基于人体有限元模型的汽车前碰撞中驾驶员下肢损伤生物力学研究

发布时间：2018-09-14 14:43

【摘要】：随着安全带配带率的提升及安全气囊在汽车中的普遍使用，乘员头部及胸部在交通事故中受到严重损伤的比例持续降低。美国NASS/CDS的1993－2001年事故统计结果显示，在前碰撞所有AIS2+损伤中，下肢占36%，损失的生命年（LLI）所占比率达到了46%，下肢损伤已超过头、胸部成为事故中受到中等程度及以上（AIS2+）损伤风险最大的部位。下肢损伤一般不是交通事故中导致乘员死亡的直接因素，但其恢复期较长、且会导致巨大的伤痛、下肢生理机能丧失甚至残疾，是汽车碰撞安全研究中不容忽视的问题。为了更好地分析乘员下肢在前碰撞中的损伤机理及耐受限值，本文基于一名中等身材的成年男性下肢解剖学结构，使用软件Hyperworks11.0建立起一个能较好反映下肢生理学特征的坐姿下肢有限元模型，模型包含骨骼（骨盆、骶骨、股骨、髌骨、胫/腓骨、足部骨骼）及软组织（肌肉、皮肤、关节囊、关节软骨、韧带、肌腱）。建立后的下肢模型含有97个部件，单元总数为65,626。其中实体单元为40,155，壳体单元25,263，弹簧单元208个。通过与9组经典的尸体实验结果对比验证，表明下肢有限元模型建模方法正确、材料选用合理，，具有较好的生物逼真度，可用于后续的乘员下肢损伤机理及损伤预测研究中。基于建立的乘员下肢模型，文中开展了一系列前碰撞载荷条件下的车内乘员下肢损伤生物力学研究，包括：股骨在受到膝部轴向压力-外部弯矩时的损伤机理、耐受限值研究；乘员下肢受膝垫碰撞力作用时不同髋关节姿态对骨盆损伤的影响分析；足/踝部在乘员舱侵入条件下的损伤机理及防护参数研究。最后，结合整车有限元模型进行了不同重叠率前碰撞下的下肢损伤对比分析。在建立下肢模型基础上，本文就股骨生理特性对其耐受限值的影响进行分析。在之后开展的外部弯矩对股骨耐受限值影响研究中，本文使用曲梁力学模型及有限元虚拟实验分析了股骨分别受到膝部轴向压力-股骨髁弯矩及膝部轴向力-股骨干横向冲击弯矩两种形式载荷时的损伤机理及耐受限值。结果表明：外部弯矩载荷不仅会影响到股骨的失效部位，而且会影响到股骨的耐受限值。在6组受轴向力-股骨髁弯矩载荷的虚拟试验中，预加轴向力为8.0kN及以上时，失效部位发生股骨颈部，其失效截面弯矩为285Nm~295Nm，而预加轴向力为0-6kN时，失效位置在距股骨末端134.9~171mm的股骨干区域，其失效截面弯矩为381Nm~443Nm；在受轴向力-股骨干横向冲击载荷的虚拟试验中，载荷为8.0kN-0.64kN及8.9kN-0kN时，失效同样发生股骨颈部，其失效截面弯矩为307.2Nm和296Nm；而预加轴向力为0-6kN时，股骨中截面骨折，失效弯矩为382Nm~400.7Nm。研究结果解释了膝部轴向冲击实验中股骨失效全发生在颈部，而前碰撞事故中却有大量股骨干骨折发生时轴向力比损伤准则(10kN)中小的现象。基于下肢模型，本文进行了不同的髋关节屈曲角及展角下的膝部轴向力冲击虚拟试验研究。结果表明：由于髋臼壁各受力点强度不同，膝部轴向冲击下的髋关节姿态会直接影响到骨盆骨折部位及失效值。随着髋关节屈曲角及展角的增大，损伤部位由髂骨转移到髋臼。骨盆失效值随屈曲角的增加而增大13.5%~34.4%，但其失效值随展角的增加先增大后减小，且变化范围为6.0%~20.9%。足/踝部是前碰撞中下肢最容易受到损伤的部位，结合下肢有限元模型，先建立并验证了奇瑞某车型的驾驶员-约束系统有限元模型。然后对前碰撞中引起足/踝部损伤的仪表台设计角度、踏板的向后和向上侵入量、踏板内/外翻角度及踏板的背屈翻转角度五组参数进行了16组正交实验分析。结果表明：其中11组实验产生了小腿或足/髁部的损伤；对胫骨轴向力最敏感的参数是踏板向上侵入量；胫骨合成弯矩和胫骨指数最敏感的参数是踏板向后侵入量；踏板背屈转角及踏板后移量的增大会引起到踝关节最大背屈角的增加；在一定范围内，膝垫夹角越大，越有助于减小因背屈引起的踝关节损伤。对实验结果进行深入分析还发现：胫骨指数与踝关节的损伤没有必然联系，而背屈及内/外翻转角超过了踝关节的生理活动范围是引起踝关节损伤的直接原因。为研究不同重叠率前碰撞中驾驶员下肢的损伤特点，首先对奇瑞公司某有限元整车模型进行了验证；然后使用其进行全宽正面碰撞、40%及25%偏置碰撞的模拟，并总结了三种重叠率前碰撞形式下的整车耐撞性特点；最后分别提取三种碰撞形式下的乘员舱侵入情况及整车加速度作为初始边界条件，结合已建立的驾驶员-约束系统模型开展了三种前碰撞形式的下肢损伤研究。结果显示：由于重叠率不同，整车加速度、乘员舱侵入部位及大小都有较大差别，重叠率越小，则侵入量越大，平均加速度则越小；不同的碰撞特征造成了不同的下肢损伤特点：在25%偏置碰撞中，巨大的膝垫及踏板侵入引起了左侧股骨颈骨折和双侧踝关节损伤；在100%正面碰撞中也产生了右侧踝关节损伤，而40%偏置碰撞中无下肢损伤。进一步分析表明：下肢的损伤风险与整车碰撞加速度波形直接相关；乘员舱侵入量与足/踝损伤并不是线性关系；同等侵入量下，加速踏板比歇脚踏板更容易造成踝关节背屈的后距胫韧带失效及距骨骨折损伤。综上所述，文中建立的下肢有限元模型可作为乘员下肢损伤生物力学研究的有效工具。而使用该模型进行的股骨、骨盆、足/踝部损伤机理、耐受限值及损伤防护的研究结果为前碰撞载荷下的驾驶员下肢损伤防护设计提供了有益的参考。
[Abstract]:With the increase of seat belt allocation rate and the widespread use of airbags in automobiles, the proportion of serious head and chest injuries in traffic accidents continues to decrease. According to the accident statistics of NASS/CDS from 1993 to 2001, 36% of all AIS2 + injuries were caused by pre-collision, and 36% of all AIS2 + injuries were caused by lower limbs, and the proportion of lost life years (LLI) reached a high level. Lower limb injury is not a direct cause of death in traffic accidents, but it has a long recovery period, and can cause great pain, loss of lower limb physiological function and even disability. It is a vehicle crash safety research. We should not neglect the problems.
In order to better analyze the injury mechanism and tolerance limit of the occupant's lower limbs during anterior collision, a finite element model of sitting lower limbs was established based on the anatomical structure of the lower limbs of a middle-sized adult male. The model was composed of skeleton (pelvis, sacrum, femur, patella) and HyperWorks 11.0. Bone, tibia/fibula, foot bones, and soft tissues (muscle, skin, capsule, articular cartilage, ligament, tendon). The established lower limb model contains 97 parts, with a total number of units of 65,626. Among them, solid units are 40,155, shell units 25,263, and spring units 208. The modeling method is correct, the material selection is reasonable, and the model has good biological fidelity, which can be used in the follow-up study of lower limb injury mechanism and injury prediction.
Based on the passenger lower limb model, a series of biomechanical studies on the lower limb injuries of in-car passengers under the condition of anterior collision load were carried out, including: the injury mechanism of femur under axial pressure and external bending moment of knee, the tolerance limit; the pelvic injuries caused by different hip joint postures when the lower limb was subjected to knee pad impact force The impact analysis; the foot/ankle injury mechanism and protective parameters under the condition of occupant cabin invasion. Finally, combined with the vehicle finite element model, the comparative analysis of lower limb injury under different overlap rate of anterior collision was carried out.
Based on the establishment of the lower limb model, the effect of femoral physiological characteristics on the femoral tolerance limit was analyzed. In the subsequent study of the influence of external bending moments on the femoral tolerance limit, curved beam mechanics model and finite element virtual experiment were used to analyze the femur subjected to knee axial pressure-femoral condyle bending moment and knee axial force-femoral condyle axial force respectively. Damage mechanism and tolerance limits of femoral shaft under transverse impact bending moments were studied. The results showed that external bending moments not only affected the failure site of femur, but also the tolerance limit of femur. The failure cross-section moment of femoral neck was 285 Nm~295 Nm, and the failure position was 134.9~171 mm from the end of femur when the axial force was 0-6 kN. The failure cross-section moment of femoral neck was 381 Nm~443 Nm when the axial force was 0-0.64 kN and 8.9 kN-0 kN in the virtual test under the axial force-transverse impact load. The failure cross-section moment of the femoral neck was 307.2 Nm and 296 Nm, while the failure cross-section moment was 382 Nm ~ 400.7 Nm when the axial force was 0-6 kN. The results explained that the failure of the femur occurred in the neck during the knee axial impact test, but the axial force ratio of the femoral shaft fracture in the anterior impact accident was more accurate than that of the injury. (10kN) medium and small phenomena.
Based on the lower limb model, the virtual impact tests of knee axial force under different hip flexion angles and abduction angles were carried out. The results show that the hip joint posture under axial impact of knee has a direct impact on the position and failure value of pelvic fracture due to the strength of each force point on the acetabular wall. The pelvic failure value increased by 13.5%~34.4% with the increase of flexion angle, but it increased first and then decreased with the increase of flexion angle, and the range of change was 6.0%~20.9%.
The foot/ankle is the most vulnerable part of the lower limb in the fore-impact. Combining with the finite element model of the lower limb, the driver-restraint system finite element model of a Chery model is established and validated. Sixteen orthogonal experiments were carried out to analyze the five parameters of the plate's back-bending angle.The results showed that 11 groups of experiments produced leg or foot/condyle injuries.The most sensitive parameter to the tibial axial force was the upward invasion of the pedal.The most sensitive parameters to tibial synthetic bending moment and tibial index were the backward invasion of the pedal. Increasing the angle and pedal displacement will increase the maximum ankle dorsiflexion angle; in a certain range, the greater the knee pad angle, the more conducive to reducing the ankle injury caused by back flexion. The physiological range of ankle joint is the direct cause of ankle injury.
In order to study the characteristics of driver's lower limb injury in different overlap rate pre-collision, a finite element vehicle model of Chery Company was validated firstly, then the full-width frontal impact, 40% and 25% offset impact were simulated, and the crashworthiness characteristics of the vehicle under three overlap rate pre-collision forms were summarized. The results show that, due to the different overlap rate, the acceleration of the whole vehicle, the location and size of the occupant compartment are different, and the overlap rate is smaller. The greater the amount of invasion, the smaller the average acceleration; different collision characteristics caused different characteristics of lower limb injury: in 25% offset collision, the huge knee pad and pedal invasion caused left femoral neck fracture and bilateral ankle injury; in 100% frontal collision, the right ankle injury was also produced, while in 40% offset collision there was no lower limb injury. Limb injury. Further analysis showed that the risk of lower limb injury was directly related to the acceleration waveform of vehicle crash; occupant cabin invasion was not linear with foot/ankle injury; acceleration pedal was more likely to cause posterior tibial ligament failure and talus fracture injury than rest pedal under the same amount of invasion.
In conclusion, the finite element model of the lower limb established in this paper can be used as an effective tool for the biomechanical study of lower limb injuries in passengers.
【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：U467.14;R641

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