Session: 06-01-01: Injury and Damage Biomechanics I - Organ and Tissue Injury Biomechanics 1

Paper Number: 141744

141744 - Lung and Liver Injuries in Behind Amor Blunt Trauma: A Finite Element Modeling Study With Different Indenters 

Introduction: Body armor systems are a component of personal protective equipment (PPE) issued to Warfighters and is intended to provide protection from kinetic threats. While designed to prevent penetration of specific threats, body armor is also required to limit risk of blunt injury when a threat is successfully defeated. Behind armor blunt trauma (BABT) is the dynamic load transfer from a kinetic threat, through the armor to the wearer, and may affect the normal function of vital organs in the thoracoabdominal complex. While legacy BABT requirements are uniformly applied, the underlying thoracoabdominal tissues have different injury tolerances. To improve Soldier safety through body armor optimization, regional injury tolerances are needed. Due to the physiological nature of injuries to viscoelastic organs such as the liver, live animals are suitable biological surrogates. Localized impacts can be delivered to the selected live animal model to develop generalized injury criteria by using appropriately designed indenter systems. The indenters’ physical properties can affect the dynamic load transmission to the animal. Before subjecting biological surrogates to BABT scenarios, it is necessary to pursue parametric models to investigate their effects on kinematics, internal load transfer, and injuries. The objectives of this study were to determine the effect of two different indenter designs by simulating BABT impacts to the liver and lung regions using finite element modeling.

Methods: The shape of the first indenter was based on high-speed x-ray images from previous studies that provided dimensions of the maximum backface deformation in hard body armor during a live round impact. The indenter, termed ID1, had the following dimensions: diameter of 100 mm, dome height of 30 mm, and total length of 70 mm. The second indenter was a right circular cylinder, ID2, with the same diameter and a total length of 40 mm. The mass of both indenters was 230 g. Indenters ID3 and ID4 had the same dimensions as ID1 and ID2, respectively, but the mass was reduced to 150 g. All four indenters were used to deliver impacts at two velocities (30 and 60 m/s) to the liver and lung regions using the Global Human Body Model Consortium mid-size male finite element model. Peak rib and lung strains and liver strain energy densities were extracted along with the kinematics of each impact. The potential for organ and skeletal injuries were determined using literature-reported thresholds of 10.8 µJ/mm³ for liver strain energy density, 15.4% for lung strain, and 2.7% for rib strain.

Results: Peak rib strains ranged from 0.4 to 4.8% in lung impacts and 3 to 11% in liver impacts. Peak lung strains ranged from 8 to 25% in lung impacts, and peak liver strain energy densities ranged from 0.8 to 24 µJ/mm³ in liver impacts. The impact kinematics were such that all four indenters contacted the liver and lung regions without any off-axis motions, implying axial loading; however, the dwell times with the two regions were different. Other results will be given in the full-length paper.

Conclusions: The parametric modeling study showed that the indenter shape, velocity, and mass contribute to both types of injuries, albeit dissimilarly. Analysis revealed the importance of rib coverage on organ injuries and increased susceptibility with the high mass indenter. Individual roles of other indenter physical properties on the kinematics of regional tissue engagement and peak strain and strain energy density limits will be discussed. The role of using available live animal injury data obtained with the 230 g ID1 spherical indenter, as applied to other indenters, will be discussed. Experiments can be designed with live animals using appropriate indenter shapes and velocities to develop generalized injury criteria for the two thoraco-abdominal regions.

Presenting Author: Narayan Yoganandan Medical College Of Wisconsin

Presenting Author Biography: Professor and ASME Fellow.

Authors:

Narayan Yoganandan Medical College Of Wisconsin
Karthik Somasundaram Medical College of Wisconsin
Balaji Harinathan Medical College of Wisconsin
Karthik Banurekha Devaraj Medical College of Wisconsin
Alok Shah Medical College of Wisconsin
Jared Koser Medical College of Wisconsin
Brian Stemper Medical College of Wisconsin
V. Carol Chancey U.S. Army Aeromedical Research Laboratory
B. Joseph McEntire U.S. Army Aeromedical Research Laboratory,