Stress drop, Luders strain and strain rate during serrated flow

Load and strain were recorded at every 1 ms interval during the serrated fl ow in annealed Al-4Cu-0.5Mg-0.5Mn alloy. The strain was measured by four mi nute strain gauges (0.15 mm length) stuck on the specimen at 0.5 mm interva ls. The Luders strain was 0.3%-1% and the Luders strain rate (maximum value ) was 0.1-0.6 s(-1) for average strain rates between 6 x 10(-5) and 3 x 10( -2) s(-1). The Luders band length was about 2-3 mm. In the test with the av erage strain rate of 3 x 10(-3) s(-1) two staged Luders deformation occurre d, that is, a fast deformation (0.1 s(-1)) was followed by a slow one (0.01 s-(1)). The current theory, which is based on the concept of the negative strain rate sensitivity of the flow stress, could not explain the experimen tal results mentioned above.