【作者】 李睿；

【导师】 兰惠清； 李志刚；

【作者基本信息】 北京交通大学 ， 载运工具运用工程， 2025， 博士

【摘要】 交通事故、坠落、跌倒、外物撞击等场景所引发的头部碰撞有较高的概率导致儿童的创伤性颅脑损伤。脑挫伤作为低龄儿童主要的颅脑损伤类型,其较高的发生率、致残率和死亡率已严重威胁儿童的生命安全。然而,低龄儿童的脑挫伤特性与成人的差异尚不清晰,另外脑挫伤的耐限尚不明确,这使得低龄儿童在碰撞载荷下对脑挫伤损伤风险的评估受到了较大限制。因此,研究低龄儿童脑挫伤特性并确定相应的耐限值,对车辆碰撞、摔倒跌落等场景下相关儿童保护法规的制定以及儿童头部防护策略的提出具有重要意义。受伦理道德的限制,难以获取儿童尸体样本开展试验研究。本文首先采用国际上广泛认可的以幼龄小猪代替低龄儿童的方法,在头部坠落冲击工况(代表头部碰撞减速场景)和落锤冲击头部工况(代表钝物撞击头部场景)下开展了导致脑挫伤的试验分析;然后建立了具有精细解剖学结构和真实材料属性的小猪头部有限元模型,通过对颅脑多个力学响应数据及脑挫伤区域的试验验证,确定了能够较好表征颅脑力学响应和脑挫伤的头部模型建模策略,并将其应用于低龄儿童头部的建模;接下来基于上述幼龄小猪试验结果和对应的碰撞仿真分析结果共同揭示了低龄儿童脑挫伤特性;最后建立了典型年龄节点低龄儿童头部模型,基于这些模型对儿童头部真实碰撞事故进行了仿真重现,获取了不同事故下儿童脑组织多个力学指标结果,通过引入各个力学指标对应的临界值和权重系数,提出了一种脑挫伤综合评价准则并确定了相应的耐限值。主要工作总结如下:(1)典型碰撞工况下的小猪脑挫伤试验分析。在坠落工况和落锤工况下,分别开展了不同冲击能量的小猪头部碰撞试验(0.4、0.7、1、1.35、1.7和2 m高度下的坠落试验以及8.1、12.7、20.3和21.9 J冲击能量下的落锤试验),采集了碰撞过程中的头部碰撞力和颅内压响应,建立了两种碰撞工况下碰撞力、颅内压与外部冲击能量间的关系,理清了外部碰撞载荷工况、撞击位置对脑挫伤区域、大小等的影响规律。(2)具有精细解剖学结构和真实材料属性的小猪头部模型的建立及验证。通过小猪头部CT/MRI图像获取其头部各部位准确的几何结构,通过脑组织等部位的材料力学实验测定相应的材料特性并进行本构表征,建立了包括脑组织、颅骨、软组织、脑脊液、硬脑膜、软脑膜、下颌骨等详细结构的小猪头部有限元模型。在8个工况(4个坠落工况,3个落锤工况,1个压缩工况)下从头部接触力和颅内压两个方面对模型进行了验证。结果表明,仿真与试验的平均误差均在10%左右,所建立的小猪头部模型具有较高的生物逼真度。该模型的建模策略可用于后文儿童头部模型的建模当中。(3)低龄儿童脑挫伤特性分析。按照导致脑挫伤的试验工况对小猪头部模型进行仿真,通过将试验得到的脑挫伤区域与仿真输出的脑组织多个力学指标结果进行对比确定了能够用于表征脑挫伤的力学指标。结果表明,脑组织的最大主应变、最大剪切应变和颅内压均能够用于表征脑挫伤。进一步综合两种碰撞工况下的试验结果和仿真结果,阐明了低龄儿童脑挫伤特性,即:典型碰撞工况所引发的低龄儿童脑挫伤通常发生在撞击侧的脑组织,表现为冲击伤,其主要是由撞击区域颅骨的弯曲变形导致的。颅骨弯曲变形会使得颅脑间出现相对位移,而较大的颅脑相对位移会导致较高的颅内正压力、较大的脑组织剪切应变和主应变,进而形成脑挫伤。(4)典型年龄节点低龄儿童头部模型的建立及验证。对应小猪脑挫伤试验和仿真结果,重点从网格尺寸、颅脑组织连接方式及本构模型三个方面进行探究,确定了能够较好表征颅脑力学响应和脑挫伤的可用于儿童头部建模的建模策略。在此基础上,建立了具有精细解剖学结构的6月龄儿童头部模型,并将其作为基准模型,通过基于径向基函数的参数化网格变换方法,依次变换得到了具有较为准确形态特征的其他年龄(新生儿、1岁、2岁、3岁和4岁)儿童头部模型。通过将儿童头部模型仿真结果与已有的实验数据和真实事故进行对比,表明基于本文提出的建模策略建立的儿童头部模型能够较好表征头部宏观力学响应和脑挫伤特征。(5)基于事故重现的低龄儿童脑挫伤耐限值的确定。基于MADYMO多体模型和儿童头部有限元模型,对由医院获取的34例低龄儿童头部碰撞真实事故进行了重现,得到了各个事故工况下的脑组织力学响应。提出了一种脑挫伤综合评价准则,通过统计学分析方法评估了综合评价准则对脑挫伤的预测能力,结果表明本文提出的综合评价准则对脑挫伤具有较高的预测准确性。进一步对事故重现结果进行逻辑回归分析,建立了综合评价准则对应的脑挫伤损伤风险曲线,确定了特定损伤概率下的耐限值。其中,10%、25%、50%脑挫伤概率对应的BCC值分别为0.559、0.726和1.011。图133幅,表21个,参考文献187篇。更多还原

【Abstract】 Head impacts resulting from scenarios,including traffic accidents,different-level falls,same-level falls and foreign object impacts,possess a significant probability of inducing traumatic brain injuries(TBIs)in children.Brain contusion,a prevalent TBI among low-age children,exhibits a high incidence rate,disability rate and mortality,and also poses substantial threatens to the lives of low-age children.However,the characteristics of brain contusions in low-age children and their differences from those in adults remain insufficiently elucidated,and the tolerance limits have yet to be determined.This lack of clear understanding hinders the accurate assessment of the risk of brain contusions in low-age children under impact loads.Therefore,exploring the characteristics of brain contusions in low-age children and determining the corresponding limit values are of significant importance for formulating pertinent laws and regulations in scenarios such as vehicle collisions and falls,as well as devising effective child head protection strategies.Given the ethical constraints associated with conducting tests on samples from child cadavers,this thesis employed piglets as surrogates for low-age children,in accordance with internationally recognized method.The impact tests were conducted to induce brain contusions under free-fall drop impact conditions to simulate head impact deceleration conditions,and drop-hammer impact conditions to mimic blunt object impacts.Subsequently,a piglet head model with detailed anatomical structures and realistic material properties was developed.A modeling strategy for child head models that can better characterize cranio-cerebral mechanical responses and brain contusions was identified through the experimental validation of multiple cranio-cerebral mechanical responses and contusion regions.And the modeling strategy was further applied to low-age child heads modeling.Then,the characteristics of brain contusions were elucidated by combining the results of tests on piglets with the corresponding simulations.Finally,head models for the typical-aged child were developed,and the real-world head impact cases were reconstructed based on above models,and results of multiple mechanical metrics of the brain tissue in various cases were collected.In addition,a comprehensive injury criterion for brain contusions was proposed by incorporating the critical values and weighting coefficients of various mechanical metrics,and the corresponding tolerance limits were determined.The main works are summaried as follows:(1)Experimental analysis of brain contusions in piglets under typical head impact conditions.Impact tests utilizing various impact energies were performed under free-fall drop conditions and drop-hammer conditions,including free-fall drop tests at heights of0.4,0.7,1,1.35,1.7,and 2 m,and drop-hammer tests under impact energies of 8.1,12.7,20.3,and 21.9 J,respectively.The data on the impact force and intracranial pressure(ICP)during impacts were collected,and relationships between the impact force,ICP,and impact energy were revealed for both impact conditions.Furthermore,relationships between the external impact loading condition,impact site and contusion location and contusion area were observed and analyzed.(2)Development and validation of a piglet head model with detailed anatomical structures and realistic material properties.The detailed geometrical structures of various parts of the piglet head were obtained from CT/MRI image sets,while the corresponding material properties were determined by mechanical tests on the brain tissue and other head components.Furthermore,the parameters of the corresponding constitutive models were calibrated.A finite element(FE)model of a piglet head was developed,encompassing the brain,skull,soft tissue,cerebrospinal fluid,dura matter,pia matter and mandible.The piglet head FE model underwent thorough validated against experimental data,focusing on the contact force and ICP under eight conditions:four for the free-fall impact condition,three for the drop-hammer impact condition,and one for the compression condition.The results illustrated that the average error between simulations and tests was approximately 10%,attesting to the high bio-fidelity of the piglet head model.It is worth noting that the modeling strategy of the piglet head model can be adopted in the modeling of the child head model in the later part.(3)Investigation of brain contusion characteristics in low-age children.The piglet head model was employed to simulate the impacts based on experimental conditions conducive to brain contusions.Mechanical metrics capable of describing brain contusions were identified by comparing the experimental brain contusions with simulation results of multiple mechanical metrics of the brain tissue.The results showed that maximum principal strain(MPS),maximum shear strain(MSS)and ICP of brain tissue were effective in describing brain contusions.The characteristics of brain contusions in low-age children were elucidated by combining the experimental data with simulation results under the two impact conditions.The summary of the findings is as follows:brain contusions in low-age children commonly predominantly occur in the brain tissue on the impact side,manifesting as coup injuries under typical impact conditions.These contusions are mainly caused by the skull deformation near the impact site.The skull deformation can result in the relative displacement between the skull and brain tissue,and the consequent increased positive ICP,MSS or MPS within the brain tissue can lead to brain contusions.(4)Development and validation of head models of low-age children at typical ages.By comparing experimental and simulation results of piglets,a modeling strategy applicable to child head modeling was determined.This strategy can better characterize cranio-cerebral mechanical responses and brain contusions,and was identified by focusing on three terms of the mesh size,connections between the cranio-cerebral components,and constitutive models of components.Consequently,a FE model of a6-month-old child head with the detailed anatomical structures was developed based on aforementioned modeling strategy.And the head model was employed as the base model to generate other typical-aged child head models with accurate morphological features through the parametric mesh-morphing method based on the radial basis function,including newborns,1,2,3 and 4 years old children.By comparing simulation results of child head models with the existing experimental data and real-world accident cases,it was illustrated that child head models developed based on the modeling strategy proposed in this thesis,which were able to better characterize global mechanical responses of the head and brain contusions.(5)Determination of tolerance limits for brain contusions in low-age children through accident reconstructions.Utilizing MADYMO multi-body models and child head FE models,34 real-world impact accident cases of low-age children obtained from hospitals were reconstructed to collect mechanical responses of the brain tissue.A comprehensive brain contusion criterion was proposed,and its predictive capability of the criterion were assessed by statistical analysis methods.The results indicated that the proposed criterion possessed high predictive accuracy for brain contusions.Furthermore,based on the results of accident reconstructions and logistic regression analysis,the brain contusion risk curve in terms of the comprehensive criterion for low-age children was developed,and tolerance limits corresponding to specific injury probabilities were determined.The BCC values corresponding to 10%,25%,and 50%probability of the brain contusion were 0.559,0.726,and 1.011,respectively.There are 133 figures,21 tables,and 187 references.更多还原