Dynamic Failure Behavior of Polycrystalline Alumina Under Impact Loading

[+] Author and Article Information
Guowen Yao

School of Civil Engineering and Architecture, Chongqing Jiaotong University, Chongqing, 400074, China

Zhanfang Liu

Department of Engineering Mechanics, Chongqing University, Chongqing, 400044, China

J. Appl. Mech 74(5), 990-995 (Jan 07, 2007) (6 pages) doi:10.1115/1.2722777 History: Received February 14, 2006; Revised January 07, 2007

Plate impact experiments and impact recovery experiments were performed on 92.93wt.% aluminas using a 100mmdia compressed-gas gun. Free surface velocity histories were traced by a velocity interferometry system for any reflector (VISAR) velocity interferometer. There is a recompression signal in free surface velocity, which shows evidence of a failure wave in impacted alumina. The failure wave velocities are 1.27kms and 1.46kms at stresses of 7.54GPa and 8.56GPa, respectively. It drops to 0.21kms after the material released. SEM analysis of recovered samples showed the transit of intergranular microcracks to transgranular microcracks with increasing shock loading. A failure wave in impacted ceramics is a continuous fracture zone, which may be associated with the damage accumulation process during the propagation of shock waves. Then a progressive fracture model was proposed to describe the failure wave formation and propagation in shocked ceramics. The governing equation of the failure wave is characterized by inelastic bulk strain with material damage and fracture. Numerical simulation of the free surface velocity was performed in good agreement with the plate impact experiments. And the longitudinal, lateral, and shear stress histories upon the arrival of the failure wave were predicted, which present the diminished shear strength and lost spall strength in the failed layer.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Plate impact experimental schematic with VISAR

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Figure 2

Free surface velocity profiles showing small recompression for shots 405 and 425

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Figure 3

Free surface velocity profiles of glass monitored by VISAR (9,19-20)

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Figure 4

Propagation and interaction of compression, rarefaction and failure waves

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Figure 5

Expanded region of free surface velocity profile showing second small recompression signal from shot 425

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Figure 6

SEM micrographs of (a) initial and recovered alumina samples under (b) 5.76GPa, and (c) 8.65GPa shock loading

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Figure 7

Schematic of the failure wave and elastic precursor for the conservation of mass, momentum, and energy

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Figure 8

Free surface velocity histories of alumina specimens under shock loading

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Figure 9

Longitudinal, lateral, and shear stresses histories of specimens under shock loading simulated by progressive fracture model




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