Measurement of sheet-metal planar Anisotropy at medium strain-rates by digital image correlation
Author(s): R. Tutsch(*), G.B. Broggiato(**), M. Fischer (*), V. Veglianti(**), D. Ferrari(**)
Affiliation(s): (*) Institut für Produktionsmesstechnik, Technische Universität Braunschweig , (**) Dipartimento di Meccanica e Aeronautica, Università di Roma \
Topic: 2. Development of Optical Measurement Systems
A novel test methodology to investigate the strain rate influence on planar and normal anisotropic behavior in thin sheet metals is presented. Dynamic tests at medium strain rate were carried out using an electromechanical material testing machine. To increase the dynamics of the process we developed a specialized clamping system containing a set of preloaded springs. When released, the springs create a tensile pulse on the specimen that is pulled with a strain rate that may reach 100s-1. Spring release is caused by the rupture of a sacrificial specimen, clamped together with the tested one, but differently shaped so that it fails when the other one is still almost undeformed. The specimen surface is prepared with a random speckle pattern by spray-painting. Deformation is measured by digital image correlation of adjacent frames of a digital camera. A high spatial and temporal resolution is reached by applying a high-speed camera with up to 1000 frames/second at 1024 x 1024 pixel. To cope with the huge amount of data the triggering of image acquisition and efficient image processing algorithms are vital. Some results of anisotropy measurement on high-strength alloys are presented.