stress of incident wave equals to crack closure stress σ_c . Based on the analytical solution, the saturated durations were estimated. The values estimated agreed well with the experimental results. The analytical method was also verified by the good agreement in d (t) between the analysis and the experiment.

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