Modeling the Effect of Non-Penetrating Ballistic Impact As a Means of Detecting Behind Armor Blunt Trauma

Background: According to the National Institute of Justice (NIJ) Standard 0101.04, the maximum deformation a soft armor vest can undergo without penetration is 44 mm. However, this does not take into account the effect of the pressure wave or energy transferred to the organs within the torso due to behind-armor blunt trauma (BABT). Therefore, a study was undertaken to develop a finite element model to study these effects. Methods: A finite element model of the human thorax, complete with musculoskeletal structure and internal organs (heart, liver, lungs, and stomach), intercostal muscle, and skin, has been developed in LS-DYNA. A Kevlar® vest was modeled on the chest to simulate non-penetrating ballistic impact. Results: With use of a projectile modeled with a size and mass equivalent to a 9-mm (124-grain) bullet at 360 and 425 m/s, four impacts were simulated against NIJ level II and level IIIa Kevlar® vests at the midsternum and right thorax. At the same velocity, the pressures decreased by a factor of 3 and the energy absorbed by the organs decreased by a factor of 6 for the NIJ level II and level IIIa vests, respectively. As the projectile velocity increased, the peak pressures increased by a factor of 3 while the energy absorbed by the organs increased by a factor of 4. Conclusion: The resulting pressure profiles and kinetic energy exhibited by the respective organs indicate this model may be useful in identifying mechanisms of injury as well as organs at an elevated injury risk as a result of BABT.