X-rays probe the high-strain rate world of magnesium, a major achievement in studies to create new military-grade materials
May 23, 2014
By T'Jae Gibson, ARL Public Affairs Office
Experiments recently conducted by scientists at the U.S. Army Research Laboratory and Johns Hopkins University are providing an "invaluable look" at the processes occurring at crystalline scales in real time and will allow for validation of atomistic and crystalline-level models that are being developed within the ARL Enterprise for Multiscale Research in Materials, and the Materials for Extreme Dynamic Environments Collaborative Research Alliance.
According to Dr. John Beatty, who manages the research alliance, these experiments relied on x-rays produced from the Cornell High Energy Synchrotron Source, or CHESS, and a fast-pixel array x-Ray detector, to peer deep into the crystal plasticity of magnesium at high-strain rates. Data from these experiments rendered temporal resolution at the microsecond scale during a high-strain rate Kolsky bar experiment.
Professor Todd Hufnagel, Johns Hopkins University, designed and led the collaborative execution of these unique "first of their kind" experiments at high-strain rates.
Magnesium has most commonly been used in aircraft and vehicle structural platforms, and lethality applications. Only recently has research incorporated it into studies that aim to develop personal protection equipment or armor applications.
"Since 2006, the U.S. Army has been evaluating magnesium (Mg) alloys for ballistic structural applications. While Mg alloys have been used in military structural applications since World War II, very little research has been done to improve their mediocre ballistic performance. The Army's need for ultra-lightweight armor systems has led to research and development of high-strength, high-ductility Mg alloys," wrote Tyrone Jones, an ARL materials engineer, in a paper he published in 2012.
CHESS is a high-intensity x-ray source supported by the National Science Foundation, which provides users state-of-the-art synchrotron radiation facilities for research in physics, chemistry, biology, and environmental and materials sciences. A synchrotron is an extremely powerful source of x-rays.
"The deformation processes active at high-strain rates include both dislocation glide and twinning, which both affect the x-ray patterns observed in distinct fashions," said Beatty.
"These efforts are at the forefront of ARL's long-term strategy to develop the capability to design materials for protection applications where high-strain rate behavior is critical," said Beatty.
Over 100 experiments were completed this spring, and the work to analyze the voluminous data is now underway within the ARL enterprise.
"At the moment we are analyzing the data to see whether they support current theories about the high-strain rate behavior of magnesium. Going forward we are designing new experiments that will provide even more detailed information about how a wide range of materials deform and fracture under high-rate loading," said Hufnagel.