基于PVDF薄膜传感器的猪肝动态压缩力学性能测试

瞬态冲击载荷作用下肝脏的力学响应是损伤生物力学的重要研究内容。本文提出了一种可用于软组织动态压缩力学特性测试的改进SHPB(分离式霍普金森压杆,Split Hopkinson Pressure Bar)方法。该方法采用PVDF(聚偏氟乙烯,Polyvinylidene Fluor)压电薄膜传感器测量实验过程中试件两端面的受力,以此来计算试件的应力,从而无需测量透射杆上的微弱透射信号。猪肝试样前后端面的PVDF压电信号对比表明,加载过程中试样达到了动态应力平衡状态。试样动态压缩中的惯性效应主要在加载的初始阶段对透射应力信号造成较大影响,在大变形阶段惯性效应引起的轴向应力较小。利用此方法对猪肝组织进行三种高应变率(1800s^-1,2500s^-1,3500s^-1)的动态压缩实验,并采用基于真实应变的惯性效应公式对实验数据进行修正计算。结果表明:猪肝组织在准静态与高应变率时的应力应变曲线都呈现出凹向上的非线性特征,即曲线初始阶段应力增长较缓慢,当应变达到15%后应力值则迅速增大;猪肝组织也具有明显的应变率效应,即随着应变率的增加,应力应变曲线的整体应力值也随之增大。最后,采用黏超弹性本构模型描述了猪肝组织的动态应力应变曲线。

Dynamic compression mechanical properties of porcine liver based on PVDF piezoelectric film sensor

The mechanical response of the liver under transient impact loads is an important research content of injury biomechanics.In this work,an improved Split Hopkinson Pressure Bar(SHPB)method is presented to test the dynamic compression mechanical properties of soft tissues.Polyvinylidene fluor(PVDF)piezoelectric film sensors are used to measure the stresses on two ends of the specimen during the experiment,so as to calculate the stress of the specimen without measuring the weak transmission signals on the transmission rod.The comparison of PVDF stress signals between the front and the back of the porcine liver specimen shows that the specimen achieves dynamic stress equilibrium during loading.The inertia effect on the dynamic compression of the specimen mainly affects the transmitted stress signal at the initial stage of loading,while the axial stress caused by the inertia effect is relatively small at the stage of large deformation.Three kinds of dynamic compression experiments with high strain rates(1800s-1,2500s-1,3500s-1)are carried out in porcine liver tissue by this method,and the experimental data are fitted by the inertial effect formula based on the real strain.The results show that the stress-strain curves of the porcine liver tissue at quasi-static and high strain rate show concave nonlinear characteristics,that is,the stress increases slowly in the initial stage of the curve,and the stress value increases rapidly when the strain reaches 15%.The porcine liver tissue also has obvious strain rate effect stress,that is,the overall stress-strain value of the stress-strain curve increases while the increases of strain rate.Finally,a viscoelastic constitutive model is constructed to describe the dynamic stress-strain curve of porcine liver.