Research Papers

Crack Initiation and Growth in PBX 9502 High Explosive Subject to Compression

[+] Author and Article Information
C. Liu

Materials Science and Technology Division,
Los Alamos National Laboratory,
Los Alamos, NM 87545
e-mail: cliu@lanl.gov

D. G. Thompson

Weapons Experiments Division,
Los Alamos National Laboratory,
Los Alamos, NM 87545

1Corresponding author

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received June 11, 2014; final manuscript received July 21, 2014; accepted manuscript posted July 21, 2014; published online August 6, 2014. Editor: Yonggang Huang. By acceptance of this article, the publisher recognizes that the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for U.S. Government purposes.

J. Appl. Mech 81(10), 101004 (Aug 06, 2014) (13 pages) Paper No: JAM-14-1251; doi: 10.1115/1.4028087 History: Received June 11, 2014; Accepted July 21, 2014; Revised July 21, 2014

Brittle and quasi-brittle solids, when subject to compression, fail by the development of microcracks that originate from heterogeneity. Lateral confinement has been shown to affect the failure pattern of the testing specimen, from splitting type of cracking with no confinement, to failure by shear banding with moderate confinement, to plasticitylike ductile failure when subject to high confining pressure. Even in the case of simple uni-axial compression, near local heterogeneity, e.g., pore or a small crack, the nonuniform stress state will introduce local confinement. As a result, different types of failure can occur simultaneously. In the present study, we investigate the process of damage initiation, accumulation, and cracking in a specimen of plastic bonded explosive (PBX), PBX 9502, containing a cavity and subject to compression. Due to the nonuniform deformation near the cavity, both tensile cracks and shear-dominated widespread material damage are generated. Detailed variation of quantities that characterize the process of crack initiation and growth will be presented and discussed.

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Fig. 3

Overall response of specimen No. 2 (type A, test temperature of 50 °C)

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Fig. 4

Contour plots of the displacement field over the surface of specimen No. 2 at a selected moment of time indicated in Fig. 3: (a) displacement field in horizontal direction u and (b) displacement field in vertical direction v

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Fig. 2

(a) Variation of compressive load P as function of displacement δ of all PBX 9502 fracture tests. (b) Random speckle image of a PBX 9502 fracture specimen and the local measurement of displacement δ.

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Fig. 1

Perforated plate specimen for fracture experiment on PBX 9502 subject to compression. For type A specimen, d = 19.05 mm and for type B specimen, d = 25.4 mm.

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Fig. 5

Contour plots of the strain field, ɛx, ɛy, and ɛxy, at moment C indicated in Fig. 3, where δ∕H = 0.53%, of specimen No. 2 (type A, test temperature of 50 °C)

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Fig. 6

Contour plot of the correlation coefficient field, c, at moment D indicated in Fig. 3, where δ∕H = 0.84%, of specimen No. 2 (type A, test temperature of 50 °C)

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Fig. 11

Tensile crack growing histories of all specimens

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Fig. 7

(a) Description of cavity boundary with polar angle θ. (b) Variation of the correlation coefficient c along the cavity boundary.

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Fig. 8

Variation of the parameter cmax, over the cavity boundary, as a function of the overall deformation, δ∕H, for specimen No. 2

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Fig. 9

Contour plots of the correlation coefficient field at selected moments, indicated in Fig. 3, of specimen No. 2. The boundary of damage zones is shown as solid lines.

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Fig. 10

(a) Damage regions and tensile cracks in the PBX 9502 compression specimen. (b) Tensile crack growing history in specimen No. 2.

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Fig. 13

(a) Tensile cracks and crack-front coordinate. (b) Variation of strains in front of the tensile cracks.

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Fig. 12

(a) Critical overall compressive strain, ɛcrit, at crack initiation. (b) Crack initiation speed of all specimens.

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Fig. 14

Variation of crack-tip strain ɛx as function of overall deformation of the specimen δ∕H in specimen No. 8

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Fig. 15

Variation of crack-tip strain ɛx as function of overall deformation of the specimen δ∕H for (a) sample No. 2, (b) sample No.4, (c) sample No. 8, and (d) sample No. 10

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Fig. 16

Initiation tensile strain at notch tip

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Fig. 17

(a) Variation of total crack length L of specimen No. 2. (b) Variation of applied compressive stress σ as a function of normalized total crack length L/d of specimen No. 2.

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Fig. 19

Critical applied compressive stress σ at crack initiation

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Fig. 18

Variation of applied compressive stress σ as a function of normalized total crack length L/d of all specimens




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