Identification of the Dynamic Tensile Behavior of Geomaterials Based on the Virtual Fields Method and a New Generation-Ultra-High-Speed Camera

摘要

Dynamic behavior of a granite rock was investigated by using the spalling test method. This technique, based on the use of a Hopkinson bar, allows applying a tensile loading at high strain-rates, from a few tens to two hundreds of 1/s, to geomaterials to characterize their dynamic tensile strength. However, the standard 'Novikov' processing method providing the spall strength is based on basic assumptions (linear-elastic behavior until the peak). In addition, the post-peak behavior and the kinetics of damage in the material remain unknown. The use of full-field measurement appears to be of great interest to improve the processing method and to obtain more information from the spalling tests. A new generation ultra-high speed (UHS) camera (Kirana, Specialized Imaging) was used in association with a digital image correlation (DIC) technique to measure the displacement field. Image acquisition was performed at 1,000,000 fps with a resolution close to 800,000 pixels. Dynamic tensile strength was characterized by post-processing DIC measurements with the virtual fields method (VFM) as proposed by Pierron and Forquin (2012). The interest of using the Kirana camera allowing higher spatial resolution compared to previous model of UHS camera (HPV1 ultra-high speed camera is discussed in the present paper).