Findings from a study by a team of USC medical and engineering researchers could lead to a better bulletproof vest and possibly to super strong and “intelligent” armor.

As part of the study, a bullet from a .45-caliber handgun slammed into soft body armor with the same impact as a 90-mile-per-hour fastball whacking a bare chest.

“We studied how it would feel to get shot while wearing armor or bulletproof vests,” said Bart Kosko, a professor of electrical engineering in the USC Viterbi School of Engineering.

The data analysis employed a novel mix of standard statistical methods and more exotic fuzzy-logic techniques.

Fuzzy logic – one of Kosko’s areas of expertise – uses shades of gray rather than simple yes/no answers, allowing humans to program computers with common-sense rules.

“This told us how much injury to expect from a handgun bullet hitting armor,” Kosko said. “Handgun bullets are like baseballs. They do not knock people backwards as in the movies. Instead they bruise soft tissue.”

Kosko teamed with noted medical researcher W. French Anderson, director of the Keck School of Medicine of USC’s Gene Therapy Laboratories, and Ph.D. student Ian Lee of the USC Viterbi School on the paper “Fuzzy Modeling of Gunshot Bruises in Soft Body Armor.”

The paper was published by the 23rd International Conference of the North American Fuzzy Information Processing Society held in June (and co-sponsored by the Institute of Electrical and Electronic Engineers).

Kosko has authored many books on fuzzy logic. Anderson – who won international attention for being the first to cure a genetic defect in a human by transplanting a gene – also authored the forensic analysis of the 1986 FBI Miami firefight. The FBI has approved his report for release to law enforcement officials.

The research began when Anderson posed a simple question: What can science tell us about the bruising and other effects that result when someone gets shot wearing soft body armor? There had been virtually no scientific work on the problem to that point, Anderson said.

“The FBI had asked me to look into this, and I immediately thought of Bart Kosko. Bart is an original thinker, and his ‘fuzzy logic’ sounded perfect for this task,” Anderson said.

The available evidence was scattered and incomplete. The FBI-published statistics showed that no handgun bullets killed armor-clad police officers by piercing. Meanwhile, the military continues to insert so-called trauma plates in a soldier’s flack jacket to stop rifle bullets.

The National Institute of Safety and Technology developed armor-test procedures that used modeling clay to measure backface deformation – the deformation in the armor’s backing material after a gunshot.

But how does a 10-millimeter deformation in clay correspond to damage on a body? The researchers developed a trainable fuzzy system based on data that they obtained from numerous test firings of four different caliber bullets (.22, .38, .40 and .45) into ordnance gelatin-backed vests and other materials. Their analysis was based on bruise patterns from actual shootings.

The backface deformation’s depth and width on the armor estimated the trauma that would have resulted on the body beneath the armor. Timing established the average speed of each box of bullets.

The simplest findings dealt with bullet momentum (mass times velocity) and bullet energy. The energy of a speeding bullet grows with the square of its velocity. But slower moving heavy bullets (like the .45 caliber) bruised more than high velocity lighter ones (like the .22 caliber).

To get a clearer and more intuitive understanding of a bullet's actual impact, the researchers backed the armor against plumbers’ putty, and then compared the impact with that of a baseball hurled by a pitching machine. While a .45 carries the impact of a major league fastball in the ribs, a .22 is equivalent to a hit with a ball going 40 mph, the researchers found.

“This finding can help armor makers improve the tradeoffs involved in making thin, extended-wear armor that minimizes gunshot bruises,” Kosko said. “It can also help give police officers a better sense of what it feels like to be in the literal line of fire.”

“I often make presentations to law enforcement personnel about surviving deadly confrontations, but no one could explain in an understandable way what it feels like to be shot in the chest wearing soft body armor,” Anderson said.

“Finally, we have something. Being hit by a baseball is something we can relate to.”

New developments in lightweight smart materials and nanoscale devices promise super strong armor that can detect approaching bullets, report a wearer’s vital signs and injuries, and then change armor nano-properties to react to threats, said researchers.

For the original paper “Fuzzy Modeling of Gunshot Bruises in Soft Body Armor,” go to: http://sipi.usc.edu/~kosko/NAFIPS-04.J04.pdf.