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1.
Polymeric split Hopkinson pressure bars are often used to test low-impedance materials at elevated strain rates. However,
they tend to be viscoelastic, and a viscoelastic wave propagation model is required to analyze the data. This considerably
complicates the analysis over the more common linear elastic split Hopkinson bar. In this research, a polymeric split Hopkinson
bar is instrumented with electromagnetic velocity gages. The gages are placed at the interfaces between the bars and the specimen.
By using this arrangement, viscoelastic effects in the bars are negligible and the need for a viscoelastic correction is eliminated.
The method is applied by testing low-density foams. 相似文献
2.
利用传统分离式霍普金森压杆(split Hopkinson pressure bar, SHPB)实验技术来实现试件在较低应变率下的大变形时,需要使用超长的压杆系统,杆件的加工和实验空间限制了该技术的推广应用。鉴于此,提出一种直撞式霍普金森压杆二次加载实验技术,利用透射杆中的应力波在其末端的准刚性壁反射实现对试件的二次加载,并分析了准刚性质量块尺寸对二次加载的影响规律;采用二点波分离方法对叠加的应力波进行了有效分离和计算,在总长4 m的压杆系统中实现了1.2 ms的长历时加载,并可以准确获得试件的加载应变率曲线和应力应变关系。建立了直撞式霍普金森压杆二次加载有限元模型,数值仿真结果表明,该实验技术能有效地实现试件的二次加载,与超长SHPB系统获得的仿真结果相比较,两者的试件应力应变关系完全一致。利用该技术对1100铝合金材料进行动态压缩实验,实现了其在102 s?1量级应变率下的大变形动态力学性能测试。 相似文献
3.
Dynamic characterization of compliant materials using an all-polymeric split Hopkinson bar 总被引:1,自引:0,他引:1
The split Hopkinson bar is a reliable experimental technique for measuring high strain rate properties of high-strength materials. Attempts to apply the split Hopkinson bar in measurement on more compliant materials, such as plastics, rubbers and foams, suffer from limitations on the maximum achievable strain and from high noise-to-signal ratios. The present work introduces and all-polymeric split Hopkinson bar (APSHB) experiment, which overcomes these limitations. The proposed method uses polymeric pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials, thus providing both a low noise-to-signal ratio data and a longer input pulse for higher maximum strain. The APSHB requires very careful data reduction procedures because of the viscoelastic behavior of the incident and transmitter pressure bars. High-quality stress-strain data for a variety of compliant materials, such as polycarbonate, polyurethane foam and styrofoam, are presented. 相似文献
4.
为提高分离式Hopkinson压杆装置的测试效率与精度,通过对电磁驱动技术的分析,设计并进行了电磁线圈驱动导体杆的原理性实验。以微型分离式Hopkinson压杆装置为基础,将电磁线圈驱动原理用于撞击杆的驱动。通过单级线圈驱动不同长度撞击杆,获得储能电量与不同长度撞击杆的速度为线性关系。结合对镁合金材料的动态应力应变关系测试结果,证明此系统速度容易控制、重复性好、可靠性高和实用性强、电磁干扰并不影响信号采集。借助此原理,通过提高储能电量或采用多级同轴线圈驱动方法,可以实现各种规格的Hopkinson压杆装置中撞击杆的有效驱动,使Hopkinson杆测试装置简化。 相似文献
5.
本文中提出单轴双向加载分离式霍普金森压杆(bidirectional-load split Hopkinson compression bar,BSHCB),即在传统的分离式霍普金森压杆(split Hopkinson pressure bar,SHPB)的基础上增加另一个对称的入射波,两边的入射波同时且对称地对试样进行动态加载。根据一维应力波传播理论,推导出单轴双向加载分离式霍普金森杆的数据处理公式。通过数值模拟分析发现,所推导的数据处理公式可以用于计算单轴双向加载实验中试样的工程应力、工程应变和工程应变率。此外,单轴双向对称加载不仅可缩短试样内部应力均匀化的过程,而且可以提高试样应变率。 相似文献
6.
We present pulse shaping techniques to obtain compressive stress-strain data for elastic-plastic materials with a split Hopkinson
pressure bar. The conventional split Hopkinson pressure bar apparatus is modified by placing a combination of copper and steel
pulse shapers on the impact surface of the incident bar. After impact by the striker bar, the copper-steel pulse shaper deforms
plastically and spreads the pulse in the incident bar so that the sample is nearly in dynamic stress equilibrium and has a
nearly constant strain rate in the plastic response region. We present analytical models and data that show a broad range
of incident strain pulses can be obtained by varying the pulse shaper geometry and striking velocity. For an application,
we present compressive stress-strain data for 4340 Rc 43 steel. 相似文献
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分离式Hopkinson压杆实验技术研究进展 总被引:6,自引:0,他引:6
分离式Hopkinson压杆(split Hopkinson pressure bar,
SHPB)技术是一种广泛应用于研究材料加载应变率在($10^{2}\sim
10^{4}{\rm s}^{- 1}$)范围内力学响应的实验方法.
在详细介绍Hopkinson, Davies和Kolsky的3篇经典论文的基础上,
从基本理论研究、加载波形控制、复合加载方式以及测试系统改进4个方面详细论述SHPB实验技术的研究进展.
通过分析SHPB实验技术在实际应用中存在的问题,
提出SHPB标准化、拓宽应用范围以及广义SHPB技术是SHPB实验技术研究值得深入探索的方向. 相似文献
9.
Pulse shaping techniques for testing brittle materials with a split hopkinson pressure bar 总被引:38,自引:0,他引:38
We present pulse shaping techniques to obtain compressive stress-strain data for brittle materials with the split Hopkinson
pressure bar apparatus. The conventional split Hopkinson pressure bar apparatus is modified by shaping the incident pulse
such that the samples are in dynamic stress equilibrium and have nearly constant strain rate over most of the test duration.
A thin disk of annealed or hard C11000 copper is placed on the impact surface of the incident bar in order to shape the incident
pulse. After impact by the striker bar, the copper disk deforms plastically and spreads the pulse in the incident bar. We
present an analytical model and data that show a wide variety of incident strain pulses can be produced by varying the geometry
of the copper disks and the length and striking velocity of the striker bar. Model predictions are in good agreement with
measurements. In addition, we present data for a machineable glass ceramic material, Macor, that shows pulse shaping is required
to obtain dynamic stress equilibrium and a nearly constant strain rate over most of the test duration. 相似文献
10.
A split Hopkinson pressure bar technique to determine compressive stress-strain data for rock materials 总被引:14,自引:0,他引:14
This paper presents a split Hopkinson pressure bar technique to obtain compressive stress-strain data for rock materials.
This technique modifies the conventional split Hopkinson bar apparatus by placing a thin copper disk on the impact surface
of the incident bar. When the striker bar impacts the copper disk, a nondispersive ramp pulse propagates in the incident bar
and produces a nearly constant strain rate in a rock sample. Data from experiments with limestone show that the samples are
in dynamic stress equilibrium and have constant strain rates over most of the test durations. In addition, the ramp pulse
durations can be controlled such that samples are unloaded just prior to failure. Thus, intact samples that experience strains
beyond the elastic region and postpeak stresses can be retrieved for microstructural evaluations. The paper also presents
analytical models that predict the time durations for sample equilibrium and constant strain rate. Model predictions are in
good agreement with measurements. 相似文献
11.
基于三维Hopkinson杆的混凝土动态力学性能研究 总被引:1,自引:0,他引:1
混凝土、岩石类材料在复杂应力状态下的动态力学性能研究一直备受关注,但鉴于动态实验的复杂性,对真三轴应力状态下材料的动态加载一直未曾实现。本文中研制了一套真三轴静载作用下混凝土、岩石类材料的“三维Hopkinson杆”动态力学实验系统,为冲击载荷作用下材料动态各向异性特性的研究提供了一种有效的实验测试技术。该系统采用液压伺服控制对立方体试件施加三向独立的0~100 MPa真三轴静载,再利用分离式Hopkinson压杆对试件施加冲击动载,具体研究了C30混凝土材料在不同真三轴静载条件下的动态压缩性能,得到了不同条件下X、Y、Z方向上的动态应力应变关系。 相似文献
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运用Holmquist-Johnson-Cook (HJC) 本构模型对混凝土的SHPB实验进行了数值模拟。解决了罚函数算法中罚因子合理数值的选取问题。利用模拟结果按SHPB两波法重构了试样的应力应变曲线。分析了混凝土材料的SHPB实验得到应力应变曲线的有效段范围和各段的力学规律。通过比较实际混凝土材料SHPB实验和数值模拟得到的应力应变曲线,发现两者体现的力学行为很相似,即HJC模型是描述该类材料的一种合理本构模型。模拟了试样不同平行度公差下的SHPB实验,发现在一定应变率范围内其影响程度远大于试样应力(应变)不均匀性。 相似文献
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17.
Upper limit of constant strain rates in a split Hopkinson pressure bar experiment with elastic specimens 总被引:1,自引:0,他引:1
The upper limit of the achievable constant strain rates in linearly elastic specimens loaded by a split Hopkinson pressure
bar is estimated based on the specimen properties and a linear ramp loading. The criterion for a plateau of constant strain
rate is derived and discussed. Dynamic experimental results on an S-2 glass/SC15 composite and polymethyl-methacrylate subjected
to various ramp loadings verify the modeling results. 相似文献
18.
动态加载装置和动态测试技术 总被引:4,自引:0,他引:4
本文介绍了力学试验中各种类型冲击加载装置及有关的动态测试技术,讨论了分段式Hopkinson压杆装置的加载特性、主要优点、用途以及在该装置上采用的一些测量新技术。文章中提出的应力波调节器,结构简单,重复性好,是动态光测技术中一种崭新的冲击加载装置。 相似文献
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A split Hopkinson bar technique for low-impedance materials 总被引:9,自引:0,他引:9
An experimental technique that modifies the conventional split Hopkinson pressure bar has been developed for measuring the compressive stress-strain responses of materials with low mechanical impedance and low compressive strengths such as elastomers at high strain rates. A high-strength aluminum alloy was used for the bar materials instead of steel, and the transmission bar was hollow. The lower Young's modulus of the aluminum alloy and the smaller cross-sectional area of the hollow bar increased the amplitude of the transmitted strain signal by an order of magnitude as compared to a conventional steel bar. In addition, a pulse shaper lengthened the rise time of the incident pulse to ensure stress equilibrium and homogeneous deformation in the low-impedance specimen. Experimental results show that the high strain rate, compressive stress-strain behavior of an elastomeric material can be determined accurately and reliably using this technique. 相似文献