Shrinking the inside of an explosion

August 30, 2016

WASHINGTON, D.C., Aug. 30, 2016 -- Testing explosions is epic science. The most detailed studies of explosive charges have been conducted at national laboratories using a gun as big as a room to fire a flat bullet -- the flyer plate, typically 100 millimeters in diameter -- into an explosive charge inside a thick-walled chamber that contains the fierce blast. The tests require enormous facilities.

Though cumbersome, the flat plate impact is the only way to precisely recreate the conditions inside a detonating explosive -- and now researchers at the University of Illinois at Urbana-Champaign have recreated this in miniature on a tabletop. In the process, they have made important new contributions to the field of energetic materials by precisely recreating conditions inside a bomb and achieving new levels of accuracy in measuring them.

Their results inform a topic known as the hot spot model of explosive initiation by revealing the dynamics of hot spot growth. That's important because their long-term goal with improved testing is to make safer explosives -- and eliminating hot spots is one way to do that. Their report appears this week in the journal Applied Physics Letters, from AIP Publishing.

Dana D. Dlott, at the University of Illinois at Urbana-Champaign's School of Chemical Sciences and Frederick Seitz Materials Research Laboratory, explains the team's work this way: "Because we can do this so many times a day with a small-scale device on a benchtop that has highly sophisticated optical diagnostics, we see what is happening during the millionth of a second the charge is exploding, with unprecedented accuracy."

He emphasized that their approach does not replace the conventional test methods. Rather, their instrument and small-scale tests contribute to understanding how bombs really behave.

"Our apparatus allows us to look at the fundamental mechanisms of the initial events never before seen," he said.

"This is an important verification of the hot spot model of explosive initiation, and also, it's important because we measured time scales and rates never before seen," added Will P. Bassett a graduate student and member of the research team. Much has been written about hot spots, but they are not often observed and the detailed dynamics of hot spot growth have not been explored before this study.

Hot spots are a hot topic in bomb research because they play a crucial role in the phase cycle of explosions, and in controlling explosions and their aftereffects.

"Depending on the impact duration, the growth spurts could be as fast as 300 nanoseconds and as slow as 13 microseconds," Bassett said.

Their experiments use a pulsed laser to launch a tiny flat bullet 0.5 millimeter in diameter at speeds up to 12 times the speed of sound. This flyer plate impacts an explosive charge that is less than one millionth the size -- it could fit inside an adult's hand -- yet capable of producing precisely the same conditions as in a detonating explosive.

The current work builds on the team's previous research into the complex chemical kinetics of bomb behavior. In it the team observed that the powdered form of a standard test explosive known as HMX material -- a common prototypical test material and most powerful explosive in general use -- explodes in two phases. First, there is an immediate, prompt explosion at impact. Second, a delayed explosion occurs 300 nanoseconds later -- one nanosecond is one-billionth of a second. This new paper extends the work to reveal that initially a small part of the explosive started to react and this spatially limited reaction spread throughout the HMX.

For next steps, the team will continue to validate its instrument and apply test results to improving safety outcomes of explosion science.
The article, "Shock Initiation of Explosives: Temperature Spikes and Growth Spurts," is authored by Will P. Bassett and Dana D. Dlott. The article will appear in the journal Applied Physics Letters on Aug. 30, 2016 [DOI: 10.1063/1.4961619]. After that date, it can be accessed at:


Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See

American Institute of Physics

Related Work Articles from Brightsurf:

Healthy food labels that work and don't work
A Duke-NUS Medical School study finds that new labels may be needed to help consumers make healthier food purchases.

Control over work-life boundaries creates crucial buffer to manage after-hours work stress
Workers with greater boundary control over their work and personal lives were better at creating a stress buffer to prevent them from falling into a negative rumination trap, says a new study co-written by a trio of University of Illinois at Urbana-Champaign experts who study occupational stress and employee well-being.

Can't concentrate at work? This AI system knows why
Computer scientists have developed a way to measure staff comfort and concentration in flexible working spaces using artificial intelligence.

There's a better way to think about being kept waiting at work
Generally, abstract thinking leads to better outcomes, such as more creativity, wider vision and feeling more powerful.

Making light work
A collaboration between McMaster and Harvard researchers has generated a new platform in which light beams communicate with one another through solid matter, establishing the foundation to explore a new form of computing.

Does flexible work 'work' for Aussie parents?
An Australian study examining the relationship between flexibility and parent health has revealed formal family-friendly workplace provisions alone are not meeting the demands of working mothers and fathers.

Do open relationships really work?
Open relationships typically describe couples in which the partners have agreed on sexual activity with someone other than their primary romantic partner, while maintaining the couple bond.

Ebola antibodies at work
Scientists in Israel and Germany show, on the molecular level, how an experimental vaccine offers long-term protection against the disease.

Work that kills
More than 64% of employed Russians work evenings, nights or weekends, and this is one of the highest figures among European countries.

Reattaching to work is just as important as detaching from work, study finds
Employees who mentally reattach to work in the morning are more engaged at work, according to a new study.

Read More: Work News and Work Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to