Dynamics of Plastic Deformation Fronts in an Aluminum Alloy

aluminum-magnesium alloy samples (type 5052) with a nominal content of 2.5% magnesium and 0.25% chromium. The bone-shaped (see Fig. 1) samples have a gauge length of 102 mm, are 12.7 mm wide, and 1 mm thick. One end of the sample is fixed while the other is displaced at a constant speed. We measure the force needed to maintain this constant speed and acquire video images of the fronts. From the force measurements we can calculate a nominal stress (forceyarea), assuming a cross-sectional area of 12.7 mm 2 for all samples. We visualize the fronts with the shadowgraph technique [18] common in hydrodynamics. The sample is polished, and parallel light is reflected from it. Any roughening of the surface creates divergences of the parallel light, which are then detected by a video camera focused slightly off of the sample surface. Profilometer measurements show that this technique detects deformations of less than 1 mm. A deformation front visualized in this way is shown in Fig. 1. Obtaining a single front to study is not straightforward. Fronts usually form in pairs at a weak point in the sample