Influence of strain rate on stress changes during Lüders bands formation and propagation

Characterization of the Lüders bands that occur in niobium microalloyed steel is carried out in different points of their formation and propagation. During static tensile testing infrared thermography is simultaneously used to record temperature changes and digital image correlation to determine the strain amounts in specific points of Lüders bands formation and propagation. Temperature changes which present stress changes were taken at the different strain amounts 0.005 mm/mm, 0.013 mm/mm, 0.026 mm/mm and 0.032 mm/mm. Performed static tensile tests showed the influence of different strain rates 1.8·10−3 s−1, 7·10−3 s−1 and 1.85·10−2 s−1 on the stress changes during Lüders bands formation and propagation. In different specific points such as Lüders band front, behind the Lüders band front (deformed area) and in front of the Lüders band front (undeformed area) tests were carried out. The studies revealed maximum stress changes behind Lüders band front and their increase with increasing strain rate. At the highest strain rate in the point of maximum stress behind the Lüders band front the greatest temperature changes was measured.