Correction of higher mode Pochhammer–Chree dispersion in experimental blast loading measurements

Barr, A.D.; Rigby, S.E.; Clayton, M.

doi:10.1016/j.ijimpeng.2020.103526

Cited by 11 publications

(13 citation statements)

References 26 publications

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“…in the region of Mach reflection. In a recent study, dispersion was shown to affect peak pressure recordings by up to 5% for normal reflection [47], and it is suggested that this loss could be greater for irregular/Mach reflection on account of the transient, high-frequency components of the Mach Stem.…”

Section: Comparison To Directly Measured Peak Pressuresmentioning

confidence: 99%

Reflected Near-field Blast Pressure Measurements Using High Speed Video

et al. 2020

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Background: The design and analysis of protective systems requires a detailed understanding of, and the ability to accurately predict, the distribution of pressure loads acting on an obstacle following an explosive detonation. In particular, there is a pressing need for accurate characterisation of blast loads in the region very close to a detonation, where even small improvised devices can produce serious structural or material damage. Objective: Accurate experimental measurement of these near-field blast events, using intrusive methods, is demanding owing to the high magnitudes (> 100 MPa) and short durations (< 1 ms) of loading. The objective of this article is to develop a non-intrusive method for measuring reflected blast pressure distributions using image analysis. Methods: This article presents results from high speed video analysis of nearfield spherical PE4 explosive blasts. The Canny edge detection algorithm is used to track the outer surface of the explosive fireball, with the results used to derive a velocity-radius relationship. Reflected pressure distributions are calculated using this velocity-radius relationship in conjunction with the Rankine-Hugoniot jump conditions. Results: The indirectly measured pressure distributions from high speed video are compared with directly measured pressure distributions and are shown to be in good qualitative agreement with respect to distribution of reflected pressures, and in good quantitative agreement with peak reflected pressures (within 10% of the maximum recorded value). Conclusions: The results indicate that it is possible to accurately measure blast loads in the order of 100s MPa using techniques which do not require sensitive recording equipment to be located close to the source of the explosion.

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Section: Comparison To Directly Measured Peak Pressuresmentioning

confidence: 99%

Reflected Near-field Blast Pressure Measurements Using High Speed Video

et al. 2020

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“…Precise calibration of the one-dimensional (1D) sound speed (c o ) and Poisson's ratio (ν) of a circular bar is essential in using the split Hopkinson bar (SHB) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and Hopkinson bar (HB) [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. In the case of SHB experiments, the specimen properties are generally determined using the following equations [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]:…”

Section: Introductionmentioning

confidence: 99%

“…2 Literature Survey 2.1 Dispersion Correction in Bar Technology. HB [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] has traditionally been used to measure a transient pulse generated by the impact of a near-field blast or bullets. Conversely, SHB, which is also called the Kolsky bar [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], has been used extensively to measure dynamic material properties such as the stress-strain and strain rate-strain curves of versatile materials at strain rates of approximately 10 2 -10 4 s −1 .…”

Section: Introductionmentioning

confidence: 99%

“…In the case of HB, the front surface of the bar is the location of interest where an impact pulse enters the bar, whereas the specimen location is of interest in the case of SHB. Therefore, the measured wave profile in SHB and HB needs to be corrected to obtain the wave profiles at the locations of interest, which is a process called dc [18,[27][28][29][30][55][56][57][58][59][60][61][62][63][64][65][66].…”

Section: Introductionmentioning

confidence: 99%

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Sound Speed and Poisson’s Ratio Calibration of (Split) Hopkinson Bar via Iterative Dispersion Correction of Elastic Wave

Shin

2022

Journal of Applied Mechanics

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A process of calibrating a one-dimensional sound speed (c_o) and Poisson's ratio (v) of a (split) Hopkinson bar is presented. This process consists of Fourier synthesis and iterative dispersion correction (time-domain phase shift) of the elastic pulse generated by the striker impact on a circular bar. At each iteration, a set of co and v is assumed, and the sound speed vs. frequency (c vs. f) relationship under the assumed set is obtained using the Pochhammer–Chree equation solver developed herein for ground state excitation. Subsequently, each constituting wave of the elastic pulse was phase-shifted (dispersion-corrected) using the c–f relationship. The co and v values of the bar were determined in the iteration process when the dispersion-corrected overall pulse profiles were reasonably consistent with the measured profiles at two travel distances in the bar. The observed consistency of the predicted (dispersion-corrected) wave profiles with the measured profiles is a mutually self-consistent verification of (i) the calibrated values of co and v, and (ii) the combined theories of Fourier and Pochhammer–Chree. The contributions of the calibrated values of co and v to contemporary bar technology are discussed, together with the physical significance of the tail part of a traveling wave according to the combined theories. A preprocessing template (in Excel®) and calibration platform (in MATLAB ®) for the presented calibration process are available online in a public repository.

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“…This leads to a phenomenon called dispersion, where the relative movement of these components results in a change in the shape of the signal between the face of the bar and the strain gauge location [ 21 ]. Techniques have been developed to account for the effects of dispersion in pressure bar signals [ 28 , 29 ], but limits on bandwidth are still imposed by the variation of stress over the bar cross section, and the occurrence of “nodal cylinders” on the bar surface at some frequencies, where zero axial strain is recorded on the bar surface despite a non-zero internal strain. One of the simplest ways to minimise dispersive and cross-sectional effects is by increasing the ratio of the signal wavelength to pressure bar radius, that is, using a smaller diameter pressure bar.…”

Section: Experimental Designmentioning

confidence: 99%

Temporally and Spatially Resolved Reflected Overpressure Measurements in the Extreme Near Field

Barr

Rigby

Clarke

et al. 2023

Sensors

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The design of blast-resistant structures and protective systems requires a firm understanding of the loadings imparted to structures by blast waves. While empirical methods can reliably predict these loadings in the far field, there is currently a lack of understanding on the pressures experienced in the very near field, where physics-based numerical modelling and semi-empirical fast-running engineering model predictions can vary by an order of magnitude. In this paper, we present the design of an experimental facility capable of providing definitive spatially and temporally resolved reflected pressure data in the extreme near field (Z<0.5 m/kg1/3). The Mechanisms and Characterisation of Explosions (MaCE) facility is a specific near-field evolution of the existing Characterisation of Blast Loading (CoBL) facility, which uses an array of Hopkinson pressure bars embedded in a stiff target plate. Maraging steel pressure bars and specially designed strain gauges are used to increase the measurement capacity from 600 MPa to 1800 MPa, and 33 pressure bars in a radial grid are used to improve the spatial resolution from 25 mm to 12.5 mm over the 100 mm radius measurement area. In addition, the pressure bar diameter is reduced from 10 mm to 4 mm, which greatly reduces stress wave dispersion, increasing the effective bandwidth. This enables the observation of high-frequency features in the pressure measurements, which is vital for validating the near-field transient effects predicted by numerical modelling and developing effective blast mitigation methods.

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Correction of higher mode Pochhammer–Chree dispersion in experimental blast loading measurements

Cited by 11 publications

References 26 publications

Reflected Near-field Blast Pressure Measurements Using High Speed Video

Reflected Near-field Blast Pressure Measurements Using High Speed Video

Sound Speed and Poisson’s Ratio Calibration of (Split) Hopkinson Bar via Iterative Dispersion Correction of Elastic Wave

Temporally and Spatially Resolved Reflected Overpressure Measurements in the Extreme Near Field

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