Digital image correlation at high temperatures for fatigue and phase transformation studies

Abstract

In this study, digital image correlation was used for two widely different cases to assess the potential and the limitations of the technique for applications at high temperatures. Specifically, digital image correlation was employed in hightemperature low-cycle fatigue experiments in a nickel-based superalloy and in phase transformation experiments conducted on bainitic steel in order to shed light on the microstructural processes. Depending on the type of experiments, the microstructure was characterized prior to the experiments (fatigue) or after the experiments (phase transformation). In the fatigue experiments, it was found that the features dominating damage evolution were the dendrites resulting from the solidification of the cast material. In the phase transformation experiments, variant selection is active when stresses are superimposed during the phase transformation process, which resulted in the evolution of transformation plasticity strains. Thereby, mainly the bainite variants oriented along the [101], [201] and [121] directions were observed to grow parallel to the loading axis, which in turn led to transformation plasticity strains. For validation of the digital image correlation data, average strains were calculated for the surface area probed and compared to strain values obtained by conventional extensometry. In all cases studied, the correlation was satisfactory, indicating that digital image correlation can provide for additional insight into processes active at the micro level.

Review of research progress and development trend of digital image correlation

“…This, in turn, induces a degradation in image quality characterized by the "de-correlation phenomenon". Holzweissig et al (2013) have emphasized that high-temperature thermal radiation is an unavoidable factor. Nonetheless, efforts can be directed towards mitigating thermal radiation through enhancements in experimental equipment.…”

The application of digital image correlation (DIC) in fatigue experimentation: A review

“…Holzweissig et al 125 combined DIC and EBSD in high‐temperature LCF tests to correlate local strain measurements with microstructural features like grain boundaries. The test frame was equipped with a high‐frequency induction heater and a digital microscope for imaging.…”

Cool, Dry, Nano-scale DIC Patterning of Delicate, Heterogeneous, Non-planar Specimens by Micro-mist Nebulization

“…Performing simultaneous electron back-scatter diffraction (EBSD) for crystallographic characterization along with DIC measurements can be of high interest, especially where it is important to understand the connection between the crystal/phase structure and the resulting microscale deformation. Examples of such multi-modal high-resolution analyses include analysis of fracture at the microstructural scale [55], change in grain orientation with deformation [55], twinning [56] or phase-transformation mediated deformation [57], or the role of complex microstructure on deformation [58,59]. While application of DIC in such cases requires a high-density pattern, simultaneous EBSD imaging requires a pattern that is transparent to the backscatter electrons coming from the top 10 nm region below the surface.…”