A Finite Element Study On The Mechanism Of High Speed Fragment Injury In The Composite Tissue Of The Pig's Maxillofacial Region

Fragment injury refers to the damage of the structure and function of the body caused by the projectile produced by the explosive weapon when it explode,and it will crush,tear,concussion and transient cavity effect after hitting the body.With the change of modern war mode,the high-speed fragment produced by explosive weapons has become the most important factor in casualties among both combatants and civilians in wars.The previous method of high-speed fragment injury ballistics mainly depends on the bionic tissue and measuring instruments in animals.The limitation lies in the high cost of the experiment,the limited measuring instruments site and direction,the difficulty of data collection,and the dispute of animal ethics.In this experiment,a new type of dynamic loading platform was used,and the standardized fragment was applied to injury the mandibular region of the experimental pig.Dynamic finite element simulation was used to simulate the high-speed fragment injury of pig's mandibular and to simulate the dynamic damage process under different injury conditions.The numerical simulation results were compared with the experimental data of animal experiments to establish a standardized finite element model of maxillofacial high-speed fragment injury,which is scientific,reliable and economical.In this study,a finite element analysis method was used to establish a digital model of high-speed fragment injury and dynamic simulation,and to study its biomechanical characteristics.The computer simulation model is provided for the simulation experiment of high-speed fragment injury.Methods:First of all,we use CT three-dimensional scanning technology to scan the fresh pig head and obtain the original image data of fresh pig head.The data is edited in the MIMICS to precisely select the desired area of the experiment,then we calculated the 3D model of the area.Then,the finite element preprocessing was carried out on the finite element software,the model was solidified and the mesh was divided,and the pig head solidification model was formed.A two stage light gas gun was used to launch the same shape 30 CrMnSi alloy fragment to impact swine mandibular angle area.Biomechanical data such as acceleration at the angle of the mandible and strain on the condyles during collision were measured.The actual damage area and jaw acceleration were measured and compared with the digital simulation results.The right mandibular angle was impacted by the fragment with different velocities in finite element analysis software.The actual damage area and jaw acceleration were measured and compared with the digital simulation results.Results:Experiment 1: In this experiment,we first scanned the fresh pig head by thin layer CT,and used the MIMICS to separate the pig's mandibular tissue in the CT data of the pig head and reconstruct the pig mandibular composite tissue to generate the three-dimensional model of pig mandibular compound tissue.The model size and physical specimens were close to anatomical structure,the model is smooth,no serious distortion,the details are well preserved.Experiment 2: High-speed fragment impacted the mandibular tissue,the fragment left in the tissue.The surface of the soft tissue was a similar circular wound,the diameter is larger than the diameter of the cylindrical fragment,the wound was roughly cylindrical.The accelerometer located in the mandibular angle area did not loosen or fall off.Strain in the condylar neck pasted firmly,without loosening.Wire integrity was good,no breakage or damage.Three-dimensional reconstruction of the mandible showed that the entrance of bone lesions were small and the exit were big,the shape of the entrance and exit are irregular,fragments remain in the contralateral mandibular bone tissue.Experiment 3: The experiment 2 was simulated by finite element software.The collision process is similar to Experiment 2.The fragment with the speed of 831m/s,1120m/s and 1536m/s resulted in the smaller mandibular damage area of entry in the in vivo experiment by 13.4%,23.6% and 22.3%,that of exit by 18.7%,23.0% and 26.5%;the smaller accelaration peak by 16.7%,15.3% and 14.6%.Comparing the acceleration waveform shows that there is still a certain gap between the experimental and the simulation of acceleration peak,but the waveform and the trend fit well.Conclusion:1.The 3D model reconstructed and solided by software has a realistic appearance and clear structure,and improves the modeling speed and modeling accuracy.2.The data of the high-speed fragment injury experiment was measured accurately and objectively,which can lay a solid foundation for the establishment of finite element model of maxillofacial high-speed fragment injury.3.In this study,the soft tissue material was combined with bone tissue during modeling.Experiments simulate the dynamic process of high-speed fragment injury of composite tissue.Experimental compliance is better,authenticity is higher.