肌肉类粘弹性超软材料SHPB实验的应力应变均匀性分析

Analysis of Stress and Strain Uniformity of Muscle-Like Extra-Soft Viscoelastic Material in SHPB Experiment

试样的轴向应力和应变均匀问题是霍普金森杆实验行之有效的必要条件,而这对肌肉类粘弹性超软材料尤为重要。本文用量纲分析法,分析出了影响粘弹性材料SHPB实验应力和应变均匀性的无量纲量,结合LS-DYNA数值模拟方法,考察了各无量纲量对粘弹性材料均匀性的影响规律。结果表明,为使肌肉类材料SHPB实验更早达到均匀条件,理想的入射波是升时为tr=2sτ的梯形波;试样与杆的波阻抗比β1/21;当试样长度ls Xeff/4("有效传播距离"Xeff=Cssθ)时,可以忽略粘弹性对应力和应变均匀的影响,但由于粘弹性参数在实验前未知,该公式不能用来确定试样尺寸。采用石英等传感器实时检测试样应力均匀性十分重要,梯形波加载时,若应力进入均匀状态,则认为变形也达到均匀。

Validity of SHPB test is based on assumption of the axial stress and strain uniformity within specimen, and is especially important for muscle-like viscoelastic extra-soft material. Dimensionless parameters influencing the stress and strain uniformity of viscoelastic material subjected to SHPB test were analyzed based on dimension analysis, and the influence of dimensionless parameters on the uniformity of viscoelastic material was investigated by using LS-DYNA numerical simulation. Results show that in order to attain uniformity requirement earlier in SHPB test for muscle-like material, the ideal incident wave is a trapezoidal wave with 2τ rising time, and the desirable wave impedance ratio of specimen and bar is not greater than 1/21. If the length of bar ls〈Xeff/4 （effective propagation distance Xeff=Csθs）, the effect of viscoelasticity on the stress and strain uniformity can be neglected. However, the specimen size can＇t be determined based on lx〈Xeff/4 since the viscoelastic parameters are not known yet before test. Quartz crystal transducers are necessary to detect the dynamic stress equilibrium process of specimen. Since the strain uniformity is attained earlier than stress uniformity when the incident wave is the trapezoidal, so if transducers demonstrate that the stress uniformity is attained, then the strain is also regarded as uniform.