2019 Volume 105 Issue 1 Pages 105-111
We constructed an automatic in situ fatigue observation system to monitor small fatigue crack behavior at the microstructural level. Applying a digital image correlation (DIC) technique in combination enabled us to continuously and automatically track and record microscopic deformation behavior. To verify the effectiveness of this system, we applied it to small fatigue crack evaluation in heat-treated low-carbon steel. The results demonstrated the feasibility, using our developed system, of automatically tracking and recording microstructurally small fatigue crack initiation and early growth behavior. By utilizing DIC analysis, we also succeeded in visualizing microscopic deformations such as inhomogeneous strain concentration by microstructures causing fatigue cracks and small fatigue crack opening-closing behavior. Although early stage fatigue crack growth rate accelerated compared to long crack data, it was consistent with long crack data by using ΔKeff calculated from crack open stress measured by DIC.