Hydraulic Testing of Ordnance Components

[+] Author and Article Information
Tony D. Andrews

 QinetiQ, Cody Technology Park, Ively Road, Farnborough, Hampshire GU14 0LX, UKtdandrews@qinetiq.com

Fred E. Brine

 QinetiQ, Cody Technology Park, Ively Road, Farnborough, Hampshire GU14 0LX, UK

J. Pressure Vessel Technol 128(2), 162-167 (Jan 03, 2006) (6 pages) doi:10.1115/1.2179433 History: Received December 06, 2005; Revised January 03, 2006

This paper describes a range of hydraulic fatigue and pressure tests carried out on gun barrels and ordnance components in support of weapons research and development programs. Cyclic testing of representative sections of large caliber guns has been routinely carried out to determine safe fatigue life for operational use. Ultrasonic techniques have been developed for mapping multiple cracks within the gun barrels by which periodic examinations of barrels during testing have been used to build up histories of crack initiation and growth. In relatively unworn barrels multiple cracks, initiated along each rifling groove, are shown to form in an extremely stable array that can grow to several millimeters depth, in agreement with calculated stress intensity factors, before one crack accelerates to dominate final failure. The development of localized erosion from extensive firing is shown to significantly affect the subsequent hydraulic fatigue cycling by generation of only one or two cracks as well as the prior removal of heavily prestressed bore material. Tests on fume extractor sections of barrels show that cracking initiates in the jet holes and only grows to the bore at late stages. Introduction of different levels of autofrettage acts to bias the radial location of the cracks. An extensive experimental program of work has been carried out in support of design studies on mid-wall cooled gun barrels exploring a number of different configurations for construction of compound tubes and the results of numerical simulations of the assembly process have been compared with strain gauge measurements during the experimental procedure on scale tubes. Subsequent hydraulic cycling was used to determine the fatigue implications of the processing route.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Fragment from failure of 155mm barrel during firing

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Figure 2

Hydraulic fatigue test apparatus

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Figure 3

Crack map after 12,000cycles (first cracks detected)

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Figure 4

Crack map after 19,500cycles (just prior to fracture)

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Figure 5

Air melt non-autofrettaged barrel

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Figure 6

Autofrettaged barrel

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Figure 7

Typical external failure appearance

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Figure 8

Effect of erosion on hydraulic fatigue life

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Figure 9

Residual life for given erosion+crack depth

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Figure 10

Fatigue cracking in gun barrel section

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Figure 11

Calculated stress intensity factors for equally spaced arrays of cracks

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Figure 12

Calculated and measured crack depths

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Figure 13

Fatigue test comparison with failure during firing

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Figure 14

Good quality material: 30,000cycles to failure

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Figure 15

Poor quality material: 400cycles to failure

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Figure 16

Assembly for fatigue test of fume extractor

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Figure 17

Cracking from jet holes after testing

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Figure 18

Compound tubes prior to pressurization

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Figure 19

Tube prepared for assembly

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Figure 20

Strain gauge results during pressurization of tube

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Figure 21

Fracture of fatigued barrel sections




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