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Design and Analysis

Explosively Driven Fragmentation Experiments for Continuum Damage Modeling

[+] Author and Article Information
David E. Lambert

 Air Force Research Laboratory/Munitions Directorate, Eglin Air Force Base, FL 32542

John Osborn

 General Dynamics-Ordnance and Tactical Systems, Niceville, FL 32579

Michael V. Hopson

 Naval Surface Warfare Center, Dahlgren Division, Dahlgren, VA 22448

J. Pressure Vessel Technol 134(3), 031209 (May 18, 2012) (7 pages) doi:10.1115/1.4006119 History: Received February 08, 2011; Revised January 20, 2012; Published May 18, 2012; Online May 18, 2012

The explosively loaded right-circular tube geometry is used as the basis for dynamic fracture and fragmentation modeling. Details of the cylinder configuration are investigated to prescribe controlled loading conditions of uniaxial stress and plane strain. Earlier works by Goto [2008, “Investigation of the Fracture and Fragmentation of Explosively Driven Rings and Cylinders,” Int. J. Impact Eng. 35 (12), pp. 1547–1556] had used thin-walled tubes to provide plane strain loading and shorter “rings” to establish uniaxial stress conditions. This paper extends on that work to look at alternative cylinder dimensions and metals of interest. A tungsten alloy, Aero-224, and a high strength steel, Eglin Steel (ES-1), are the subject metals. Transient continuum-mechanics simulations evaluated whether the stress triaxiality conditions were being met as design parameters of cylinder material, cylinder wall-thickness, cylinder length, and initiation configuration were varied. Design analysis shows that the thin cylinders of ES-1 steel do establish the desired plane strain conditions as it expands to failure. Ultra-high speed photography experiments verify the time of fracture and correlate casewall expansion and velocity measurements. Synchronization of the code and diagnostics measurements is presented as a valuable analysis method. On the other hand, rings (i.e., uniaxial stress) of the Aero-224 tungsten alloy were failing just short of uniaxial stress approximating conditions. Analysis of the Aero-224 rings indicated it must be capable of achieving at least a 25% strain to failure in order to have the triaxiality condition satisfied. Strain to failure measurements directly from recovered fragments were less than 14%. Nevertheless, a Weibull distribution was fit to the empirical data set and used to drive a statistically compensated fracture model. Results and discussion of the failure strain distribution and the ability for continuum codes to adequately conduct such simulations are presented.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Cylinder of uniaxial stress (left 2) and plane strain stack of rings (right). Cu end sections provided clean boundary conditions for the central “specimen” sections.

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Figure 2

End-initiation of ES-1 cylinder at 5 μs (left), 20 μs (center), and 60 μs (right)

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Figure 3

Triaxiality response through ES-1 cylinder wall at a midplane position (10.1 cm from initiated end)

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Figure 4

Time dependent plastic strain of ES-1 cylinder

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Figure 5

Arrangement for short cylinder specimens

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Figure 6

Critical strain defined for short cylinder lengths

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Figure 7

Triaxiality of 0.40 cm ring of Aero-224, W-alloy

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Figure 8

ES-1 plane strain cylinder with PDV probes

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Figure 9

Plane strain cylinder fracture of ES-1 (colored lines relate to PDV data of Figs.  8910)

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Figure 10

PDV probe responses at locations 7.62, 10.16, and 12.70 cm from the cylinder end (plots are color-coded to Figs.  89)

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Figure 11

Cylinder before inserting into the foam cavity for water recovery

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Figure 12

Sample of Aero-224 recovered fragments

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Figure 13

Equivalent plastic strain, measured from Aero-224 fragments

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Figure 14

Lagrangian calculation of Aero-224 ring fragmentation

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Figure 15

Calculated fragment mass distributions

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