【作者】 陈渝斌；

【导师】 谭颖徽；

【作者基本信息】 第三军医大学 ， 外科学， 2010， 博士

【摘要】 颌面部是人体的暴露部位,战时防护薄弱,平时是暴力、自伤的重点部位,在全身各部位的火器伤中,颌面部火器伤占有较大比例。无论平战时,颌面部火器伤创伤弹道学研究都是全身创伤弹道学研究中的重点问题之一。由于动物模型无法直观动态地观察到模型内部的致伤过程,加上颌面部解剖结构精细、组织器官生物力学性质相差大,无法采用人工材料进行模拟,所以颌面部火器伤的研究中,尚无可以用于致伤过程中生物力学机制研究的模型,这也是目前相关研究的瓶颈之一。有限元法又称有限元素法(Finite Element Method,FEM)或有限元分析法(Finite Element Analysis,FEA),是20世纪50年代末60年代初兴起的应用数学、现代力学及计算机科学相互渗透、综合利用的边缘科学。有限元法的原理是把整个结构看作由有限个细小单元相互连接而成的几何实体,每个单元的力学特征的总装效果反映出结构的整体力学特性,是解决复杂工程学问题的必备工具之一,目前已广泛应用于生物力学研究中。火器伤致伤机理是投射物与机体二者相互作用的物理、病理和解剖的复杂变化过程,其实质是投射物与机体组织之间的生物力学作用及效应。有限元法能够分析物体间及物体内部的复杂力学过程,预测力学作用的效应(如模型的形状、温度等改变),并且可以在电脑上直观显示或输出量化的计算结果以供分析,具有可重复性好、节约实验成本、实验条件容易控制等优点,可弥补目前火器伤模型在致伤过程生物力学机制研究中的不足。因此,将有限元方法运用于颌面部火器伤研究中,有助于颌面部火器伤致伤机理的深入研究,能为颌面部火器伤诊断、救治、防护及投射物致伤效应评估提供新的工具和思路。针对目前颌面部火器伤研究中动物、尸体及人工材料模型在致伤生物力学机制研究中的不足,本研究建立了猪下颌骨火器伤三维有限元模型,通过动物实验验证所采用有限元方法的合理性;用有限元方法仿真不同力学载荷、边界条件下投射物侵彻猪下颌骨的过程,对下颌骨火器伤的生物力学机制进行了初步探讨。研究方法和结果:1.将猪下颌骨计算机X射线断层扫描(computed tomography,CT)数据导入MIMICS软件,经过三维图像重建、实体模型重建后得到猪下颌骨面网格模型;将猪下颌骨面网格模型导入ANSA软件,采用六面体网格与四面体网格结合的方式建立猪下颌骨火器伤三维有限元模型。建立的猪下颌骨三维有限元模型的单元数为674863,节点数为261997,所有单元均为实体单元。结果表明:该模型网格划分合理,单元质量好,与真实标本的几何外形相似程度高,细节损失小;采用四面体单元与六面体单元结合方式建立猪下颌骨三维有限元模型,降低了建模成本,同时兼顾了计算效率和计算精度,能够满足下颌骨火器伤生物力学机制研究的需要。2.通过改良猪下颌骨火器伤动物实验模型,用不同射速、不同形状投射物致伤猪下颌骨标本的下颌角部位,测量各种致伤参数及致伤过程中猪下颌骨的生物力学参数,为分析下颌骨火器伤生物力学机制和验证有限元模型提供可靠的数据。结果表明:实验方法合理,重复性好,测量到的数据具有代表性。3.通过选择适合的材料模型、生物力学参数及接触算法,加载与动物实验相似的力学载荷和边界条件,用所建立的猪下颌骨火器伤三维有限元模型在LS-DYNA软件中进行仿真计算;通过比较有限元仿真结果与动物实验中的实测数据,验证所采用的有限元方法的合理性。结果表明,本研究所采用的有限元方法合理、可靠,对下颌骨火器伤生物力学作用机制及其效应有较好的预测能力,能满足深入研究下颌骨火器伤生物力学机制的要求。4.利用经过验证的有限元模型及仿真方法,加载不同力学载荷、边界条件,进行了不同形状、不同速度投射物侵彻猪下颌骨过程的有限元仿真;从不同角度观察并分析投射物侵彻猪下颌骨的有限元仿真结果,结合本研究动物实验结果及既往文献资料,对下颌骨火器伤的生物力学机制进行了初步探讨。结果表明:骨组织损伤除了与投射物的物理特性(飞行速度、飞行状态、形状及质量等)有关,还和投射物与骨组织间、骨组织与骨组织间的生物力学作用有关,后两者是导致入口及出口损伤范围差异的主要原因;下颌骨损伤的严重程度与骨组织应变率相关;所采用的有限元方法能合理解释投射物侵彻下颌骨过程中部分生物力学机制。5.本研究采用无网格法与有限元法联合建立猪下颌软硬组织复合体模型并进行相关仿真,初步探讨有无网格法仿真肌肉组织火器伤,部分仿真结果与致伤条件相似的动物实验结果接近,说明无网格法在肌肉组织火器伤仿真中有较好的应用前景。结论:1.成功建立了猪下颌骨火器伤三维有限元模型,验证了所建模型及所采用的有限元分析方法的合理性和可靠性。明确了在研究火器伤生物力学机制方面,有限元方法可以弥补目前火器伤研究模型的不足。2.投射物侵彻下颌骨过程中,骨组织损伤除了与投射物的物理特性有关,还和投射物与骨组织间、骨组织与骨组织间的生物力学作用有关,后两者是导致入口及出口损伤范围差异的主要原因。3.投射物侵彻下颌骨过程中,应变率的大小及持续时间可以作为判断和评价骨组织损伤严重程度的标准之一,也可以作为有限元仿真过程中预测骨组织损伤的指标。4.投射物侵彻下颌角过程中,下颌骨损伤主要集中在弹孔周围及弹孔至下颌骨下缘间区域,单纯的下颌角火器伤伴发其他部位下颌骨骨折的可能性较小。5.下颌角部火器伤伴发颅脑损伤时,骨应力传导不是导致颅脑损伤的主要因素。6.无网格法在肌肉组织火器伤仿真中有较好的应用前景。更多还原

【Abstract】 As an exposed part of human body, the maxillofacial region is more susceptible to kinds of firearm-related injuries. The firearm-related injuries of the maxillofacial region have a much higher ratio than the other parts of human body, either in war or peace time. So, it is important to find out the biomechanical mechanism and basic principles of wound ballistics of the maxillofacial region, for clinical, forensic and military purposes. However, due to the difficulty of reproducing the complex anatomical structures of the maxillofacial region by using animal or synthetic material models, the dynamic interactions between projectiles and facial tissues have not been extensively researched.Being an effective mathematical method for solving complex mechanical problems with complicated geometries, the finite element method (FEM) is widely used in study of biomechanical mechanisms. FEM can provide an“insight view”of the interaction processes and clarify transient dynamic mechanisms between the projectile and tissues. It may offer the possibility to precisely measure the amount of energy or force delivered to the tissues, which may correlate with the degree or patterns of biological tissue injury. Moreover, FEM has the advantages of good repeatability, low cost and manageable load conditions, which makes up for the insufficiency of human cadavers, animal and synthetic material models.In this study, a finite element (FE) model of the pig mandible was developed to simulate ballistic impact, and experimental studies were carried out to validate the FE model. Based on the simulation results of FEM, the biomechanical mechanism of wound ballistics of the mandible was investigated and discussed. The main methods and conclusions were as follows:Methods and Results:ⅠComputed tomography (CT) data of the pig mandible was imported into MIMICS software. A three-dimension computer-aided design (CAD) model of the pig mandible was reconstructed by using certain functions of MIMICS. Then, the original triangular surface mesh model of the pig mandible was generated by the“remesh”module of MIMICS. Based on the surface model of the pig mandible, a combined hexahedral-tetrahedral FE model of the pig mandible was developed by ANSA software. The results showed that the number of the elements and node were 674863 and 261997 respectively, and all the elements were solid elements. The FE model of the pig mandible was similar to its anatomical structure. With lower cost of modeling, the combined hexahedral-tetrahedral FE model of the pig mandible can meet the demand of biomechanical research of wound ballistics of the pig mandible.ⅡBased on the improved animal model of wound ballistics of the pig mandible, an experimental study was carried out to measure impact load parameters from the pig mandibles that were shot at the mandibular angle by a standard 7.62 mm M43 bullet or 6.3 mm steel ball. The experimental results showed that the data were reliable and representative. The improved animal model of wound ballistics of the pig mandible was reasonable and repeatable. The results of the experimental study can be used to validate the FE model.ⅢBy chosing appropriate constitutive model, biomechanical parameters and contact algorithm for the FE model of the pig mandible, finite element analysis (FEA) was performed through the LS-DYNA code under impact loads similar to those obtained from the experimental study. The FEM of simulation of wound ballistics of the pig mandible was validated based on the results of comparison between the results of FEA and experimental study. The results showed that the constitutive model, contact algorithm and the parameters, which were chosen for the FE model of pig mandible in our study, were reasonable and reliable. The FEM utilized in our study had a fairly capability of predicting on wound ballistics of the pig mandible.ⅣBy using the validated FEM utilized in our study, FEA was made under different loads and boundary conditions, including different velocities and shape of projectiles. Based on the results of comparison of the output data of FEA among different velocities and shape of projectiles, the biomechanical mechanism of wound ballistics of the mandible was investigated and certain conclusion was drawn.ⅤBy using the element free Galerkin (EFG) method, the process of muscle tissue penetrated by a 7.62mm bullet was simulated. The results showed that the EFG method can meet the need of simulation of penetrating wound of muscle tissue.Conclusions:ⅠWhen concerned with the investigation of biomechanical mechanism of wound ballistics, FEM can make up for the insufficiency of human cadavers, animal and synthetic material models.ⅡDuring the process of penetration, besides the physical characteristics of projectiles, the biomechanical mechanism between the projectiles and bone tissue and the interactive force among bone tissue can play an important role in the difference between the surface area of entrance and exit.ⅢDuring the process of penetration, strain rate of bone tissue can be used to predict and evaluate the severity of damage of bone tissue, both in terms of FEA and experimental study.ⅣWhen the mandible was penetrated by projectiles at mandibular angle, besides the damage of penetrated region, there was little possibility for associated fracture to other regions of mandible.ⅤBony stress conducted from the mandible was not the main factor of the brain injury associated with the penetrating injuriy of mandibular angle.ⅥThe EFG method can meet the need of simulation of penetrating wound of muscle tissue.更多还原