Analysis of sheared edge formability of aluminum

Abstract

Edge quality produced by shearing processes often leads to reduced material formability which was observed in multiple studies and summarized in the reference literature. The intention to make the sheared edge performance more predictable has motivated development of several experimental techniques such as the hole expansion test and the half dogbone tensile test. The paper presents a detailed review of published results for both of these techniques and illustrates very limited research dedicated to sheared edge performance of aluminum alloys. The experimental study, performed on a broadly used aluminum alloy, 6111-T4, illustrated the effects of cutting clearance on longitudinal, transverse and diagonal orientations of the trim line relative to the rolling direction. For all sheet orientations, increasing the cutting clearance resulted in a substantial reduction in material stretchability along the sheared surface. However, for all investigated conditions a cutting clearance of 5% of material thickness resulted in stretching performance similar to the standard tensile test. In this case the sheared edge does not affect the stretching behavior of tested material. The analysis of material prestrain on sheared surface stretchability for a variety of combinations of minor and major strains indicated that for the widely accepted industry standard gap of 10% of the material thickness, the prestrain has significant effects on stretchability which only gets stronger with increased thinning of the sheet in the prestraining process. For an extended clearance of 40%, the effect of prestrain was less visible indicating that the sheared edge has a stronger effect on these cutting conditions than prestrain.Analysis of the effect of the cutting angle on stretchability indicated that higher elongations were observed with cutting angles of 10° and 20° for broadly used 10% clearance compared to orthogonal cutting with an identical clearance.The results of half dogbone tensile tests were compared with the results of hole expansion tests performed on the same sheet material. This comparison indicated that a substantial amount of localization occurs in the hole expansion test and leads to a much higher hole expansion ratio for small cutting clearances compared to the total elongations observed in tensile tests. However, the local strains measured in the area adjacent to fracture in the tensile test were above the hole expansion ratio.