Size effects in the processing of thin metal sheets

The present investigation addresses the influence of grain sizes on the processing of thin metal sheets. The problem was approached in two different ways: firstly, by reduction of the sheet thickness at a constant grain size (investigated in tension), and secondly, by changing the grain size at a constant sheet thickness (investigated in bending). The material investigated was soft aluminum sheet, with thickness ranging from 0.17 to 2 mm. As the thickness of the specimens was chosen relatively high, geometric similarity with thin sheet materials was obtained by increasing the grain size by recrystallization. In this way the grain sizes ranging from 0.016 to 600 mm2 could be obtained. The results show that in both the experiments, the yield strength as well as the maximum load decrease with a decreasing number of grains over the thickness. For grain sizes larger than the specimen thickness, the value of the yield strength appears to increase with the grain size, whereas a strong increase of the variation is observed. The effect of this variation of material properties on the processing of these materials is demonstrated in a planar blanking process.