应力脉冲在SHPB实验中弥散效应的数值模拟与频谱分析

在评判不同材料的整形器对加载波形的改进效果的应用背景下,对比研究了不同形态的应力脉冲在霍普金森压杆(split Hopkinson pressure bar,SHPB)中的弥散效应。利用有限元软件LS-DYNA建立了杆件的三维有限元模型,在杆端分别施加矩形、三角形和半正弦形的应力脉冲,分析了波形振荡、前沿升时和应力峰值随传播距离的变化规律,并运用频谱分析的方法进行了理论解释。结果表明:三角应力脉冲和半正弦应力脉冲在各个方面都比传统的矩形应力脉冲表现出了更小的弥散效应;半正弦应力脉冲在传播过程中比三角应力脉冲更能控制其形态,能有效地减少弥散效应,提高Φ100mm SHPB实验精度,是岩石类非均质材料的理想加载波形;频谱分析的方法能从理论方面有效地解释应力脉冲信号在SHPB实验中的弥散现象。由此可见,波形整形设计的理想目标为具有较宽历时的半正弦应力脉冲。

Numerical Simulation and Spectrum Analysis of Dispersion Effect of Stress Pulse in SHPB Experiment

In the background of evaluating the improving effect of pulse shaper on loading waveform, stress pulse dispersion effect of different waveforms was compared and studied based on a split Hopkinson pressure bar (SHPB). Three-dimensional finite element model of the bar was established with the help of software LS-DYNA, and rectangle, triangle and half-sine stress pulse were applied on end of bar. The wave oscillation, peak stress and wave rising time vs. propagation distance were analyzed, a theoretical explanation about this relation was presented by means of spectrum analysis. Results indicate that the triangle stress pulse and half-sine stress pulse show less dispersion effect than rectangle stress pulse in every respect; half-sine stress pulse keeps its characteristics better than triangle stress pulse. So half-sine stress pulse may effectively reduce dispersion effect and improve accuracy of 100-mm-diameter SHPB experiment, and is an appropriate loading waveform for brittle materials such as rocks. Spectrum analysis can effectively explain the stress pulse dispersion phenomenon in SHPB experiment from aspect of theory. This shows that the ideal goal of waveform shaping is half-sine stress pulse with a wider period of time.