确定SHPB实验中延迟时间的曲线拟合法

 利用已知的试件密度，用预估的透射波与实测的透射波进行早期形状比较，确定试件弹性波速度，进而确定了SHPB试验数据处理时的延迟时间。     

基于FDM-DEM耦合的冲击损伤大理岩静态断裂力学特征研究

为探究循环冲击损伤后大理岩的静态断裂力学特征,基于有限差分（finite difference method,FDM）-离散元（discrete element method,DEM）耦合的建模技术构建了三维分离式霍普金森压杆（split Hopkinson pressure bar,SHPB）数值模型,其中杆件系统和岩石试件分别采用FLAC3D和PFC3D程序建模。利用该模型对中心直切槽半圆盘（NSCB）试样进行了恒定子弹速度下的循环冲击,随后对受损试样进行静态三点弯曲断裂实验。通过编写Fish程序,提取试样断裂面数据,对断裂面进行重构并定量计算表面粗糙度。通过与相关室内实验结果的对比分析,验证了本文数值分析的合理性与可靠性。模拟结果表明,随着循环冲击次数的增加,试样内部微裂纹、破碎颗粒均增加。连接力场分布混乱,部分力链发生断裂。力链的变化是试样力学性能劣化的根本原因。在静态三点弯曲断裂实验中,冲击5次后试样的静态断裂韧度较天然试样产生一定程度的降低。试样在静载过程中产生的微裂纹和碎块的数量随循环冲击次数的增加而增加,断裂面粗糙度随循环冲击次数的增加而增加。     

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...     

中心直裂纹平台巴西圆盘复合型动态断裂实验研究

制作了中心直裂纹平台巴西圆盘（cracked straight through flattened Brazilian disc-CSTFBD）试样,利用分离式霍普金森压杆（split Hopkinson pressure bar-SHPB）加载,进行了岩石纯Ⅰ型和复合型（Ⅰ＋Ⅱ型）动态断裂实验。由于加载角（载荷方向与裂纹线的夹角）在制作试样时已经通过裂纹线与试样平台的位置关系确定,因此在实验中可以方便而准确地实施加栽。比较了纯Ⅰ型加载和复合型加载下压杆上记录的入射波、反射波和透射波的波形。采用实验与数值相结合的方法,将实验得到的动态载荷输入有限元程序,得到了纯Ⅰ型试样的动态断裂韧度和复合型试样的两种动态应力强度因子的时间历程。计算了加载角为15°的试样应力强度因子的复合比（KI（t）／KⅡ（t））,此计算值与文献结果吻合较好,验证了实验方法的有效性。     

夹层对陶瓷/装甲钢复合结构应力波传播及抗弹性能影响

选取陶瓷/装甲钢复合结构为研究对象,开展霍普金森压杆试验(SHPB),研究夹层材料对复合结构应力波传播与能量耗散的影响;采用12.7 mm穿甲燃烧弹对不同夹层复合结构进行靶试验证,开展夹层材料对复合结构抗弹性能的研究. 结果表明:在陶瓷/装甲钢复合结构中引入合适的夹层材料作为过渡层,对应力波衰减起到一定改善作用;能显著提高复合结构的抗弹性能.     

Influence of Molecular Conformation on the Constitutive Response of Polyethylene: A Comparison of HDPE, UHMWPE, and PEX

The current work presents the characterization and comparison of the mechanical response of three different industrial forms of polyethylene. Specifically, high-density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE), and cross-linked polyethylene (PEX) were tested in compression as a function of temperature (−75 to 100°C) and strain-rate (10⁻⁴ to 2,600 s⁻¹). The responses of UHMWPE and PEX are very similar, whereas HDPE exhibits some differences. The HDPE samples display a significantly higher yield stress followed by a flat flow behavior. Conversely UHMWPE and PEX both exhibit significant strain hardening after yield. The temperature and strain-rate dependence are captured by simple linear and logarithmic fits over the full range of conditions investigated. The yield behavior is presented in terms of an empirical mapping function that is extended to analytically solve for the mapping constant. The power-law dependence on strain-rate observed in some polymers is explained using this mapping function.     

α-钛合金TA6的动态力学性能和剪切现象分析

诸多文献已经报道了β和(α β)钛合金冲击和爆炸加载下的绝热剪切现象,本文利用分离式的Hopkinson压杆和反射式Hopkinson拉杆对α-钛合金TA6的动态力学性能进行研究,得到不同应变率下材料的应力-应变曲线,发现钛合金TA6和其他钛合金一样也是一种应变率敏感材料。冲击拉伸加载时破坏形状45度剪切断口,然而其在冲击压缩应力作用下体现为典型的韧性,并未出现其它类型钛合金通常会出现的绝热剪切破坏。进一步分析表明:α-钛合金TA6不同于β和(α β)的钛合金,α-钛合金TA6相对于β和(α β)的钛合金是一种绝热剪切不敏感的材料。同时也利用应力状态的柔韧系数的概念对拉伸时45度的剪切断口解释。     

A rigorous assessment of the benefits of miniaturization in the Kolsky bar system

A rigorous experimental and numerical assessment is made of the benefits and limits of miniaturization in the Kolsky bar system. The primary issues that arise in very high strain rate testing (stress equilibration, inertial effects, wave dispersion, friction, and controllability of deformations) are addressed through experiments coupled with explicit finite element analyses. A miniaturized Kolsky bar system that includes the input bar is developed, together with the use of the laser occlusive radius detector to obtain local measurements of specimen strain during the very high rate deformations. It is demonstrated that this miniaturized Kolsky bar system can be used to provide fully validated results, including the explicit determination of equilibration, over a very wide range of strain rates (1×10³ to 5×10⁴ s⁻¹). The desired high strain rate can be achieved even at low accumulated strains, and the total strain developed can be controlled very effectively. Specific conditions are developed for determining the range of utility of the technique for a given material. The technique is applied to the characterization of 6061-T651 aluminum, and the results are compared with the results obtained using a conventional Kolsky bar.     

Dynamic and Quasi-Static Propagation of Compaction Waves in a Low-Density Epoxy Foam

We conducted dynamic and quasi-static compression experiments with low-density (ρ = 120 kg/m³) epoxy foam specimens. The specimens had a 10.0-mm-square cross-section and a length of 19.3 mm. Dynamic experiments were conducted with a modified split Hopkinson pressure bar (SHPB), and the quasi-static experiments were conducted with a hydraulic load frame device (MTS-810). In both cases, the specimens were loaded from one end at a constant velocity. Equally spaced grid lines were marked on the specimens to monitor the deformation history. Digital images taken at equally spaced time intervals gave the positions of each grid line. These images showed that a constant end-face velocity V produced a compaction wave front that traveled at a constant velocity C in both dynamic and quasi-static experiments. We described these results with a shockwave analysis that used a locking solid material model.     

PVDF应力测量技术及在混凝土冲击实验中的应用

介绍了使用PVDF(polyvinylidene fluoride,聚偏二氟乙烯)应力计的应力直接测量技术。在SHPB装置上进行自制PVDF应力计动态压电系数的标定实验,分析了应力集中、横向泊松效应、摩擦效应对PVDF应力计信号及动态压电系数的影响。用PVDF应力计进行了混凝土的冲击压缩实验。利用混凝土前后端面PVDF应力计信号分析了实验过程中混凝土试样的应力均匀性。与应变计直测应变技术相结合得到了混凝土的动态应力-应变关系。