Army, DOE studies deliver never-before-seen material failures during high-pressure experiments

October 07, 2014

By T'Jae Gibson, Army Research Laboratory, Public Affairs Office

For the first time, U.S. researchers were able to observe and measure the dynamic deflection and failure of material fibers as they deformed under high impact and at high speeds during recent experiments at the Dynamic Compression Sector of the Argonne National Laboratory's Advance Photon Source.

With this information, Army Research Laboratory scientists say researchers will be better able to develop novel armor technologies to improve protection levels for U.S. warfighters.

"If we know at very high fidelity scales how and why an armor or armor material is failing, we may be able to come up with a new material or material response mechanism to circumvent the failure mode and, in turn, significantly increase the armor performance by eliminating this 'weakest link' failure mode," explained Dr. Michael Zellner, an ARL physicist.

ARL is one of four founding members of the Dynamic Compression Sector of Argonne National Laboratory's Advanced Photon Source, or APS, which allows unprecedented research capabilities for the study of high rate dynamic events. Zellner, along with a dozen other scientists and directors, is a board member of the Dynamic Compression Sector Scientific Working Group. That group represents the founding laboratories and guides development of the $25 million sector and the science that occurs there.

As a result of the APS, Zellner said researchers will now be able to increase in spatial and temporal resolution of the diagnostic when attempting to visualize material in situ during a dynamic event.

"This particular facility acquires phase contrast images using X-rays. The data it returns is somewhat comparable to conventional attenuation radiographs, but relies upon an induced phase shift of the x-rays. Not including this diagnostic, current state-of-the-art pulse X-radiographs typically have a temporal resolution of about 80 nanoseconds and a spatial resolution of about 2.5 line pairs per millimeter (or discrimination of a single feature over 400 micrometers). Proton radiography, a type of radiography that uses protons as the scattering medium instead of X-rays, has a temporal resolution of about 60 nanoseconds and a spatial resolution of about 200 micrometers.

"The current technique, which is phase contrast imaging, has a temporal resolution for motion blurring that is less than 50 picoseconds, or about .05 nanoseconds, and a spatial resolution of about 2-3 micrometers. This allows us to study the material response at a new scale, which may lead to advancements in our knowledge of how the material behaves," said Zellner.

The experimental capabilities there are the first-of-its-kind in the world. From its Chicago-based facility, experiments focus on time-resolved x-ray diffraction and imaging measurements in dynamically compressed condensed matter.

ARL's recent experiment examined how a high-performance composite material, much like the material that's used as synthetic ice for ice skating rinks or as a biomaterial for hip or knee implants and even in U.S. military soldier helmets, responds when penetrated. Using a newly implemented gas gun and the Advanced Photon Source synchrotron, a type of cyclic particle accelerator, researchers were able to obtain phase contrast x-ray imaging to characterize materials at the micron scale under dynamic loading and penetration.

He said ARL is still analyzing and "trying to fully understand the data."

"In the first set of data, we are able to quantify the dynamic strength of the fibers in Dyneema, an Ultra-high-molecular-weight polyethylene, and separate fiber strength influences on penetrators from density-driven influences. We were able to do this in two orthogonal views relative to the composite anisotropic structure. A third view is still needed to complete the volumetric response.

During a number of tests, Army researchers were able to identify where and when failure initiated along the fibers when placed under load, and when and where target material failed. He said the team also identified.

"These findings are very important because we can now begin to parameterize models, and begin to develop theories on the material response. This information, along with a complete theory, will inform us on where and when energy is absorbed, which may inform us if we can do a better job of managing it to create greater retardation of penetration, i.e., better armor," said Zellner.

The DCS is benefitting ARL because Argonne National Laboratory (among others) has been working on developing phase contrast imaging for the past few years. DCS adds the component of coupling dynamic loading facilities to the beam line so that we can do phase contrast imaging on penetration type and dynamic loading experiments. This is very complex because coupling a dynamic drive, which has microsecond to millisecond jitter to a technique, which requires approximately 50 picosecond temporal resolution, is not trivial.

This research is a joint effort between ARL, Argonne National Laboratory, and the Los Alamos National Laboratory.

The Advanced Photon Source at Argonne is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy's Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security.

The U.S. Army Research Laboratory of the U.S. Army Research Development and Engineering Command is the Army's corporate laboratory, consisting of more than 1,900 federal employees (nearly 1,300 classified as scientific and engineering) and is headquartered in Adelphi, Maryland. The Laboratory's in-house experts work with academia and industry providing the largest source of world-class integrated research and analysis in the Army. For more information, articles or photos, visit www.arl.army.mil/media.

 

Last Update / Reviewed: October 7, 2014