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The condition of dynamic stress equilibrium is not satisfied automatically when a split Hopkinson pressure bar (SHPB) is employed
to determine the dynamic properties of soft materials. In order to develop guidelines for the proper design of SHPB experiments
under valid testing conditions, an integrated experimental/analytical study has been conducted to examine the process of dynamic
stress equilibrium in a soft rubber specimen. Dynamic compressive experiments on a RTV 630 and an ethylene-propylene-diene
monomer rubber with a SHPB modified for soft material testing were conducted to determine the effects of specimen thickness
and loading rate on the stress equilibrating process. An analytical model was employed to analyze the equilibrating processes
observed in experiments. It is found that the incident loading rate dominates the initial non-equilibrium stress state, and
the specimen thickness mainly affects the dynamic stress equilibrium after the initial stage. 相似文献
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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
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金属材料在复杂载荷条件下的动态力学行为研究一直备受关注,但受限于实验设备,金属材料的动态包辛格效应响应一直都难以获得。为了探究金属材料的包辛格效应与应变率效应之间的关系,本文中提出一种基于电磁霍普金森杆(electromagnetic split Hopkinson bar,ESHB) 的非同步加载实验技术,为测试金属材料在高应变率加载下的包辛格效应提供了一种有效的实验方法。本文中,首先介绍了非同步加载装置的主要特点,即可以用两列由脉冲发生器产生的应力波对受载试样进行连续的一次动态拉-压循环加载,且加载过程保证了应力波的一致性。分析了应力波对试样加载过程中的波传播历程,确保了加载过程的连续性。随后介绍了动态加载过程,数据处理方法和波形分离手段,并对动态加载过程进行应力平衡性分析,论证了实验装置的可靠性。最后采用该方法测试了5%预应变下6061铝合金动态压缩-动态拉伸的包辛格效应,并与准静态下的实验结果进行对比。实验结果表明,该材料单轴压缩没有明显的应变率效应,但其包辛格效应具有应变率依赖性,高应变率下材料的包辛格应力影响因子由0.07增大至0.17,具有显著的提升,这对传统意义上铝合金材料应变率不敏感的结论提出了挑战。
相似文献6.
Dynamic fracture toughness of high strength metals under impact loading: increase or decrease 总被引:1,自引:0,他引:1
An elusive phenomenon is observed in previous investigations on dynamic fracture that the dynamic fracture toughness(DFT) of high strength metals always increases with the loading rate on the order of TPa.m 1 /2.s 1.For the purpose of verification,variation of DFT with the loading rate for two high strength steels commonly used in the aviation industry,30CrMnSiA and 40Cr,is studied in this work.Results of the experiments are compared,which were conducted on the modified split Hopkinson pressure bar(SHPB) apparatus,with striker velocities ranging from 9.2 to 24.1 m/s and a constant value of 16.3 m/s for 30CrMnSiA and 40Cr,respectively.It is observed that for 30CrMnSiA,the crack tip loading rate increases with the increase of the striker velocity,while the fracture initiation time and the DFT simultaneously decrease.However,in the tests of 40Cr,there is also an increasing tendency of DFT,similar to other reports.Through an in-depth investigation on the relationship between the dynamic stress intensity factor(DSIF) and the loading rate,it is concluded that the generally increasing tendency in previous studies could be false,which is induced from a limited striker velocity domain and the errors existing in the experimental and numerical processes.To disclose the real dependency of DFT on the loading rate,experiments need to be performed in a comparatively large striker velocity range. 相似文献
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确定材料在高温高应变率下动态性能的Hopkinson杆系统 总被引:15,自引:4,他引:11
描述了一种利用Hopkinson杆装置确定在高温(温度可高达1 173 K)、高应变率下材料动态性能的试验方法。在试样加温过程中,试样不与入射杆及透射杆接触。当试样加热到预定温度时,气压驱动同步组装系统,推动透射杆及试样,使得应力波到达入射杆与试样接触面时,入射杆、试样及透射杆紧密接触。利用以上系统,完成了连铸单晶铜及上引法连铸多晶铜从室温到1 085 K范围内的应力应变曲线。测试结果表明,不论是上引法连铸多晶铜还是连铸单晶铜,流动应力随温度的升高而下降,在温度低于585 K时,材料的应变硬化率明显大于在温度高于585 K时的应变硬化率。 相似文献
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By way of numerical simulation, a method is developed to determine the parameters of the thermomechanical Bodner-Partom model
of flow under high strain rate deformation using a split Hopkinson bar. The classical method is generalized in two directions.
To evaluate the kinematic hardening parameters, the wave reflected from the free end of the bar is used. The thermomechanical
parameters that are responsible for the stored energy of cold work are calculated from measurements of temperature changes
in the specimen
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Translated from Prikladnaya Mekhanika, Vol. 44, No. 6, pp. 81–92, June 2008. 相似文献
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A new experimental technique has been developed for the performance of high temperature, high-strain-rate experiments in the compression Kolsky bar (split-Hopkinson pressure bar or SHPB). The new technique (referred to as the High-Temperature Compression Kolsky Bar or HTCKB) uses an infra-red spot-heater to rapidly heat the specimen to the desired temperature, a!nd an electropneumatic actuation system to minimize the development of temperature gradients in the sample. The technique is cheap and relatively easy to implement and yet provides accurate, repeatable results. As an illustration of the application of the technique, we have examined the high-temperature response of the BCC metal vanadium at high-strain rates. Stress–strain curves are obtained for the material at strain rates of 4 × 103 s−1 and at temperatures ranging from 300 to 1100 K (27–800°C). Quasistatic (10−3 s−1) experiments have also been performed on vanadium over a slightly smaller range of temperatures, and the results are compared with the new high-temperature, high-strain-rate data. It is observed that the rate of thermal softening is a function of the strain rate. These results illustrate the importance of including the coupling between temperature and strain r!ate in thermoviscoplastic constitutive models. 相似文献
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几种高性能纤维束的冲击动力学性能实验研究 总被引:6,自引:0,他引:6
利用直拉式Hopkinson装置研究了碳纤维、无碱E玻璃纤维、Kevlar 4 9/96 4 /96 4c、Twaron2 0 0 0、DyneemaSk6 6等纤维的动态拉伸性能。与准静态加载条件下相比 ,纤维束的拉伸强度基本与应变速率无关(玻璃纤维除外 ) ,而纤维束的弹性模量和失效应变随应变率的升高而明显变大。从高分子物理以及两种无机纤维的内部微观结构特征对纤维的力学性能与加载速率的关系进行了初步的物理阐释。讨论了实验数据的发散原因。 相似文献
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利用加长型分离式霍普金森压杆(入射杆长6000mm、子弹长800mm)研究聚氨脂泡沫材料在较
低应变率大应变条件一维应力状态下的动态力学性能,获得了约550s的长加载脉冲,得到了该材料在应变
率520s-1、应变0.15条件下的应力应变曲线,对较低应变率条件下,应变率与动态应力平衡之间的关联进行
了讨论。 相似文献