24th International Symposium on Ballistics 11

Authors: Paul Locking BAE Systems (Land)Dennis Flynn BAE Systems (Land) Jim Dunnett Fluid Gravity Engineering

Fluid Gravity Engineering

Warhead Filling and Casing Interactions affect the Blast Field performance

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Casing effects on Blast

ACKNOWLEDGEMENTS

This work was funded by the Weapon & Platform Effectors (WPE)Domain of the UK MoD Research Acquisition Office (RAO) andcontracted through QinetiQ, the Prime Contractor.

The authors are grateful for their kind permission to publish thiswork. RAO has since become the Defence Technology InnovationCentre (DTIC).

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Presentation Outline

Objectives

Historical Background

Recent Trials

Analysis

Conclusions

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Casing effects on Blast

Errata

I would like to apologise for one typographical error that gotthrough the proof reading:

Aluminium Alloy 6086T6

should read

Aluminium Alloy 6082 to Condition T6

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Objectives

Currently Engineering models predict Blast output from cased warheadsuse experimentally derived algorithms, e.g. Fano and Fisher curves

Such curves are typically based upon TNT explosive with the cast iron orsteel cases

Review Historical Data

Investigate

Ideal and Non-Ideal explosives Brittle and Ductile case materials

Integrated Trials and EDEN hydrocode Modelling to assess theseEngineering models

Establish a preferred model and its fit parameters with applicability foreach case

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Fisher EBC = C x [0.2 + 0.8/(1 + M/C)]Modified Fisher EBC = {C + C x [0.2 + 0.8/(1 + M/C)]}/2Fano EBC = C x [0.2 + 0.8/(1 + 2 x M/C)]Modified Fano EBC = C x [0.6 + 0.4/(1 + 2 x M/C)]Warren EBC = C x [0.4 + 0.6/(1 + 2 x M/C)]US for PressureEBC = 1.19 x C x [1 + M/C x (1 Mc)/(1 + M/C)]US for Impulse EBC = C x [1 + M/C x (1 Mc)/(1 + M/C)]

EBC = Equivalent Bare ChargeC = Charge massM = Mass of metal (in parallel section)Mc = M/C if M/C

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0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.1 1.0 10.0Case mass (M) / Charge mass (C)

Equi

vale

nt B

are

Cha

rge

(EB

C) Historic

Trials

Warren

Fisher

Fano

ModFano

EBC for Steel Casings

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Understanding Case Effects on Blast

Limited understanding of case effects Large scatter of trials data Wide choice of Engineering Models Limited data Need for updated trials with purpose made hardware and

extensive instrumentation With experimental controls Integrated EDEN hydrocode modelling Trials designed specifically for the hydrocode modelling

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Historic Trial Limitations / Unknowns

Explosive Type

Casing Material

Fragmentation Mechanism (Natural / Pre-fragmented)

Pressure or Impulse

Pressure Considered (Incident / Reflected)

Ground / Air

Shape (Spherical / Cylindrical)

Scaling

Confinement (Uniformly / Heavy Nose)

Initiation (Central / End)

Position / Aspect - Best historic trials gauge positions undefined

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Typical Issues that Arise

Angle of Incidence Range (R)

Record Reflected (Pr) pressure, but need to correct to get Incident (Pi) pressure, but its both Angle () and Pressure dependent

Reflected Pressure (Pr)

Ground or Wall

P P

t t

Shock WaveImpulse

Gauge at Angle

Incident Pressure (Pi)

in the Free Field

Gauge

Pr > Pi Pr = Cr . Pi

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