共查询到20条相似文献,搜索用时 15 毫秒
1.
A dynamic bulge testing technique is developed to perform biaxial tests on metals at high strain rates. The main component
of the dynamic testing device is a movable bulge cell which is directly mounted on the measuring end of the input bar of a
conventional split Hopkinson pressure bar system. The input bar is used to apply and measure the bulging pressure. The experimental
system is analyzed in detail and the measurement accuracy is discussed. It is found that bars made of low impedance materials
must be used to achieve a satisfactory pressure measurement accuracy. A series of dynamic experiments is performed on aluminum
6111-T4 sheets using viscoelastic nylon bars to demonstrate the capabilities of the proposed experimental technique. The parameters
of the rate-dependent Hollomon–Cowper–Symonds J2 plasticity model of the aluminum are determined using an inverse analysis
method in conjunction with finite element simulations. 相似文献
2.
Determination of Early Flow Stress for Ductile Specimens at High Strain Rates by Using a SHPB 总被引:1,自引:0,他引:1
In a dynamic experiment to obtain the high-rate stress–strain response of a ductile specimen, it takes a finite amount of
time for the strain rate in the specimen to increase from zero to a desired level. The strain in the specimen accumulates
during this strain-rate ramping time. If the desired strain rate is high, the specimen may yield before the desired rate is
attained. In this case, the strain rates at yielding and early plastic flow are lower than the desired value, leading to inaccurate
determination of the yield strength. Through experimentation and analysis, we examined the validity and accuracy of the flow
stresses for ductile materials in a split Hopkinson pressure (SHPB) bar experiment. The upper strain-rate limit for determining
the dynamic yield strength of ductile materials with a SHPB is identified. 相似文献
3.
提出了一种新的基于Hopkinson杆实验技术的在102~103s-1高应变率下实现压剪复合加载的实验装置,并给出了相应的理论分析和数值模拟。为了获取材料在复杂应力下的本构关系,借助斜飞片冲击实验的思想,对Hopkinson杆进行改造,将入射杆的末端改进为截锥形,以便在试样中同时产生压缩和剪切应力。利用有限元分析软件LS-DYNA对试样中的应力波传播进行模拟计算,并利用改进装置进行了初步实验。计算和分析结果表明,利用所设计的装置可以实现对试样的动态压剪复合加载,获得材料在高应变率复杂应力加载下的本构响应,进而建立材料在复杂应力状态下本构行为的描述。 相似文献
4.
The strength of materials at high strain levels has been determined using the so-called Continuous-Bending-under-Tension (CBT) test. This is a modified tensile test where the specimen is subjected to repetitive bending at the same time. This test enables to create high levels of uniform strain. A wide variety of materials has been tested this way. The strength of the material after CBT testing has been measured in different ways: by secondary tensile tests, by interrupted CBT tests, and directly from the fracture in the CBT test. All methods yield similar results: the strength is largely unaffected by the cyclic pre-deformation and mainly depends on the overall increase in length. Only for multi-phase materials the strength shows a minor influence of CBT test conditions. The hardening follows the extrapolated hardening observed in a conventional tensile test, except for brass. This test method can potentially be used for measuring hardening curves at high strain levels. 相似文献
5.
The characterization of soft or low impedance materials is of increasing importance since these materials are commonly used
in impact and energy absorbing applications. The increasing role of numerical modeling in understanding impact events requires
high-rate material properties, where the mode of loading is predominantly compressive and large deformations may occur at
high rates of deformation. The primary challenge in measuring the mechanical properties of soft materials is balancing the
competing effects of material impedance, specimen size, and rate of loading. The traditional Split Hopkinson Pressure Bar
approach has been enhanced through the implementation of polymeric bars to allow for improved signal to noise ratios and a
longer pulse onset to ensure uniform specimen deformation. The Polymeric Split Hopkinson Pressure Bar approach, including
the required viscoelastic bar analysis, has been validated using independent measurement techniques including bar-end displacement
measurement and high speed video. High deformation rate characterization of 10% and 20% ballistic gelatin, commonly used as
a soft tissue simulant, has been undertaken at nominal strain rates ranging from 1,000 to 4,000/s. The mechanical properties
of both formulations of gelatin exhibited significant strain rate dependency. The results for 20% gelatin are in good agreement
with previously reported values at lower strain rates, and provide important mechanical properties required for this material. 相似文献
6.
A modified miniaturized version of the Direct Impact Compression Test (DICT) technique is described in this paper. The method
permits determination of the rate-sensitive plastic properties of materials up to strain rate ∼105 s−1. Miniaturization of the experimental setup with specimen dimensions: diameter d
S = 2.0 mm and thickness l
S = 1.0 mm, Hopkinson bar diameter 5.2 mm, with application of a novel optical arrangement in measurement of specimen strain,
makes possible compression tests at strain rates from ∼103 s−1 to ∼105 s−1. In order to estimate the rate sensitivity of a low-alloy construction steel, quasi-static, Split Hopkinson Pressure Bar
(SHPB) and DICT tests have been performed at room temperature within the rate spectrum ranging from 5*10−4 s−1 to 5*104 s−1. Adiabatic heating and friction effects are analyzed and the final true stress versus true strain curves at different strain
rates are corrected to a constant temperature and zero friction. The results have been analyzed in the form of true stress
versus the logarithm of strain rate and they show two regions of a constant rate sensitivity : relatively low up to the strain rate threshold ∼50 s−1, and relatively high above the threshold, up to strain rate ∼4.5*104 s−1. 相似文献
7.
Experimental Mechanics - Limited methods exist for the characterization of interfacial properties in fiber reinforced composites under dynamic loading conditions since conventional techniques are... 相似文献
8.
An Experimental Method to Determine the Tensile Strength of Concrete at High Rates of Strain 总被引:1,自引:0,他引:1
In the present work, dynamic tensile strength of concrete is experimentally investigated by means of spalling tests. Based on extensive numerical simulations, the paper presents several advances to improve the processing of spalling tests. The striker is designed to get a more uniform tensile stress field in the specimen. Three methods proposed in the literature to deduce the dynamic strength of the specimen are discussed as well as the use of strain gauges and a laser extensometer. The experimental method is applied to process data of several tests performed on wet micro-concrete at strain rates varying from 30 to 150/s. A significant increase of the dynamic tensile strength with strain-rate is observed and compared with data of the literature. In addition, post-mortem studies of specimens are carried to improve the analysis of damage during spalling tests. 相似文献
9.
Tensile tests with simultaneous full-field strain and temperature measurements at the nominal strain rates of 0.01, 0.1, 1, 200 and 3000 s?1 are presented. Three different testing methods with specimens of the same thin and flat gage-section geometry are utilized. The full-field deformation is measured on one side of the specimen, using the DIC technique with low and high speed visible cameras, and the full-field temperature is measured on the opposite side using an IR camera. Austenitic stainless steel is used as the test material. The results show that a similar deformation pattern evolves at all strain rates with an initial uniform deformation up to the strain of 0.25–0.35, followed by necking with localized deformation with a maximum strain of 0.7–0.95. The strain rate in the necking regions can exceed three times the nominal strain rate. The duration of the tests vary from 57 s at the lowest strain rate to 197 μs at the highest strain rate. The results show temperature rise at all strain rates. The temperature rise increases with strain rate as the test duration shortens and there is less time for the heat to dissipate. At a strain rate of 0.01 s?1 the temperature rise is small (up to 48 °C) but noticeable. At a strain rate of 0.1 the temperature rises up to 140 °C and at a strain rate of 1 s?1 up to 260 °C. The temperature increase in the tests at strain rates of 200 s?1 and 3000 s?1 is nearly the same with the maximum temperature reaching 375 °C. 相似文献
10.
This paper describes the experimental procedure to identify the predominant frequencies of the high speed testing machine
by conducting modal analysis. The effects due to the predominant frequencies of the system and loading rate on the magnitude
of system ringing and the flow stress were analyzed by using a single degree-of-freedom (SDOF) spring-mass-damper model. The
system was then used to study the dynamic tensile behavior of two engineering materials, i.e., polyethylene (PE) fabric-cement
composite and Alkaline Resistant (AR) glass fabrics at an intermediate strain rate. The stress oscillations in the response
of these materials due to system ringing were addressed. The failure behavior of each material was studied by examining high
speed digital camera images of specimens during the test. The validity of the dynamic tensile tests was investigated by examining
the condition of dynamic stress equilibrium—a criterion used in split Hopkinson pressure bar (SHPB) tests. The results show
that the quantitative criterion for a valid SHPB test is also applicable to dynamic tensile tests of these materials at the
intermediate strain rate. 相似文献
11.
本文揭示了在实际应用中极端工况下齿轮油的润滑特性.为了测量在高接触压力和不同温度条件下齿轮油的成膜能力,制作了高精度的膜厚测量仪,采用相对光强法实现纳米级膜厚测量.试验中共采用了5种性质不同的齿轮油,在纯滚动条件下测量接触区的油膜厚度,结果表明:随着接触压力的升高油膜厚度明显降低,但压力对润滑状态影响不大;温度的改变不但能影响油膜厚度,对润滑状态的影响也很明显;GL-5 85W/190和GL-5 85W/90齿轮油在接触压力达3 GPa温度提高到120℃时仍能形成很厚的油膜,但其余3种润滑剂在极端工况下成膜能力不足.本文最后根据试验结果还提出了含有丰富添加剂的齿轮油润滑模型. 相似文献
12.
Dynamic compressive behavior of dry quartz sand (Quikrete #1961 sand quarried in Pensacola, FL) under confinement was characterized
using a modified long split Hopkinson pressure bar (SHPB). Sand grains were confined inside a hollow cylinder of hardened
steel and capped by cemented tungsten carbide cylindrical rods. This assembly was subjected to repeated shaking to consolidate
sand to attain precise bulk mass densities. It is then sandwiched between incident and transmission bars on SHPB for dynamic
compression measurements. Sand specimens of five initial mass densities, namely, 1.51, 1.57, 1.63, 1.69, and 1.75 g/cm3, were characterized at high strain rates near 600 s−1, to determine the volumetric and deviatoric behaviors through measurements of both axial and transverse responses of a cylindrical
sand sample under confinement. The stress–strain relationship was found to follow a power law relationship with the sand initial
bulk density, with an exponent of 8.25, indicating a behavior highly sensitive to mass density. The energy absorption density
and compressibility of sand were determined as a function of axial stress. 相似文献
13.
High temperature (298 K–573 K) and high strain rate (4000 s−1) compression experiments were performed on a cryomilled ultra-fine grained (UFG) Al-5083 using a modified Kolsky bar with
a heating system designed to reduce “cold contact” time. The resulting stress strain curves show a reduction in strength of
approximately 300 MPa at the highest temperature tested. This softening has been related to a thermally activated deformation
mechanism. In addition, an experimental procedure was developed to investigate the microstructure evolution during the preheating,
prior to mechanical loading, so as to identify the intrinsic mechanical response of the material at high temperatures. The
results of this procedure are in good agreement with a TEM study on material that has been heated but not loaded. 相似文献
14.
PMMA低、中应变率单向拉伸力学性能的实验研究 总被引:8,自引:0,他引:8
利用MTS810试验机和自行研制的中应变率材料试验机对有机玻璃(PMMA)准静态(应变率为2.00×10-2s-1,2.01×10-3s-1和2.38×10-4s-1)和中应变率(应变率为18.6s-1,2.81s-1,6.54×10-1s-1和2.92×10-1s-1)单向拉伸力学性能进行了实验研究。应变率为2.38×10-4s-1时,应力-应变曲线中存在软化段。结果显示,在上述应变率范围内,PMMA的力学性能具有明显的应变率相关性,表现为应变率强化、应变率硬化和高速脆性。PMMA的拉伸力学性能在应变率达到18.6s-1时出现了更大的应变率敏感性。采用包含一个非线性弹簧和六个松弛模式的粘弹性模型分析PMMA力学性能的应变率相关性,得到PMMA在低、中应变率下单向拉伸的本构方程,理论结果与实验结果符合较好。 相似文献
15.
电子器件中大量使用铜膜作为电信号通道,而且一般采用电镀工艺制成.铜膜的力学性能参数对于其热疲劳可靠性的研究非常重要.目前有关该材料的力学性能研究尚不充分,而且数据极为不统一.本文借助于纳米压痕法、声发射等实验手段对电镀铜薄膜的静态力学性能(包括弹性模量和屈服强度等)及疲劳性能进行了测试.结果发现,与大块铜材料相比,电镀铜薄膜的弹性模量低很多,但屈服强度与大块铜材料相当,甚至高出200%.同时,本文采用弯曲疲劳实验,以电阻变化为失效判据,对镀铜材料的疲劳性能进行了测试,获取了该材料不同失效判据下的疲劳寿命预测模型的系数. 相似文献
16.
17.
This work presents an original broadband method able to determine the homogenized mechanical properties of orthotropic composite plates in their main directions. This method is based on a vibratory inverse method and do not need using Eigen mode. This technique is derived from the Force Analysis Technique (FAT), originally designed to identify vibration sources on bars and plates. The main advantage of this method is that it does not require any specific preparation and can be carried out on a real and complex structure. Moreover it is non-destructive and non-invasive method and only requires the excitation by a classical electromagnetic shaker. The main characteristic mechanical parameters (Young’s moduli and damping loss factors) are identified at all measured frequencies and not only at the Eigen frequencies as compared to others measurement techniques. An experimental validation shows a good correlation with the expected values for the Young’s moduli of the test plate. Working on a complex structure shows that the method is applicable for various configurations of operating conditions and leads to a good determination of the mechanical properties of a planar component. 相似文献
18.
M. Hokka J. Kokkonen J. Seidt T. Matrka A. Gilat V.-T. Kuokkala 《Experimental Mechanics》2012,52(2):195-203
Mechanical properties of most metallic materials can be improved by reducing their grain size. One of the methods used to
reduce the grain size even to the nanometer level is the severe plastic deformation processing. Equal Channel Angular Pressing
(ECAP) is one of the most promising severe plastic deformation processes for the nanocrystallization of ductile metals. Nanocrystalline
and ultrafine grained metals usually have significantly higher strength properties but lower tensile ductility compared to
the coarse grained metals. In this work, the torsion properties of ECAP processed ultrafine grained pure 1070 aluminum were
studied in a wide range of strain rates using both servohydraulic materials testing machines and Hopkinson Split Bar techniques.
The material exhibits extremely high ductility in torsion and the specimens did not fail even after 300% of strain. Pronounced
yield point behavior was observed at strain rates 500 s−1 and higher, whereas at lower strain rates the yielding was continuous. The material showed slight strain softening at the
strain rate of 10−4 s−1, almost ideally plastic behavior at strain rates between 10−3 s−1 and 500 s−1, and slight but increasing strain hardening at strain rates higher than that. The tests were monitored using digital cameras,
and the strain distributions on the surface of the specimens were calculated using digital image correlation. The strain in
the specimen localized very rapidly after yielding at all strain rates, and the localization lead to the development of a
shear band. At high strain rates the shear band developed faster than at low strain rates. 相似文献
19.
An innovative identification strategy based on high power ultrasonic loading together with both infrared thermography and ultra-high speed imaging is presented in this article. It was shown to be able to characterize the visco-elastic behaviour of a polymer specimen (PMMA) from a single sample over a range of temperatures and strain-rates. The paper focuses on moderate strain-rates, i.e. from 10 to 200 s?1, and temperatures ranging from room to the material glass transition temperature, i.e. 110°C. The main originality lies in the fact that contrary to conventional Dynamic Mechanical Thermal Analysis (DMTA), no frequency or temperature sweep is required since the experiment is designed to simultaneously produce both a heterogeneous strain-rate state and a heterogeneous temperature state allowing a local and multi-parametric identification. This article is seminal in nature and the test presented here has good potential to tackle a range of other types of high strain-rate testing situations. 相似文献