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1.
A novel dynamic compressive experimental technique has been developed based on a split Hopkinson pressure bar. This new method
dynamically loads the ceramic specimen by two consecutive stress pulses. The first pulse determines the dynamic response of
the intact ceramic materiaal and then crushes the specimen, and the second pulse determines the dynamic compressive constitutive
behavior of the ceramic rubble. Precise pulse shaping ensures that the specimen deforms at nearly constant strain rates under
dynamic stress equilibrium during the loading by both stress pulses. Pulse shaping also controls the amplitudes of loading
pulses, the values of strain rates, the maximum strains in the rubble specimens, and the proper separation time between the
two loading pulses. The feasibility of the new technique is demonstrated by the experimental results obtained on an AD995
alumina. 相似文献
2.
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
3.
不同应变率下泡沫铝的形变和力学性能 总被引:3,自引:0,他引:3
对低密度泡沫铝在不同变形率下的形变和力学性能进行了系统的试验研究。结果表明:(1)沿剪切方向骨架首先塌陷,即变形的局部化是低应变率下块体泡沫铝的主要变形特征;(2)在不同应变率下泡沫铝表现出体积应变基本上随工程应变呈线性变化,在低应变率下泊松比随轴向应变呈幂次关系增加,但在高应变率下泊松比随塑性应变增加,从一峰值降低并趋于稳定;(3)低应变率下泡沫铝材料塑性变形均匀,而高应变率下剪切变形较大;(4)泡沫铝材料的强度对应变率不很明显,但随塑性应变增加,它的率敏感性增加。 相似文献
4.
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
5.
6.
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
7.
Dynamic compressive behavior of thick composite materials 总被引:3,自引:0,他引:3
The effect of strain rate on the compressive behavior of thick carbon/epoxy composite materials was investigated. Falling weight impact and split Hopkinson pressure bar systems were developed for dynamic characterization of composite materials in compression at strain rates up to 2000 s–1. Strain rates below 10 s–1 were generated using a servohydraulic testing machine. Strain rates between 10 s–1 and 500 s–1 were generated using the drop tower apparatus. Strain rates above 500 s–1 were generated using the split Hopkinson pressure bar. Unidirectional carbon/epoxy laminates (IM6G/3501-6) loaded in the longitudinal and transverse directions, and
cross-ply laminates were characterized. The 90-deg properties, which are governed by the matrix, show an increase in modulus and strength over the static values but no significant change in ultimate strain. The 0-deg and cross-ply laminates show higher strength and ultimte strain values as the strain rate increases, whereas the modulus increnases only slightly over the static value. The increase in strength and ultimate strain observed may be related to the shear behavior of the composite and the change in failure modes. In all cases, the dynamic stress-strain curves stiffen as the strain rate increases. The stiffening is lowest in the longitudinal direction and highest in the transverse direction. 相似文献
8.
分离式霍普金森杆(Split Hopkinson Bar)是测试材料在高应变率加载下力学行为的一种有效的实验手段.本文基于霍普金森杆测试原理,设计和研制了气枪式变截面间接杆杆型高应变率拉伸实验装置.该装置具有完备的、高精度的水平和轴向基准,采用等高的固定支撑,保证了杆-杆型实验系统具有良好的共轴度;入射杆与撞击套筒之间设有导向管,避免了撞击套筒直接与入射杆接触而产生的相互干扰;在导向管内设有支撑圈,以减小入射杆与导向管直接接触而产生的摩擦,并消除入射杆的径向跳动;采用前置金属短杆来获得光滑、平稳且幅值和宽度可调的拉伸入射加载脉冲.对LY12CZ铝合金在两种应变率下初步的验证性实验表明,该高应变率拉伸实验装置的设计是合理的,实验获得的应力—应变结果是可靠、有效的. 相似文献
9.
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
10.
通孔泡沫铝的动态压缩行为 总被引:4,自引:0,他引:4
在SHPB装置上对渗流法制备的通孔泡沫铝进行了动态压缩实验,研究了相对密度为0.341~0.419的通孔泡沫铝在10-3~2000 s-1应变率范围内的压缩响应特征和应变率相关性,并用扫描电镜(scanning electron microscope,SEM)分析了泡沫铝的压缩变形特征。实验结果表明,通孔泡沫铝有明显应变率效应,随应变率上升,泡沫铝流动应力提高。SEM观察结果揭示,在动态压缩下,通孔泡沫铝宏观上均匀变形,微观变形机制以泡孔横向伸展坍塌为主。 相似文献
11.
The torsional split Hopkinson bar is used for testing materials at strain rates above 104s−1. This strain rate, which is an order of magnitude higher than is typical with this technique, is obtained by using very short
specimens. Strain rates of 6.4×104s−1 have been achieved with specimens having a gage length of 0.1524 mm. Results from tests on 1100 aluminum show an increase
in rate sensitivity as the strain rate increases. 相似文献
12.
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
13.
A dynamic experimental technique that is three orders of magnitude as sensitive in stress measurement as a conventional split
Hopkinson pressure bar (SHPB) has been developed. Experimental results show that this new method is effective and reliable
for determining the dynamic compressive stress-strain responses of materials with low mechanical impedance and low compressive
strengths, such as elastomeric materials and foams at high strain rates. The technique is based on a conventional SHPB. Instead
of a surface strain gage mounted on the transmission bar, a piezoelectric force transducer was embedded in the middle of the
transmission bar of a high-strength aluminum alloy to directly measure the weakly transmitted force profile from a soft specimen.
In addition, a pulse-shape technique was used for increasing the rise time of the incident pulse to ensure stress equilibrium
and homogeneous deformation in the low-impedance and low-strength specimen. 相似文献
14.
应变率历史对记忆合金在高应变率拉伸下力学行为影响的实验研究 总被引:3,自引:0,他引:3
利用分离式拉伸霍布金森杆(SHSB)装置考察了高应变率拉伸作用下形状记忆合金的力学行为,并研究了高应变率历史对高应变率拉伸作用下力学行为的影响.研究表明,记忆合金是一种对应变率非常敏感的材料,与准静态载荷作用下应力应变关系相比,高应变率使屈服应力提高,并随着所经历的应变率水平的升高,同一高应变率下屈服强度明显增加. 相似文献
15.
首先对PVDF(polyvinylidene fluoride)压电薄膜在不同温度不同压力作用下的响应进行了系统的试验研究。然后在Hopkinson压杆系统的透射杆之间夹上PVDF压电薄膜,对其动态响应进行了检验。最后应用这个镶嵌PVDF压电薄膜的Hopkinson压杆系统,测试了泡沫铜材料在不同应变率下的应力应变关系。结果表明:(1)PVDF压电薄膜的压电常数D33是随温度和压力而变,实际应用时应对其进行标定;(2)PVDF压电薄膜可有效的用于Hopkinson压杆系统来测试低强度泡沫材料或低阻抗材料的动态响应;(3)当应变率小于0.1/s时,泡沫铜的塑性流动应力对应变率不敏感,在约400/s到5000/s应变率范围,应变小于40%下泡沫铜对应变率也不敏感。但当应变大于约20%,应变率高于400/s时,与低应变率下的值比较,塑性流动应力的应变率敏感性增加。 相似文献
16.
The split Hopkinson pressure bar (SHPB) method is used to investigate the dynamic behavior of the artificial frozen soil under the nearly uniaxial strain and uniaxial stress conditions. The tests are conducted at the temperatures of −3?C, −8?C, −13?C, −17?C, −23?C, and −28?C and with the strain rates from 900 s−1 to 1 500 s−1. The nearly uniaxial stress-strain curves exhibit an elastic-plastic behavior, whereas the uniaxial stress-strain curves show a brittle behavior. The compressive strength of the frozen soil exhibits the positive strain rate and negative temperature sensitivity, and the final strain of the frozen soil shows the positive strain rate sensitivity. The strength of the frozen soil under the nearly uniaxial strain is greater than that under the uniaxial stress. After the negative confinement tests, the specimens are compressed, and the visible cracks are not observed. However, the specimens are catastrophically damaged after the uniaxial SHPB tests. A phenomenological model with the thermal sensitivity is established to describe the dynamic behavior of the confined frozen soil. 相似文献
17.
18.
Soft polymer roll covers, which are used in certain positions of paper manufacturing machines, have a vital role in the dynamics
of two mating rotating rolls (i.e., nip dynamics). The polymer covers are often used in moist conditions where the loading
rates are rather high and temperatures may vary from 45 to 60°C. In this paper, we study the dynamic mechanical behavior of
two soft polyurethane composite roll covers under different conditions of temperature, moisture, and loading rate. For the
tests in compression, both servohydraulic materials testing machines and the split Hopkinson pressure bar technique were used
in the strain rate range of 0.001–1500 s−1. The specimens, which were to be tested under moist conditions, were immersed in paper machine water (pH 4.5) until saturated
moisture content was reached. The materials showed remarkable softening as well as decrease in the strain rate sensitivity
in moist conditions. 相似文献
19.
在测试材料动态力学性能时,直接撞击式霍布金森压杆(direct impact Hopkinson pressure bar,DIHPB)实验系统相对于分离式霍布金森压杆(split Hopkinson pressure bar,SHPB),往往能获得更高的应变率。本文中采用一种新型双剪切试样,在DIHPB系统下对603钢进行了动态剪切测试。获得了603钢在应变率1 500~33 000 s−1的剪应力-剪应变曲线,并与SHPB系统下的测试结果进行了对比。结果表明,由两种测试方法获得的流动应力具有较好的一致性,但曲线的上升沿存在明显区别。采用数值模拟对DIHPB方法的准确性进行了验证,并对该实验方法的适用条件进行了分析。采用DIHPB方法,可以观察到603钢的流动应力存在明显的应变率效应,但在较高的加载速度下材料的失效应力随着加载速度的增加而呈降低趋势。
相似文献