Novel Speckle Preparation and Heat Insulation Method for DIC Strain Measurement at Cryogenic Temperature and Large Deformation Environment

BackgroundThe accuracy and reliability of digital image correlation (DIC) technologies are not only dependent on correlation algorithms but also strongly affected by the quality of the speckle patterns, especially under extremely low temperatures and large deformation conditions.Objective To overcome the challenge that the speckle patterns become more brittle and harder in the extremely low temperature experiments near liquid helium, and speckles cracking and shedding during the large deformation processes.MethodsNovel speckle patterns and fabrication technologies have been developed specifically tailored to extremely low temperatures and large deformation conditions.ResultsA novel spinning-coated speckle fabrication method based on PDMS silicone and TiO2 spherical particles was proposed, which can enable extremely low temperatures of DIC measurements above 20% strain. Using the 316LN stainless steel as a sample, the performances of several common speckles have been compared, and the strain localization and propagation had also been clarified.ConclusionsThe novel DIC full-field measurement method was validated with 316LN stainless steel, which confirmed that the speckles have excellent stability in the process of large deformation at extremely low temperatures. In addition, the formation and propagation processes of the slip bands for 316LN stainless steel have been revealed.