Determination of the formability limits for Grade 1 titanium sheet by means of ALSAD method

Abstract

Stamping is one of the most widely used sheet metal forming processes. Esthetics and durability of the deformed products are limited by defects in the form of strain localization, grooves or cracks. Forming limits, e. g. in form of forming limit curve (FLC), help to avoid above-mentioned defects in the sheet metal during forming. Besides the common steel sheets for deep drawing processes, e.g. DC04, components can also be made of metal with specified strength and chemical resistance properties. One of such materials is titanium sheet. In this paper, FLC for GR1 titanium sheet will be presented. It was obtained by means of a new author’s method named as ALSAD (Analysis of Laser Speckle Activity Differences). So far, applied methods of FLC determination have been mainly based on the measurement of the strain distribution in the area of the created groove, deformation gradient and deformation speed. For this reason, detection of strain localization has been dependent on the strain measurement method. The ALSAD, based on laser speckle phenomenon allows detection of defects initiation on the sample surface independently of the strain distribution measurement and it allows, for example, to relate a moment of defect initiation directly to the sample height or forces occurring in the process. In this paper strain values for strain localization, grooves and cracks for GR1 titanium sheet will be shown. Obtained results show good formability of this material, which was verified by means of 3D digital microscope. Such results allow tracing precisely the formation of the defects starting from strain localization up to the crack appearance, which would be helpful for advanced numerical simulations.