scholarly journals Local Phase-Amplitude Joint Correction for Free Surface Velocity of Hopkinson Pressure Bar

2020 ◽  
Vol 10 (15) ◽  
pp. 5390
Author(s):  
Jun Yang ◽  
Junhua He ◽  
Dezhi Zhang ◽  
Haibin Xu ◽  
Guokai Shi ◽  
...  
Keyword(s):  
Elastic Wave ◽  
Surface Velocity ◽  
Propagation Mode ◽  
Local Phase ◽  
Free Surface Velocity ◽  
Correction Algorithm ◽  
Hopkinson Pressure Bar ◽  
Phase Amplitude ◽  
Pressure Bar ◽  
The Impact

The Hopkinson pressure bar is widely used to measure the reflected pressure of blast waves over a short distance. However, dispersion effects will occur when the elastic stress waves propagate in the pressure bar due to lateral inertia, and there will be errors between the signals obtained from the sensors and the actual loading. For the free surface velocity measured in our system, we developed a local phase-amplitude joint correction method to convert the measured velocity into the average reflected pressure of a shock wave at the impact end of the bar, considering factors such as propagation modes of the elastic wave, the frequency components’ time of arrival, velocity variation over the bar axis, and the stress–velocity relationship. Firstly, the Pochhammer–Chree frequency equation is calculated numerically, and the first to fourth orders of phase velocity, group velocity, normalized frequency, and propagation time curves of elastic wave propagation in 35CrMnSiA steel are obtained. Secondly, the phase and amplitude correction formulas for calculating average reflected pressure from center velocity are derived based on the propagation mode of the axial elastic wave in the pressure bar by analyzing the time-frequency combined spectrum obtained by short-time Fourier transform. Thirdly, a local phase-amplitude joint correction algorithm based on propagation mode is proposed in detail. The experimental tests and data analyses are carried out for eight sets of pressure bar. The results show that this method can identify the propagation mode of elastic waves in the bar intuitively and clearly. The first three orders of propagation modes are stimulated in the bar 04, while only the first order of propagation is stimulated in the other eight bars. The local phase-amplitude joint correction algorithm can avoid correcting the component of the non-axial elastic wave. The rising edge of the average stress curve on the impact surface of bar 01 and bar 04 is corrected from 4.13 μs and 4.09 μs to 2.70 μs, respectively.

Analysis of the Impact of the Frequency Range of the Tensometer Bridge and Projectile Geometry on the Results of Measurements by the Split Hopkinson Pressure Bar Method

2013 ◽  
Vol 20 (4) ◽  
pp. 555-564 ◽  
Author(s):  
Wojciech Moćko
Keyword(s):  
Test Bench ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Deformation ◽  
Spectral Width ◽  
Hopkinson Pressure Bar ◽  
Computing Environment ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
The Impact ◽  
Bench Model

Abstract The paper presents the results of the analysis of the striker shape impact on the shape of the mechanical elastic wave generated in the Hopkinson bar. The influence of the tensometer amplifier bandwidth on the stress-strain characteristics obtained in this method was analyzed too. For the purposes of analyzing under the computing environment ABAQUS / Explicit the test bench model was created, and then the analysis of the process of dynamic deformation of the specimen with specific mechanical parameters was carried out. Based on those tests, it was found that the geometry of the end of the striker has an effect on the form of the loading wave and the spectral width of the signal of that wave. Reduction of the striker end diameter reduces unwanted oscillations, however, adversely affects the time of strain rate stabilization. It was determined for the assumed test bench configuration that a tensometric measurement system with a bandwidth equal to 50 kHz is sufficient

scholarly journals On backward dispersion correction of Hopkinson pressure bar signals

2014 ◽  
Vol 372 (2023) ◽  
pp. 20130291 ◽  
Author(s):  
A. Tyas ◽  
Z. Ozdemir
Keyword(s):  
Impact Load ◽  
Wide Spectrum ◽  
Accurate Determination ◽  
Experimental Studies ◽  
Dispersion Correction ◽  
Impact Event ◽  
Hopkinson Pressure Bar ◽  
Phase Velocity Dispersion ◽  
Pressure Bar ◽  
The Impact

Elastic theory shows that wide spectrum signals in the Hopkinson pressure bar suffer two forms of distortion as they propagate from the loaded bar face. These must be accounted for if accurate determination of the impact load is to be possible. The first form of distortion is the well-known phase velocity dispersion effect. The second form, which can be equally deleterious, is the prediction that at high frequencies, the stress and strain generated in the bar varies with radial position on the cross section, even for a uniformly applied loading. We consider the consequences of these effects on our ability to conduct accurate backward dispersion correction of bar signals, that is, to derive the impact face load from the dispersed signal recorded at some other point on the bar. We conclude that there is an upper limit on the frequency for which the distortion effects can be accurately compensated, and that this can significantly affect the accuracy of experimental results. We propose a combination of experimental studies and detailed numerical modelling of the impact event and wave propagation along the bar to gain better understanding of the frequency content of the impact event, and help assess the accuracy of experimental predictions of impact face load.

Wave Propagation in the Split Hopkinson Pressure Bar

1983 ◽  
Vol 105 (1) ◽  
pp. 61-66 ◽  
Author(s):  
P. S. Follansbee ◽  
C. Frantz
Keyword(s):  
Wave Propagation ◽  
Elastic Wave ◽  
Split Hopkinson Pressure Bar ◽  
Strain Curve ◽  
Leading Edge ◽  
Elastic Wave Propagation ◽  
Mathematical Treatment ◽  
Hopkinson Pressure Bar ◽  
Split Hopkinson ◽  
Pressure Bar

Elastic wave propagation in the split Hopkinson pressure bar (SHPB) is discussed with an emphasis on the origin and nature of the oscillations that often trail the leading edge of the pressure wave. We show that in the conditions of the SHPB test the pressure bars vibrate in the fundamental mode and that elastic wave propagation can be fully described mathematically. Excellent agreement is found between experimental results and predictions of the mathematical treatment. This suggests that dispersion effects in the pressure bars can be removed from the strain gage records, which reduces the magnitude of the oscillations in the resulting stress strain curve.

Experimental Study of Impact Strength of Al-6063 Alloy Processed by Equal Channel Angular Extrusion

2014 ◽  
Vol 911 ◽  
pp. 158-162 ◽  
Author(s):  
Shamsuddin Sulaiman ◽  
J. Nemati ◽  
Hani Mizhir Magid ◽  
B.T.H.T. Baharudin ◽  
G.H. Majzoobi ◽  
...  
Keyword(s):  
Impact Strength ◽  
Equal Channel Angular Extrusion ◽  
Split Hopkinson Pressure Bar ◽  
Hopkinson Pressure Bar ◽  
Angular Extrusion ◽  
Split Hopkinson ◽  
Ram Speed ◽  
Pressure Bar ◽  
The Impact ◽  
Strength Improvement

In the present study, the impact strength of annealed Al-6063 alloy developed by equal channel angular extrusion (ECAE), up to 6 passes at a temperature of 200°C following route A with a constant ram speed of 30 mm/min through a die angle of 90° between the die channels was investigated. The impact strength of extruded specimens is evaluated for different passes at a strain rate of 1800 s-1 using Split-Hopkinson pressure bar techniques. The results indicate that the major strength improvement occurs in the 5th and 6th passes while in primary passes, the strength improved but at a considerably lower rate. A total increasing in ultimate strength (UTS) and yield strength (YS) are 127% and 65% respectively and observed for the extruded material after 6 passes. Optical microscopic examinations show a grain refinement from 45 μm to 2.8 μm.

scholarly journals Wave Attenuation and Dispersion in a 6 mm Diameter Viscoelastic Split Hopkinson Pressure Bar and Its Correction Method

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Haotian Zhang ◽  
Linjian Ma ◽  
Zongmu Luo ◽  
Ning Zhang
Keyword(s):  
Impact Velocity ◽  
Wave Attenuation ◽  
Split Hopkinson Pressure Bar ◽  
Small Diameter ◽  
Correction Method ◽  
Hopkinson Pressure Bar ◽  
Amplitude Attenuation ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
The Impact

The propagation characteristics of viscoelastic waves have been investigated with a 6 mm diameter split Hopkinson pressure bar (SHPB) made of polymethyl methacrylate (PMMA). The strain signals in SHPB tests were improved by the pulse shaping technique. Based on the experimentally determined propagation coefficients, the amplitude attenuation and wave dispersion induced by viscoelastic effects at different impact velocities were quantitatively analyzed. The results indicate that the high-frequency harmonics attenuate faster in a higher phase velocity. With an increase in the impact velocity, the amplitude attenuation of the viscoelastic wave changes slightly during propagation, while the waveform dispersion gradually intensifies. A feasible method by waveform prediction was proposed to verify the validity and applicability of the propagation coefficient. The results indicate that the strain obtained from the small diameter viscoelastic SHPB can be effectively modified by utilizing the propagation coefficient. Furthermore, it is preferred to adopt the propagation coefficient obtained at low impact velocity for correction when the impact velocity varies. Moreover, the PMMA-steel bar impact test was performed to further illustrate the accuracy of the propagation coefficient and the effectiveness of the correction method.

Impact Compressive Properties of Foamed Film with Closed Cell

2014 ◽  
Vol 566 ◽  
pp. 134-139 ◽  
Author(s):  
Hiroyuki Yamada ◽  
Ryo Okui ◽  
Nagahisa Ogasawara ◽  
Hidetoshi Kobayashi ◽  
Kinya Ogawa
Keyword(s):  
Strain Rate ◽  
Impact Test ◽  
Split Hopkinson Pressure Bar ◽  
Rate Dependency ◽  
Hopkinson Pressure Bar ◽  
Compressive Properties ◽  
Static Test ◽  
Closed Cell ◽  
Pressure Bar ◽  
The Impact

The compressive properties of foamed polyethylene (PE) film with a closed cell for electronic devices have been investigated. A commercial closed cell foamed PE film with a density of 330 kg/m3 was used. Quasi-static testing was carried out at strain rates of 10−3 to 10−1 s−1. The strain rate of the impact test was approximately 105 s−1 by means of split Hopkinson pressure bar method. Within the set of experiments, the compressive stress increased with the strain rate in both the quasi-static and impact test. In particular, the flow stress increased substantially with the increasing strain rate in the impact deformation. At strains of less than 0.4, the trapped air was locally compressed within the cells, which led to the strain rate dependency of strength in the quasi-static test and the impact test.

scholarly journals Experiments with the Hopkinson pressure bar

1923 ◽  
Vol 103 (723) ◽  
pp. 622-643 ◽  
Keyword(s):  
Royal Society ◽  
Hopkinson Pressure Bar ◽  
High Explosives ◽  
Late Professor ◽  
Pressure Bar ◽  
The Impact ◽  
Royal Society Of London

In November, 1913, the late Professor Bertram Hopkinson read a paper before the Royal Society entitled “ A method of measuring the Pressure produced in the Detonation of High Explosives or by the Impact of Bullets.” (‘ Phil. Trans.,’ Royal Society of London. Series A, vol. 213 ; and Collected Papers, p. 438.) After this paper further experiments with gun-cotton were made by one of us, who was assistant to Prof. Hopkinson, and these were continued until the beginning of the War in 1914. During this time very numerous results were collected, but unfortunately these had not received the consideration or criticism of Prof. Hopkinson at the time of his death.

scholarly journals Research On Water-Immersion Softening Mechanism of Coal Rock Mass Based on Split Hopkinson Pressure Bar Experiment

2021 ◽  
Author(s):  
Zhiyuan Liu ◽  
Gang Wang ◽  
Jinzhou Li ◽  
Huaixing Li ◽  
Haifeng Zhao ◽  
...  
Keyword(s):  
Moisture Content ◽  
Coal Sample ◽  
Split Hopkinson Pressure Bar ◽  
Water Immersion ◽  
Compression Tests ◽  
Hopkinson Pressure Bar ◽  
Impact Compression ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
The Impact

Abstract The coal mining process is affected by multiple sources of water such as groundwater and coal seam water injection. Understanding the dynamic mechanical parameters of water-immersed coal is helpful to the safe production of coal mines. The impact compression tests were performed on coal with different moisture contents by using the ϕ50 mm Split Hopkinson Pressure Bar (SHPB) experimental system, and the dynamic characteristics and energy loss laws of water-immersed coal with different compositions and water contents were analyzed. Through analysis and discussion, it is found that: (1) When the moisture content of the coal sample is 0%, 30%, 60%, the stress, strain rate and energy first increase and then decrease with time; (2) When the moisture content of the coal sample increases from 30% to 60%, the stress "plateau" of the coal sample disappears, resulting in an increase in the interval of the compressive stress and a decrease in the interval of the expansion stress. (3) The increase of the moisture content of the coal sample will affect its impact deformation and failure mode. When the moisture content is 60%, the incident rod end and the transmission rod end of the coal sample will have obvious compression failure, and the middle part of the coal sample will also experience expansion and deformation. (4) The coal composition ratio suitable for the impact experiment of coal immersion softening is optimized.

An Experimental Surface-Wave Method for Recording Force-Time Curves in Elastic Impacts

1959 ◽  
Vol 26 (1) ◽  
pp. 3-7
Author(s):  
J. N. Goodier ◽  
W. E. Jahsman ◽  
E. A. Ripperger
Keyword(s):  
Surface Wave ◽  
Plane Surface ◽  
Hopkinson Pressure Bar ◽  
Time Curve ◽  
Experimental Surface ◽  
Force Time ◽  
Steel Balls ◽  
Pressure Bar ◽  
Surface Wave Method ◽  
The Impact

Abstract The recording of impacts by means of the longitudinal strain wave generated in a Hopkinson pressure bar is no longer possible when the impact is very brief, on account of dispersive effects. The Rayleigh surface wave generated on the plane surface of a block is nondispersive. A method is given for deducing the force-time curve of the impact from the oscilloscope record of the surface wave, and applied to impacts of small steel balls on a block.

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