A novel modified deep drawing cup test with grooved specimens to reduce the effect of friction on the forming limit curve

Abstract This paper presents a proposal for a modified deep drawing cup test and its evaluation for the determination of the Forming Limit Curve (FLC), which is one of the most widely used characteristics for defining forming limits in sheet metal forming. The primary objective is to use the deep drawing cup test to streamline FLC determination across a broader spectrum of strain states and, through the modification, to eliminate the influence of friction on the tested material. Furthermore, specific specimen geometries and dimensions are proposed to ensure the evaluation of the entire forming limit curve. The optimized specimen design allows for covering the full range of major and minor strains, from uniaxial tension through plane strain to near-uniform biaxial tension, with the additional capability of investigating multiple thicknesses on a single specimen. In this study, the test is applied to X5CrNi18-10 (1.4301) austenitic stainless steel. Validation of the methodology and the accuracy of the results are verified theoretically using Finite Element Method (FEM) numerical simulations and practically through experimental testing on the selected material with a thickness of 0.5 mm. During the experimental procedures, strains are recorded and evaluated using Digital Image Correlation (DIC). In this case, surface major and minor strain analysis is performed using only a single camera, which simplifies the evaluation process. For comprehensive validation, the results are compared with the well-established and standardized Nakajima method for FLC determination.