The Influence of Edge Quality on Edge Stretching Limit for Aluminum Alloy 2016-01-0416

This paper presents the measurement and analysis of the edge stretching limit of aluminum alloy using digital image correlation. The edge stretching limit, also known as the “edge thinning limit,” is the maximum thinning strain at a point of edge failure resulting from tension; which may be predisposed by edge quality. Edge fracture is a vital failure mode in sheet metal forming, however it is very difficult to measure. A previous study enabled the measurement of edge thinning strain by using advanced digital image correlation but it did not consider how the edge quality could affect the edge stretching limit of aluminum alloy. This paper continues to measure edge thinning strain by comparing polished to unpolished AA5754, thus determining the effect edge quality has on the edge stretching limit. To enable the measurement by optical method for a very long and thin sample, a notch is used to localize where edge failure occurs. The notched edges of the various prestrained aluminum alloy samples are polished to eliminate surface micro cracks from punch machining. A dual camera 3-D digital image correlation system is used to measure strain during tensile testing in the thinning direction. The test results indicate that the both the pre-strain and the surface micro cracks do not have significant influence on the edge stretching limit of aluminum alloy.