猪股骨常应变率动态压缩试验方法研究

Dynamic compressive testing method of pig femoral cortical bone

准确的骨骼材料响应对于模拟交通事故、战争和跌落中的人体损伤机制作用重大,但上述工况所对应的皮质骨动态力学响应还没有在常应变率条件下被规范测量。为在动态压缩试验中实现和维持不同的恒定应变率,建立针对皮质骨的重复性良好的霍普金森杆动态材料测试方法,并测试大应变率范围内的骨骼材料力学参数。首先测试纯铝整形器尺寸和子弹撞击入射杆速度对入射脉冲形状的改变效果,并在此基础上不断改变入射脉冲形状直至满足常应变率条件,随后对32个加工规则的猪股骨中轴皮质骨试样按照应变率范围进行分组测量。当入射波平台部分斜率与透射波上升沿斜率相等时,试样以常应变率变形,此时常应变率产生的变形超过总应变量的70%。猪股骨皮质骨在200~1500 s 1应变率间极限应力和极限应变增大(分别为10.2%与25.0%),弹性模量减小(7%)。结果表明,相对于杆材料更软的塑性金属作为整形器能使骨骼在需要的应变率范围内保持应变率恒定,且重复性良好,适宜进一步用于人骨测试。

Accurate skeletal material response plays an important role for simulating the mechanism of human injury among traffic accidents,wars,and falls,but the dynamic mechanical response of cortical bone corresponding among such load-cases has not been measured under constant strain rate conditions.The present study,thus,aims to achieve and sustain different constant strain rates in dynamic compression,establish a repeatable testing method and reveal the material properties of cortical bone at a wide strain rate range.Effect of the size of aluminum pulse shaper and velocity of the striker on the incent pulse was firstly tested,based on which the incent pulse was adjusted to satisfy the constant strain rate condition.Then,32 regular machined cortical bone harvested at mid-shaft of pig femurs were divided into 3 groups according to the target strain rate ranges and tested at constant strain rates.As results,constant strain rates condition were only achieved when the slope of incent pulse equals to that of transmit pulse and caused more than 70%of specimen strain.By ncreasing the strain rate from 200 s−1 to 1500 s−1,the average ultimate strain was increased by 25.0%,ultimate stress was increased by 10.2%,while Young's modulus was decreased by 7.0%.The testing method established by present work based on plastic deformation of relatively softer metal can be easily repeated and suitable for the following test of human cortical bone.