Repeatability testing of a new Hybrid III 6-year-old ATD lower extremity

<b>Objective</b>: Vehicle safety is improving, thus decreasing the number of life-threatening injuries and increasing the need for research in other areas of the body. The current child anthropomorphic test device (ATD) does not have the capabilities or instrumentation to measure many of the potential interactions between the lower extremity and the vehicle interior. A prototype Hybrid III 6-year-old ATD lower extremity (ATD-LE) was developed and contains a tibia load cell and a more biofidelic ankle. The repeatability of the device has not yet been assessed; thus, the objective was to evaluate the repeatability of the ATD-LE. Additionally, a dynamic assessment was conducted to quantify injury threshold values. <b>Methods</b>: A pneumatic ram impactor was used at 2 velocities to evaluate repeatability. The ATD-LE was fixed to a table and impacted on the plantar aspect of the forefoot. Three repeated trials at 1.3 and 2.3 m/s without shoes and 2.3 m/s with shoes were conducted. The consistency of tibia force (N), bending moment (Nm), ankle range of motion (ROM, °), and stiffness (Nm/°) were quantified. A dynamic assessment using knee bolster airbag (KBA) tests was also conducted. The ATD-LE was positioned to mimic 3 worst-case scenarios: toes touching the mid-dashboard, touching the lower dashboard, and flat on the floor prior to airbag deployment. The impact responses in the femur and tibia were directly collected and compared with published injury threshold values. <b>Results</b>: Ram impact testing indicated primarily excellent repeatability for the variables tested. For all 3 conditions the coefficients of variance (CV) were as follows: tibia force, 1.9–2.7%; tibia moment, 1.0–2.2%; ROM, 1.3–1.4%; ankle stiffness, 4.8–15.6%. The shoe-on condition resulted in a 25% reduction in tibia force and a 56% reduction in tibia bending moment. The KBA tests indicate that the highest injury risk may be when the toes touch the lower dashboard, due to the high bending moments recorded in the tibia at 76.2 Nm, which was above the injury threshold. <b>Conclusions</b>: The above work has demonstrated that the repeatability of the ATD-LE was excellent for tibia force, bending moment, and ankle ROM. The ATD-LE has the ability to provide new information to engineers and researchers due to its ability to directly evaluate the crash response of the ankle and leg. New information on injury mechanism and injury tolerance may lead to injury reduction and thus help advance the safety of children.<b>研究目标</b>：车辆安全性能持续提升，由此降低了危及生命的损伤发生率，同时推动了人体其他部位相关碰撞安全研究的需求增长。当前的儿童拟人测试装置（Anthropomorphic Test Device, ATD）无法有效测量下肢与车辆内饰间的多种潜在交互作用。为此，研究人员开发了一款Hybrid III型6岁儿童拟人测试装置下肢原型（ATD-LE），该原型搭载了胫骨测力传感器与更具生物逼真性的踝关节。该装置的重复性尚未得到评估，因此本研究的首要目标为评估ATD-LE的重复性；此外，本研究还开展了动态评估以量化损伤阈值。 <b>研究方法</b>：为评估重复性，本研究采用气动冲锤冲击装置，设置两种冲击速度开展试验。将ATD-LE固定于试验台，对其前足跖侧实施冲击。分别开展无鞋状态下1.3 m/s、2.3 m/s速度组，以及穿鞋状态下2.3 m/s速度组的三次重复冲击试验。量化分析胫骨力（单位：牛，N）、弯矩（单位：牛·米，Nm）、踝关节活动范围（Range of Motion, ROM，单位：度，°）以及刚度（单位：牛·米/度，Nm/°）的一致性。此外，本研究还采用膝部缓冲气囊（Knee Bolster Airbag, KBA）试验开展动态评估。将ATD-LE置于三种最坏工况场景：气囊展开前，儿童足尖触碰仪表台中部、触碰仪表台下部，以及足部平贴于地板。直接采集股骨与胫骨的冲击响应数据，并与已发表的损伤阈值进行对比。 <b>研究结果</b>：气动冲锤冲击试验结果显示，所测试的各项变量均具备优异的重复性。三种工况下的变异系数（Coefficient of Variance, CV）分别为：胫骨力1.9%~2.7%、胫骨弯矩1.0%~2.2%、踝关节活动范围1.3%~1.4%、踝关节刚度4.8%~15.6%。穿鞋状态下，胫骨力降低25%，胫骨弯矩降低56%。膝部缓冲气囊试验结果表明，当足尖触碰仪表台下部时，损伤风险最高：此时测得的胫骨弯矩达76.2 Nm，超出损伤阈值。 <b>研究结论</b>：本研究结果证实，ATD-LE在胫骨力、胫骨弯矩及踝关节活动范围方面均具备优异的重复性。得益于可直接评估踝关节与下肢的碰撞响应性能，ATD-LE能够为工程师与研究人员提供全新的研究数据。针对损伤机制与损伤耐受度的全新研究数据，有望实现损伤发生率的降低，进而助力儿童车辆安全性能的提升。