The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Han Zhao - One of the best experts on this subject based on the ideXlab platform.
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A versatile split Hopkinson Pressure Bar using electromagnetic loading
International Journal of Impact Engineering, 2018Co-Authors: Beibei Wu, Yulong Li, Han ZhaoAbstract:Abstract This paper presents a novel electromagnetic split Hopkinson Pressure Bar (ESHPB), which employs the electromagnetic energy conversion technique of LC circuit to generate directly the incident stress pulse. Such a versatile technique can generate easily compressive as well as tensile incident pulses. The duration and amplitude of the incident pulse could be controlled by adjusting the capacitance and charging voltage in the LC circuit. Therefore, compressive or tensile high strain-rate tests can easily be performed using the present apparatus by simply choosing the compression Bars or tension Bars. The primitive shape of generated stress pulse is a half-sine function, which is well suited for testing brittle materials and soft rubber-like materials in order to reach a rather constant strain rate. Meanwhile, for the tests of metals, a pulse shaper can be used to reach a rather classical trapezoidal pulse similar to that of the classical Pressure Bar tests. Furthermore, it is also possible to modify the stress pulse by shaping the discharge current using a specially designed active coil array and a sequential switch. Finally, a number of different materials were tested in compression and tension using this electromagnetic split Hopkinson Bar system. The same materials were also tested using the traditional split Hopkinson Bars. It turns out that the results obtained by the present device are consistent with those by the traditional split Hopkinson Bars. Compared with traditional pulse generation techniques by the impact of a projectile or by a sudden release of a pre-stressed section, the proposed electromagnetic energy conversion technique can be accurately triggered within several microseconds. It is, therefore, a good candidate to supply the symmetrical and synchronous loads in bidirectional or biaxial split Hopkinson Bar systems in the future.
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On the use of a viscoelastic split Hopkinson Pressure Bar
International Journal of Impact Engineering, 1997Co-Authors: Han Zhao, G. Gary, J. R. KlepaczkoAbstract:To test weak materials such as foams at high strain rates, the use of a Split Hopkinson Pressure Bar (SHPB) setup made of low impedance Bars, which are mostly viscoelastic, is indispensable. In this paper a detailed study of the technical problems of such a viscoelastic setup related to the measurement and to the loading conditions is offered. On the basis of the three-dimensional (3D) Fourier stationary harmonic wave analysis, the wave shifting technique is developed. It is shown that the effect of geometrical dispersion in a viscoelastic setup is generally non-negligible. The case of loading with a viscoelastic projectile is also analysed, showing that the impact of a viscoelastic projectile creates an incident wave with a significant time extension.
Weinong Chen - One of the best experts on this subject based on the ideXlab platform.
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shock testing accelerometers with a hopkinson Pressure Bar
International Journal of Impact Engineering, 2012Co-Authors: John T Foster, D J Frew, M J Forrestal, Erik E Nishida, Weinong ChenAbstract:The electronic industry continues to dramatically reduce the size of electrical components. Many of these components are now small enough to allow shock testing with Hopkinson Pressure Bar techniques. However, conventional Hopkinson Bar techniques must be modified to provide a broad array of shock pulse amplitudes and durations. For this study, we evaluate the shock response of accelerometers that measure large amplitude pulses, such as those experienced in projectile perforation and penetration tests. In particular, we modified the conventional Hopkinson Bar apparatus to produce relatively long duration pulses. The modified apparatus consists of a steel striker Bar, annealed copper pulse shapers, an aluminum incident Bar, and a tungsten disk with mounted accelerometers. With these modifications, we obtained accelerations pulses that reached amplitudes of 10 kG and durations of 0.5ms. To evaluate the performance of the accelerometers, acceleration-time responses are compared with models that use independent stress and strain measurements. Comparisons of data from all three measurements are in good agreement.
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upper limit of constant strain rates in a split hopkinson Pressure Bar experiment with elastic specimens
Experimental Mechanics, 2005Co-Authors: Yi Pan, Weinong Chen, B SongAbstract: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.
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split hopkinson Pressure Bar techniques for characterizing soft materials
Latin American Journal of Solids and Structures, 2005Co-Authors: Bo Song, Weinong ChenAbstract:EFICIENT USAGE OF SOFT MATERIALS UNDER IMPACT LOADING CONDITIONS REQUIRES ACCURATE AND RELIABLE DESCRIPTIONS OF THE HIGH-RATE MECHANICAL RESPONSES OF SUCH MATERIALS, WHICH MOTIVATES RECENT DEVELOPMENT OF VALID AND E±CIENT DYNAMIC EXPERIMENTAL TECHNIQUES. SPLIT HOPKINSON Pressure Bar (SHPB) HAS BEEN EXTENSIVELY USED TO CHARACTERIZE DYNAMIC BEHAVIOR OF METALLIC MATERIALS, BUT LESS FOR SOFT MATERIALS BECAUSE OF EXPERIMENTAL UNCERTAINTIES ASSOCIATED WITH SOFT MATERIAL CHARACTERIZATION. THIS PAPER FIRST PRESENTS MAJOR CHALLENGES ENCOUNTERED IN HOPKINSON Bar EXPERIMENTS ON SOFT MATERIALS, INCLUDING WEAK TRANSMITTED SIGNALS, DYNAMIC STRESS EQUILIBRIUM, AND CONSTANT STRAIN RATE, AND THEN SUMMARIZES RECENT RESEARCH E®ORTS IN THE MODIFICATIONS TO THE CONVENTIONAL SHPB FOR OBTAINING VALID AND ACCURATE STRESS-STRAIN DATA FOR SOFT MATERIALS.
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pulse shaping techniques for testing elastic plastic materials with a split hopkinson Pressure Bar
Experimental Mechanics, 2005Co-Authors: D J Frew, M J Forrestal, Weinong ChenAbstract: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.
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pulse shaping techniques for testing brittle materials with a split hopkinson Pressure Bar
Experimental Mechanics, 2002Co-Authors: D J Frew, M J Forrestal, Weinong ChenAbstract: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.
J. R. Klepaczko - One of the best experts on this subject based on the ideXlab platform.
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On the use of a viscoelastic split Hopkinson Pressure Bar
International Journal of Impact Engineering, 1997Co-Authors: Han Zhao, G. Gary, J. R. KlepaczkoAbstract:To test weak materials such as foams at high strain rates, the use of a Split Hopkinson Pressure Bar (SHPB) setup made of low impedance Bars, which are mostly viscoelastic, is indispensable. In this paper a detailed study of the technical problems of such a viscoelastic setup related to the measurement and to the loading conditions is offered. On the basis of the three-dimensional (3D) Fourier stationary harmonic wave analysis, the wave shifting technique is developed. It is shown that the effect of geometrical dispersion in a viscoelastic setup is generally non-negligible. The case of loading with a viscoelastic projectile is also analysed, showing that the impact of a viscoelastic projectile creates an incident wave with a significant time extension.
J. G. Williams - One of the best experts on this subject based on the ideXlab platform.
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Stress wave propagation effects in split Hopkinson Pressure Bar tests
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 1995Co-Authors: N. N. Dioh, Alojz Ivankovic, P. S. Leevers, J. G. WilliamsAbstract:Studies of the properties of materials at high strain rates by the split Hopkinson Pressure Bar suggest that most materials show a sharp increase in strain rate sensitivity at high rates. In this paper, analytical and numerical evidence is presented which shows that his apparent increase in the strain rate sensitivity reported in the literature may result from stress wave propagation effects present in the test. A one-dimensional analytical solution has been developed for a rate independent bi-linear material tested in a split Hopkinson Pressure Bar apparatus. The solution, which is based on a stress wave reverberation model, shows that there is an apparent increase in the strain rate sensitivity of the material which can only be explained in terms of large propagating plastic wave fronts in the specimen. Numerical modelling of the same test geometry for the same input material model is in excellent agreement showing conclusively that stress wave propagation effects are inevitable at high impact velocities. The assumption of uniform stress and strain distribution within a split Hopkinson Pressure Bar specimen is therefore incorrect at high impact velocities. The formulation of the novel numerical code used in the present work, which is based on the finite volume technique, is also presented.
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Thickness effects in split Hopkinson Pressure Bar tests
Polymer, 1993Co-Authors: N. N. Dioh, P. S. Leevers, J. G. WilliamsAbstract:Abstract Results are presented for the high strain rate behaviour of a medium and high density polyethylene, polycarbonate and poly(ether ether ketone) in compression for strain rates up to 104s−1 obtained using a split Hopkinson Pressure Bar apparatus. It is shown that the choice of specimen thickness in these tests significantly affects the measured flow stresses at high strain rates, with the thicker specimens showing an apparent enhancement of flow stress at high rates. Comparison of the present results with published work suggests that some high strain rate data in the literature could be erroneous due to an inappropriate choice of specimen dimensions.
Wang Hong - One of the best experts on this subject based on the ideXlab platform.
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the effect of the back front drafting zone Pressure Bar on the evenness of polyester cotton blend yarn
Progress in Textile Science & Technology, 2011Co-Authors: Wang HongAbstract:The yarn evenness in spinning is mainly from the drafting zone.Spinning test was compared through changing gauge block,back drafting times,back district roller center distance,etc.,when Pressure Bar in the draft zone was Pressured or not.The influences of Pressure Bar on the yarn evenness were analyzed and the ideal process configuration was obtained.
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The Effect of the Back-Front Drafting Zone Pressure Bar on the Evenness of Polyester/Cotton Blend Yarn
Progress in Textile Science & Technology, 2011Co-Authors: Wang HongAbstract:The yarn evenness in spinning is mainly from the drafting zone.Spinning test was compared through changing gauge block,back drafting times,back district roller center distance,etc.,when Pressure Bar in the draft zone was Pressured or not.The influences of Pressure Bar on the yarn evenness were analyzed and the ideal process configuration was obtained.
