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The influence of the counterfort while ballistic testing using gelatine blocks

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Abstract

In wound ballistic research, gelatine blocks of various dimensions are used depending on the simulated anatomical region. When relatively small blocks are used as substitute for a head, problems with regard to the expansion of the gelatine block could arise. The study was conducted to analyse the influence of the material the gelatine block is placed upon. Thirty-six shots were performed on 12 cm gelatine cubes doped with thin foil bags containing acrylic paint. Eighteen blocks each were placed on a rigid table or on a synthetic sponge of 5 cm height. Deforming bullets with different kinetic energies were fired from distance and recorded by a high-speed video camera. Subsequently, the gelatine cubes were cut into 1 cm thick slices which were scanned using a flatbed scanner. Cracks in the gelatine were analysed by measuring the longest crack, Fackler’s wound profile and the polygon (perimeter and area) outlining the ends of the cracks. The energy dissipated ranged from 153 to 707 J. For moderate energy transfer, no significant influence of the sustaining material was discerned. With increasing dissipated energy, the sponge was compressed correspondingly, and the cracks were longer than in gelatine blocks which had been placed on a table. High-speed video revealed a loss of symmetry and a flattened inferior margin of the temporary cavity with energies superior to approx. Two hundred Joules when the blocks were placed on a rigid platform. However, 12 cm gelatine cubes showed material limits by a non-linear response when more than 400 J were dissipated for both rigid and elastic sustainment. In conclusion, the smaller the gelatine blocks and the greater the energy transfers, the more important it is to take into account the counterfort of the sustaining material.

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Acknowledgments

This research work was funded by the SNF (Swiss National Science Foundation, project 310030E-147628/1). We wish to thank Michael Ziege and his colleagues (Grenzschutzgruppe 9, Federal Police, Hangelar, Germany) as well as Frank Gredig (Criminal Investigation Service, Police Department Bonn, Germany). The radiological assistance of Nicole Schwendener (Institute of Forensic Medicine Bern) is also gratefully acknowledged.

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Authors and Affiliations

  1. Institute of Forensic Medicine, University of Bern, Bühlstrasse 20, 3012, Bern, Switzerland

    C. Schyma, N. Herr, J. Brünig & E. Brenčičová

  2. Criminal Investigation Service of the Cantonal Police Department of Bern, Nordring 30, 3013, Bern, Switzerland

    R. Müller

Authors
  1. C. Schyma
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  2. N. Herr
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  3. J. Brünig
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  4. E. Brenčičová
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  5. R. Müller
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Correspondence to C. Schyma.

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Electronic supplementary material

Supplementary Figure 1

Gelatine cube placed on the sponge. Test shot using 9 mm Luger Gold Dot at the moment where the deformed bullet is still in sight. The maximal vertical extension of the temporary cavity is reached about 1.9 ms later. The images showing the arriving bullet were overlaid. (GIF 104 kb)

High resolution image (JPEG 161 kb)

Supplementary Figure 2

Slice in 8 cm depth of the bullet track (shot no. 15). Evaluation using the polygon method. The two longest cracks are measured and added (Fackler’s wound profile). The longest crack measures 27 mm (r max). The area of the polygon (PA) is 1138 mm2, the polygon perimeter (PP) is 131 mm. (GIF 100 kb)

High resolution image (JPEG 180 kb)

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Schyma, C., Herr, N., Brünig, J. et al. The influence of the counterfort while ballistic testing using gelatine blocks. Int J Legal Med 131, 1325–1332 (2017). https://doi.org/10.1007/s00414-017-1623-5

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  • DOI: https://doi.org/10.1007/s00414-017-1623-5

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