A numerical investigation of dispersion in Hopkinson Pressure Bar experiments

Govender, Reuben; Cloete, T.J.; Nurick, G.N.

doi:10.1051/jp4:2006134080

Cited by 9 publications

(11 citation statements)

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“…While it is only possible to model an approximation of an infinitely-long pressure bar, the errors introduced by deviating from a true infinite bar can be minimised by windowing the forcing functions to reduce the inertial effects 1 introduced by the sudden application of stress at a free face [20,26], or by enforcing zero displacement boundary conditions for a small length of bar equal to the wavelength of the forcing function [28].…”

Section: Initial Considerationsmentioning

confidence: 99%

“…Representation of mass in either a lumped or consistent matrix will give rise to spurious oscillations [29], and the central-differencing explicit time-stepping algorithm used in most finite element solvers will give rise to oscillations that are indistinguishable from Pochhammer-Chree dispersion [28]. The results from a finite element model may therefore begin to diverge from theory, particularly when considering cumulative numerical losses associated with propagating higher frequencies (relative to mesh size) over long distances.…”

Section: Initial Considerationsmentioning

confidence: 99%

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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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Section: Initial Considerationsmentioning

confidence: 99%

Section: Initial Considerationsmentioning

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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“…The finite element modelling of Kolsky bar has been extensively reported in previous studies, e.g., for the determination of incident pulse shaping design [15,16], modelling of pulse shaper [17], for numerical verification of the apparatus design [18], misalignment effect in the loading bars [19], and investigation on wave dispersion in bars [20]. This study aims to provide comprehensive methodology to model elastomers in a Kolsky bar experiment with a focus on specimen geometry optimization, experimental verification, and pulse shaper geometry effect.…”

Section: Introductionmentioning

confidence: 99%

FE Analysis of Critical Testing Parameters in Kolsky Bar Experiments for Elastomers at High Strain Rate

Chaudhry

Czekanski

2019

Materials

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The main aim of this research is to present complete methodological guidelines for dynamic characterization of elastomers when subjected to strain rates of 100/s–10,000/s. We consider the following three aspects: (i) the design of high strain rate testing apparatus, (ii) finite element analysis for the optimization of the experimental setup, and (iii) experimental parameters and validation for the response of an elastomeric specimen. To test low impedance soft materials, design of a modified Kolsky bar is discussed. Based on this design, the testing apparatus was constructed, validated, and optimized numerically using finite element methods. Furthermore, investigations on traditional pulse shaping techniques and a new design for pulse shaper are described. The effect of specimen geometry on the homogeneous deformation has been thoroughly accounted for. Using the optimized specimen geometry and pulse shaping technique, nitrile butadiene rubber was tested at different strain rates, and the experimental findings were compared to numerical predictions.

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“…The Split Hopkinson Pressure Bar (SHPB) is the most widely used method to describe the results of different material samples exposed to medium and high speed shaping [26][27][28][29][30][31]. The best described SHPB process induces unidirectional pressure in the target sample by the simultaneous opposing impact of two bars.…”

Section: Materials Models For Virtual Ballistic Testingmentioning

confidence: 99%

Virtual Testing of Composite Structures Made of High Entropy Alloys and Steel

Geantă

Cherecheș²,

Lixandru³

et al. 2017

Metals

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High entropy alloys (HEA) are metallic materials obtained from a mixture of at least five atomic-scale chemical elements. They are characterized by high mechanical strength, good thermal stability and hardenability. AlCrFeCoNi alloys have high compression strength and tensile strength values of 2004 MPa, respectively 1250 MPa and elongation of about 32.7%. These materials can be used to create HEA-steel type composite structures which resist to dynamic deformation during high speed impacts. The paper presents four different composite structures made from a combination of HEA and carbon steel plates, using different joining processes. The numerical simulation of the impact behavior of the composite structures was performed by virtual methods, taking into account the mechanical properties of both materials. For analyzing each constructive variant, three virtual shootings were designed, using a 7.62 × 39 mm cal. incendiary armor-piercing bullet and different impact velocities. The best ballistic behavior was provided by the composite structures obtained by welding and brazing that have good continuity and rigidity. The other composite structures, which do not have good surface adhesion, show high fragmentation risk, because the rear plate can fragment on the axis of shooting due to the combination between the shock waves and the reflected ones. The order of materials in the composite structure has a very important role in decreasing the impact energy.

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A numerical investigation of dispersion in Hopkinson Pressure Bar experiments

Cited by 9 publications

References 0 publications

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

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

FE Analysis of Critical Testing Parameters in Kolsky Bar Experiments for Elastomers at High Strain Rate

Virtual Testing of Composite Structures Made of High Entropy Alloys and Steel

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