Study On The Biomechanical Response And Blunt Injury Mechanisms Of Cardiovascular System In Vehicle Occupants

Studies on the injury mechanism of occupants in automobile collisions contribute to protecting life,reducing traffic accident loss,and improving vehicle product development levels.According to statistics,the rupture of the heart and blood vessels caused by the blunt thoracic impact is one of the main causes of occupant death.At present,most of the research on chest blunt injury focused on rib fracture and thoracic deformation,while the analysis of the injury of internal organs especially the cardiovascular system is less.The heart and vessels are full of blood,and the blood’s pressure and velocity change during a cardiac cycle.Injury studies of the cardiovascular system based on biomechanics involve the coupling of multiple physical fields under severe boundaries and the difficulty of digital modeling of physiological characteristics of the human body,so there are few achievements at present.In this study,a refined biomechanical model of the cardiovascular system was established based on the anatomical structure.According to the contact characteristics of blood and cardiac vascular valve structures,the grid-based method,fluid cavity,and smoothed particle hydrodynamics were used for coupling.Moreover,the study simulated various physiological states of the cardiovascular system,to further analyze the mechanism of blunt injury to the occupant’s cardiovascular system.The effect of blood flow on the blunt injury of the cardiovascular system was studied.Firstly,a finite element model of the aorta was established and the material properties were given according to the uniaxial tensile test results of the porcine aorta.Then,the strain of the aorta with/without blood filling under impact load was analyzed.The results showed that when the aorta model was not filled with blood,the movement and morphology of the aorta did not conform to the real situation,and the location of blunt rupture of the aorta was different from the clinical results.When the aorta model was filled with blood,the simulation can reproduce the typical injury characteristics of the aortic isthmus rupture.Therefore,the simulation of blood is indispensable in the follow-up study on the blunt injury mechanism of the cardiovascular system.The models of the heart and aorta were established by human medical images,and the aortic valve model was established by the artificial valve design method.The relationship between the myocardium and the blood is similar to a container filled with fluid.Then,the fluid-structure interaction between blood and heart is simulated by the method of surface-based fluid cavity.The heart valves are enclosed in the blood,and the movement of the valve greatly affects the boundary of the fluid domain.Thus,smoothed particle dynamics method was used to simulate the coupling between valves and blood.The developed cardiovascular system model was assembled with the occupant model established early,and then subjected to the thoracic impact.The simulation results are compared with the experimental results to verify the validity of the model.The physiological characteristics of the heart were simulated by different blood pressure and valve states.Then the heart with various states was subjected to thoracic impact to investigate the effect of cardiac cycle on blunt heart injury.The results showed that the myocardial injury risk was directly related to the valve state of opening or closing at the time of impact.When the heart is impacted during the ventricular filling period,the myocardium produced higher stress and related higher injury risk.The injury risk of the aortic valve was also related to its state at the moment of impact.When the heart is subjected to the impact at the end of the diastole(aortic valve closed),the blood pressure difference between the two sides of the valve can easily damage the valve.Finally,the human model containing the cardiovascular system was placed into a car to study the response of the heart and aorta under door/steering wheel-to-thorax impact.The results showed that the smaller the angle between the steering disc plane and vertical direction,the larger the peak of blood pressure in the heart and the peak of stress in the myocardium,resulting in a higher risk of injury to both myocardium and valve.In addition,the injury mechanisms of aortic rupture under frontal impact and left/right impact were also studied.In the frontal impact,the compression of the sternum and spine on the aorta was the main cause of the aortic rupture.In left-side impact,the aortic arch is twisted during the impact and makes isthmus injury.In right-side impact,the aortic isthmus was severely stretched and thus rupture.Based on the human anatomy and physiology principles,combined with biomechanical fluid dynamics and other methods,this study established and verified the cardiovascular system model with blood flow and cardiac cycle.The effect of the cardiac cycle on chest collision injury was studied,which provides more comprehensive and reliable results for the mechanism analysis,prediction,and evaluation of chest injury.The modeling and research method can also be used for the injury analysis of other tissues and organs,which improves the application level of biomechanical methods in the occupant injury simulations.