Behavior of Metals During High-Speed Dynamic Compression
Dynamic punch test in a compression SHB apparatus.
Studying the behavior of metals during a high-speed dynamic compression event has always been challenging due to the complex test setup and fast data capture rates required. Utilizing high-speed cameras, the VIC-3D High-Speed system can be used to quantify the surface displacements and strains in three dimensions over the entire field with great precision. Digital image correlation (DIC) has gained widespread popularity over recent years in such high-speed applications due to its high accuracy, flexibility, and ease of use.
Close-up of the dynamic punch experiment.
A dynamic punch test in which three-dimensional Digital Image Correlation (DIC) is used to measure the deformation of the rear surface of a specimen as it being penetrated is carried out by using a large diameter (50 mm) compression Split Hopkinson Bar (SHB) apparatus. Flat, round Ti-6Al-4V disk specimens are attached to the transmitter bar of a compression SHB apparatus and a tungsten carbide punch is attached to the incident bar and positioned such that it is in contact with the disk. During a test, a compression wave is introduced into the incident bar which causes the punch to penetrate into the specimen. The specimen is mounted on a die fixture that is slotted on both sides such that the rear surface of the disk specimen is visible to two high-speed cameras. This provides a stereographic view of the specimen that is used to measure full-field displacement directly on the specimen using three-dimensional DIC. The contact force between the punch and the disk is determined from the wave in the transmitter bar.
Two Photron SA1.1 cameras running at 100,000 frames per second (10μs interval) at 192 pixel by 192 pixel resolution record the rear surface deformation of the disk specimen. The images are processed by commercial Digital Image Correlation (DIC) software (VIC-3D). The amplitude of the incident wave in this experiment is 400 kN. The last DIC image recorded before failure is shown below. Results from tests with punches of various geometries show that the punch geometry greatly influences the punching force and the failure mode. The data is used to construct and validate deformation and failure models.
Gilat, Amos and Jeremy D. Seidt. EPJ Web of Conferences 94, 01005 (2015).
Last DIC image prior to failure (red dot is the failure point).
“We have been using the Correlated Solution system for several years. The system is easy to set up and use, accurate and fast. Tech support is excellent since you can talk directly with the people that have developed the DIC technology.”
-Dr. Amos Gilat, Dynamic Mechanics of Materials Lab, Ohio State University
Images courtesy of Amos Gilat & Jeremy Seidt at Ohio State University.