A review of Pochhammer–Chree dispersion in the Hopkinson bar

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

doi:10.1680/jencm.16.00027

Cited by 24 publications

(26 citation statements)

References 43 publications

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“…10a is likely due to a limitation of the HPB technique. Propagating pressure signals will exhibit a slight loss of definition of transient pressure features as a result of Pochhammer-Chree dispersion [45,46], and hence peak pressures recorded using the HPB technique may be a slight underestimation of the true peak reflected pressure at that angle of incidence, i.e. in the region of Mach reflection.…”

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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“…Dispersion effects can be seen to 'round off' the leading edge of the stress pulse, with the peak pressure in the central (0 mm) bar occurring on the second oscillation, rather than with arrival of the stress pulse as is the case with all other bars. Some higher frequency components of the signal (which travel at a lower velocity relative to the lower frequency components [54]) can be seen to arrive towards the end of the positive phase. Whilst this demonstrates that there may be significant high frequency features associated with the sharp rise of the pressure pulse, current frequency-domain dispersion correction methods are limited to frequencies of 250 kHz [55] for the bar radii used in this study.…”

Section: Direct Load Measurementsmentioning

confidence: 99%

Experimental Measurement of Specific Impulse Distribution and Transient Deformation of Plates Subjected to Near-Field Explosive Blasts

et al. 2018

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The shock wave generated from a high explosive detonation can cause significant damage to any objects that it encounters, particularly those objects located close to the source of the explosion. Understanding blast wave development and accurately quantifying its effect on structural systems remains a considerable challenge to the scientific community. This paper presents a comprehensive experimental study into the loading acting on, and subsequent deformation of, targets subjected to nearfield explosive detonations. Two experimental test series were conducted at the University of Sheffield (UoS), UK, and the University of Cape Town (UCT), South Africa, where blast load distributions using Hopkinson pressure bars and dynamic target deflections using digital image correlation were measured respectively. It is shown through conservation of momentum and Hopkinson-Cranz scaling that initial plate velocity profiles are directly proportional to the imparted impulse distribution, and that spatial variations in loading as a result of surface instabilities in the expanding detonation product cloud are significant enough to influence the transient displacement profile of a blast loaded plate.

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“…Dispersion of a stress wave is of particular concern in the measurement of explosive events, as it can result in the distortion or loss of important high-frequency features, impeding accurate quantification of the loading [14].…”

Section: Introductionmentioning

confidence: 99%

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

Barr

Rigby

Clayton

2020

International Journal of Impact Engineering

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Experimental measurements of blast loading using Hopkinson pressure bars are affected by dispersion which can result in the loss or distortion of important high-frequency features. Blast waves typically excite multiple modes of propagation in the bar, and full correction of dispersive effects is not currently possible as the magnitude of stress propagating in each mode is not known. In this paper we develop an algorithm for multiple mode dispersion correction based on rigorous interrogation of the results from a series of finite element analyses. First, a finite element model is validated against first-mode and higher-mode theory. The dispersion of short raised-cosine windowed pulses is then used to isolate the contribution of each propagating mode, enabling a relationship between frequency and modal apportioning of stress to be obtained for the first four propagating modes. Finally, four-mode dispersion correction is successfully applied to an experimental signal using an algorithm based on the derived relationships for modal apportioning. The four-mode results show significant improvement in the capture of high-frequency features over existing first-mode corrections, and demonstrate the potential of this method for the full correction of dispersion in experimental measurements of blast loading.

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A review of Pochhammer–Chree dispersion in the Hopkinson bar

Cited by 24 publications

References 43 publications

Reflected Near-field Blast Pressure Measurements Using High Speed Video

Reflected Near-field Blast Pressure Measurements Using High Speed Video

Experimental Measurement of Specific Impulse Distribution and Transient Deformation of Plates Subjected to Near-Field Explosive Blasts

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

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