背景:主动人体模型(AHBM)在动态应用中通过有限元(FE)代码中的主动肌肉桁架元素考虑肌肉骨骼运动和关节刚度。在最新型号中,例如,在THUMS™版本5中,几乎所有人类肌肉群以连接每个关节的一维桁架元件的形式建模。虽然过去已经做了很多工作来改善这种1D肌肉系统的主动和被动行为,根据验尸后人类受试者(PMHS)测试数据,以更简化的方式对THUMS的体积肌肉系统进行建模。迄今为止,对于整个人体模型的体积肌肉系统,几乎没有考虑等距收缩的刚度变化效应。虽然以前的作品考虑了单块肌肉的这一方面,由于体积肌肉的等距收缩而引起的刚度变化对AHBM行为和计算时间的影响尚不清楚。
方法:在本研究中,使用THUMS第5版AM50乘员模型模拟了简化的正面碰撞。为材料模型MAT_SIMPLIFIED_FOAM确定了调节THUMS中固体元素的肌肉组织刚度的关键参数,并为臀部和大腿预定义了不同的刚度状态。
结果:正面碰撞时,肌肉僵硬度的变化对AHBM整体行为有影响,包括预期的损伤结局.大腿和骨盆肌肉僵硬的变化,以及整个人体模型和基于文献数据的应变率相关刚度定义对计算时间没有显着影响。
结论:运动学,峰值冲击力和刚度变化与文献数据基本一致。然而,为了进行比较,必须考虑不同的实验设置,因为这个话题在过去的汽车应用中还没有得到充分的实验研究。因此,本研究对正面碰撞结果的验证存在局限性.
结论:默认THUMS材料模型参数的变化允许在整个AHBM应用中有效改变体积肌肉的硬度。使用这项工作中建议的方法改变肌肉刚度不会影响计算时间。由于缺乏验证数据,这项工作的结果只能在某些限制下进行验证。在未来的工作中,可以用最近发布的模型来代替默认的Thums材料模型,以实现可能更具有生物性的肌肉行为,这甚至允许1D和3D肌肉系统的功能依赖性。然而,这些模型对计算时间和模型稳定性的影响尚不清楚,应在未来的研究中考虑有效的AHBM应用。
BACKGROUND: Active human body models (AHBM) consider musculoskeletal movement and joint stiffness via active muscle truss elements in the finite element (FE) codes in dynamic application. In the latest models, such as THUMS™ Version 5, nearly all human muscle groups are modeled in form of one-dimensional truss elements connecting each joint. While a lot of work has been done to improve the active and passive behavior of this 1D muscle system in the past, the volumetric muscle system of THUMS was modeled in a much more simplified way based on Post Mortem Human Subject (PMHS) test data. The stiffness changing effect of isometric contraction was hardly considered for the volumetric muscle system of whole human body models so far. While previous works considered this aspect for single muscles, the effect of a change in stiffness due to isometric contraction of volumetric muscles on the AHBM behavior and computation time is yet unknown.
METHODS: In this study, a simplified frontal impact using the THUMS Version 5 AM50 occupant model was simulated. Key parameters to regulate muscle tissue stiffness of solid elements in THUMS were identified for the material model MAT_SIMPLIFIED_FOAM and different stiffness states were predefined for the buttock and thigh.
RESULTS: During frontal crash, changes in muscle stiffness had an effect on the overall AHBM behavior including expected injury outcome. Changes in muscle stiffness for the thigh and pelvis, as well as for the entire human body model and for strain-rate-dependent stiffness definitions based on literature data had no significant effect on the computation time.
CONCLUSIONS: Kinematics, peak impact force and stiffness changes were in general compliance with the literature data. However, different experimental setups had to be considered for comparison, as this topic has not been fully investigated experimentally in automotive applications in the past. Therefore, this study has limitations regarding validation of the frontal impact results.
CONCLUSIONS: Variations of default THUMS material model parameters allow an efficient change in stiffness of volumetric muscles for whole AHBM applications. The computation time is unaffected by altering muscle stiffness using the method suggested in this work. Due to a lack of validation data, the results of this work can only be validated with certain limitations. In future works, the default material models of THUMS could be replaced with recently published models to achieve a possibly more biofidelic muscle behavior, which would even allow a functional dependency of the 1D and 3D muscle systems. However, the effect on calculation time and model stability of these models is yet unknown and should be considered in future studies for efficient AHBM applications.