Measuring crack growth and related opening and closing stresses using continuous potential drop recording

To improve resolution of in-situ measurement of crack closure and opening in fatigue, potential drop (PD) measurement technique has been further developed to measure thousands of times through each load cycle with high precision. The results are interpreted with physical phenomena like strain, Poisson's effect, piezo-resistivity, plasticity, and crack growth. Application of the technique to fatigue crack growth tests on aluminum 2024-T3 CCT specimens at different maximum stresses and stress ratios, demonstrate that indeed variations in PD can be associated to development of plasticity and crack opening and closure. Hence, the technique allows to measure timing and magnitude of crack opening and closure stresses in-situ in fatigue crack growth experiments.