Numerical Simulation Of The Mechanical Response Of Chest Blunt Ballistic Impact Inducing Indirect Brain Injury

Blunt ballistic impact is defined as bullets, fragments and other projectiles hitting atarget without penetration. In local conflicts and counterterrorism operations, theparticipants were generally equipped with personal protection. The incidence of BABT(Behind Armor Blunt Trauma) caused by blunt ballistic impact has been increasing. Thestudy found that the blunt ballistic impact on chest resulted in not only severe thoracic blunttrauma, but also damage of brain structure and function, which is relevant to thepropagation of chest mechanical loads in vivo. There are three pathways between chest andbrain for mechanical load to transfer, namely: vascular/blood pathway, vertebrae pathwaysand subcutaneous pathways, and vascular/blood pathway was the most direct pathway.However, knowledge about the transmission pathway through which the thoracic impulsiveloads produce effects on the brain and the transmission characteristics of the pathway isunclear. The acquisition of the mechanical responses in thoracic organs and cardiovascularvessels is necessary for the investigation of the BABT. On account of the limitations ofmechanical testing in vivo, the computer modeling and numerical simulation techniqueswere used to calculate the stress and pressure responses in the chambers of heart andcardiovascular vessels. This research could provide a numerical method of illustrating themechanics response characteristics of blunt chest ballistic impact and the theory basis forthe vascular/blood pathway leading to indirect brain injury.In our study，a three-dimensional finite element model of human chest and a localvascular network were developed based on CVH (Chinese Visible Human) data sets byusing the Mimics, Geomagic, HyperMesh and other software. In the LS-Dyna softwareenvironment, a finite element numerical simulation was performed for the dynamicresponse to the blunt ballistic impact, which was caused by a5.56-mm rifle bulletmoving with the speed of910m/s toward a human torso wearing a composite body armorvest. Whereafter, the stress and pressure response of the upper chamber circulation systemwas calculated. Finally, the models and numerical simulation results were validated with animal experiments.The main work and conclusions of the paper included the following aspects:1. A three-dimensional finite element model of human chest was constructed, whichcontains the chest skin, muscles, bones (including sternum, cartilage, ribs, spine), lungs,heart and surrounding structures (including the heart, the left ventricle, left atrium, rightventricle, the right atrium, the ascending aorta, superior vena cava and inferior vena cava).The model could meet the need of the simulation of chest blunt ballistic impact.2. The composite armor plate and5.56mm rifle model was plus to the finite elementmodel of the human chest to perform the simulation of blunt ballistic impact to the chestand calculate the stress distribution in the chambers of the heart as well as the pressure atthe connection of the ascending aorta, superior vena cava with the heart.3. A three-dimensional finite element model of local vascular network (including theascending aorta, aortic arch, carotid artery, subclavian artery, internal carotid artery andexternal carotid artery) was constructed, which set ascending aortic pressure wave at theentrance as the input load. The pressure wave propagation in the upper chamber circulationsystem was simulated to calculate the pressure response on the outlet of the internal carotidartery connected to blood vessel of brain. The pressure wave peaks at the outlet of the leftand right internal carotid artery were35.4KPa and32.5KPa respectively. These data couldcontribute to the prediction of brain injury.4. The same ballistic blunt impact loads was applied as numerical simulation acting onthe test animals to obtain the pressure response with sensor placed in left common carotidartery and the cranial cavity of animals. The pressure wave peaks were78.9KPaå'Œ44.0KPa.Test data and numerical results were consistent, which showed that the model andnumerical results were reasonable. The finite element models developed in this study couldprovide a new approach to the investigation on the mechanism of BABT, and the evaluationand improvement of personal protective equipment.