Abstract
There is a shortage of experimentally determined strains during sheet metal shearing. These kinds of data are a requisite to validate shearing models and to simulate the shearing process. In this work, strain fields were continuously measured during shearing of a medium and a high strength steel sheet, using digital image correlation. Preliminary studies based on finite element simulations, suggested that the effective surface strains are a good approximation of the bulk strains below the surface. The experiments were performed in a symmetric set-up with large stiffness and stable tool clearances, using various combinations of tool clearance and clamping configuration. Due to large deformations, strains were measured from images captured in a series of steps from shearing start to final fracture. Both the Cauchy and Hencky strain measures were considered, but the difference between these were found negligible with the number of increments used (about 20 to 50). Force-displacement curves were also determined for the various experimental conditions. The measured strain fields displayed a thin band of large strain between the tool edges. Shearing with two clamps resulted in a symmetric strain band whereas there was an extended area with large strains around the tool at the unclamped side when shearing with one clamp. Furthermore, one or two cracks were visible on most of the samples close to the tool edges well before final fracture. The fracture strain was larger for the medium strength material compared with the high-strength material and increased with increasing clearance.
Highlights
There is a shortage of experimentally determined strains during sheet metal shearing
Among the two symmetric sides of the set-up and the two experiments performed for each configuration, the difference in force was less than 1% and |Uy| varied a few percent at the point of fracture
These variations were smaller than the expected accuracy in the strain measurements, and strains were only calculated from one series of images for each combination of shearing parameters and material
Summary
There is a shortage of experimentally determined strains during sheet metal shearing These kinds of data are a requisite to validate shearing models and to simulate the shearing process. Shearing is a widely used process in the sheet metal industry and has been extensively studied to increase the understanding of the shearing mechanism, and to improve the industrial process with respect to parameters such as tool force, tool wear and sheared surface appearance. The appearance of the cut surfaces in the blanking process was studied by Crane (1927), who Gustafsson et al International Journal of Mechanical and Materials Engineering (2016) 11:14 characterised the surface appearance in terms of various zones. Micro-hardness testing of sheared samples was used by Weaver and Weinmann (1985) to study the deformation hardening in this region, and Dalloz et al (2009) showed that a heavily deformed sub-surface region contains crack initiating voids
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