| The lower limb injury caused by under-foot impact loads is one of the most common injury regions in a human body whether in sports activities,automobile frontal collisions,or military actions like trauma caused by anti-vehicular land mines.Among lower limb injuries,ankle injuries generally lead to long-term injuries.Due to restrictions such as ethical and moral constraints,and experimental risks of human volunteers,finite element human models are often developed to explore the mechanism of human body injuries and limits of tolerance under various impact loads,as well as to evaluate and improve the effectiveness of corresponding protective devices.Although several lower limbs and ankle-foot injury prediction models have been established,the models’ validations were very limited,and the reliability and authenticity of injury prediction are rarely considered under different impact velocities.On the other hand,most of the previous model validations were focused on ankle neutral positions,while other postures were not considered.Thus,the objective of the present study is to optimize and comprehensively validate a foot-ankle-leg model,and use it to investigate lower leg injury responses in different under-foot loading environments to provide a theoretical basis for the design of physical dummies adapted to multiple loading conditions.Firstly,a finite element foot-ankle-leg model was extracted from the Human Active Lower Limb(HALL)model established by this research group,ankle ligaments were modeled based on MRI image and foot anatomy,and the accurate material model and parameters were defined.The foot-ankle-leg model was fully validated in allowable rotation,like dorsiflexion,inversion/eversion,and external rotation.Then,its sensitivity to loading rates and initial postures was further verified through experimental data concerning both biomechanical stiffness and injury locations.The result showed that the model has good biological fidelity.Secondly,the positioning module based on the kriging algorithm was used to complete the transformation of different foot and ankle posture models.To explore the tolerance and biomechanical dynamic response of lower limbs,we established a simulation matrix to investigate the influences of different under-foot impact velocities and initial posture.The result showed that from-15° to 30°,the maximum tolerance of the tibia is in the neutral posture,and the minimum is in dorsiflexion 30°,and more than 1.5 times tolerance gap was achieved between neutral posture and dorsiflexion30°.With impact velocity increasing,the fracture force of the tibia also increases.From2 m/s to 14 m/s,the peak tibia force increased at least 1.9 times in all postures.Thus,we consider that it is necessary to include initial posture and loading rate factors in the definition of the foot-ankle-leg injury tolerance for under-foot impact loading.Finally,the dynamic responses of the lower limb under different foot impact velocities were investigated through three common knee angles,and the HALL model was coupled with the upper body of the Hybrid Ⅲ dummy model.In three typical postures,the biomechanical response characteristics of the mixture model and the Hybrid Ⅲ dummy model were compared under undamaged under-foot impact loading.A preliminary improved lower limb scheme is proposed to improve the biofidelity of the dummy for under-foot impact loadings.In a word,this study fully validated the foot-ankle-leg model and explored the injury pattern of the foot-ankle region under different impact velocities and initial postures.The improved designing scheme of the dummy lower limb was put forward by comparing the biomechanical dynamic responses of the HALL model and the dummy lower limb model to establish the lower limb which is suitable for various typical under-foot impact loading environments.It also provided a theoretical foundation for assessing the injury of the human lower limb,protection strategy,and device improvement for all kinds of under-foot impact loadings. |
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