• Jack C Roberts, James V O'Connor, and Emily E Ward.
• Applied Physics Laboratory, a Division of The Johns Hopkins University, Laurel, Maryland 20723-6099, USA. jack.roberts@jhuapl.edu
• J Trauma. 2005 Jun 1; 58 (6): 1241-51.

BackgroundAccording 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 (FEM) to study these effects.MethodsA finite element model (FEM) 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.ResultsUsing 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.ConclusionsThe 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.

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