Analysis of the Temperature Evolution at Necking during Tensile Deformation of H240LA Steel Sheets

The study of localized necking based on strain analysis using Digital Image Correlation (DIC) is the most widely used technique in sheet metal forming to study the FLD (Forming Limit Diagram). However, due to the heat generated by plastic deformation during the forming operations, another way is to analyze the temperature field of the specimen during the test by using Digital Infrared Thermography (DIT). A series of Nakazima tensile tests of high-strength low-alloy steel were tested using DIC and DIT synchronized systems. In this study, a thermomechanical numerical model was developed in ABAQUS/Standard in order to study the energy balance between the different effects of heat generation by plastic deformation, and transient conductive and convective heat transfers through the sample and to the environment. Analysis of the predicted energy balance during the tests allowed to understand the temperature evolution observed both at the beginning and at the development of the unstable necking until fracture. The numerical results are consistent with the analysis obtained from experimental temperature field, making feasible the use of DIT systems to study new necking detection criteria.