Advanced imaging for early prediction and characterization of zone of Lüders band nucleation associated with pre-yield microstrain

The present study involves experimental investigation of thermal and strain fields associated with generation of pre-yield plastic microstrain during tensile loading of mild steel using imaging NDE techniques such as infrared thermography (IRT) and digital image correlation (DIC). A fast array based infrared detector is used to map the temperature distribution and a DIC system is used to map the strain distribution in local zones of the material. Studies reveal that dynamic thermal and strain response of the material observed before macroscopic yield point and their spatial distributions are found to have good correlation with phenomenon of pre-yield microstrain and related experimental findings. Techniques used not only offered the possibility of visualizing the thermal and strain distributions associated with pre-yield microstrain but also to predict and visualize the zone of nucleation of Lüders band much ahead of upper yield point.