Research Papers

Blast Wave Loading Pathways in Heterogeneous Material Systems–Experimental and Numerical Approaches

[+] Author and Article Information
Veera Selvan

Graduate Research Assistant
e-mail: veera_1431@yahoo.co.in

Shailesh Ganpule

Graduate Research Assistant
e-mail: shailesh@huskers.unl.edu

Nick Kleinschmit

Graduate Research Assistant
e-mail: n_kleinschmit@yahoo.com

Namas Chandra

Fellow, ASME
e-mail: nchandra2@unl.edu
Department of Mechanical and Materials Engineering,
University of Nebraska-Lincoln,
Lincoln, NE 68588-0656

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received May 19, 2012; final manuscript received March 16, 2013; accepted manuscript posted April 4, 2013; published online May 9, 2013. Assoc. Editor: Fotis Sotiropoulos.

J Biomech Eng 135(6), 061002 (May 09, 2013) (14 pages) Paper No: BIO-12-1198; doi: 10.1115/1.4024132 History: Received May 19, 2012; Revised March 16, 2013; Accepted April 04, 2013

Blast waves generated in the field explosions impinge on the head-brain complex and induce mechanical pressure pulses in the brain resulting in traumatic brain injury. Severity of the brain injury (mild to moderate to severe) is dependent upon the magnitude and duration of the pressure pulse, which in turn depends on the intensity and duration of the oncoming blast wave. A fluid-filled cylinder is idealized to represent the head-brain complex in its simplest form; the cylinder is experimentally subjected to an air blast of Friedlander type, and the temporal variations of cylinder surface pressures and strains and fluid pressures are measured. Based on these measured data and results from computational simulations, the mechanical loading pathways from the external blast to the pressure field in the fluid are identified; it is hypothesized that the net loading at a given material point in the fluid comprises direct transmissive loads and deflection-induced indirect loads. Parametric studies show that the acoustic impedance mismatches between the cylinder and the contained fluid as well as the flexural rigidity of the cylinder determine the shape/intensity of pressure pulses in the fluid.

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Fig. 1

Blast wave interaction with heterogeneous body: (a) and (e) are the schematic diagrams of the loading; (b) and (f) are direct loadings; (c), (d), (g), (h) are indirect loadings

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Fig. 2

(a) A 229 mm × 229 mm steel square-12 m long shock tube used in the experiments; (b) Fluid-filled cylinder inside the test section; (c) Cylindrical system with top and bottom sliders; (d) Cylinder (without fluid for clarity) showing the surface mount pressure/strain gauges on the cylinders and pressure probe mounts in the fluid

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Fig. 3

(a) Schematics of the experimental cylindrical setup; (b) Sectional view A-A showing all the sensor locations (c) Sensor type/location terminology: First letter-F=front, M=middle, B=back; Second number-1=outside, 2=inside; Third letter-P=air surface pressure or fluid probe pressure, S=surface mounted strain gauge

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Fig. 4

(a) FE discretization; (b) Loading and boundary conditions employed in the simulation

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Fig. 5

Experimental measurements at various locations (a) schematic view of measurement locations; (b) external blast overpressures; (c) cylindrical shell strain; (d) pressure pulse in the fluid

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Fig. 6

Comparison of experimental and numerical blast pressures at three locations: (a) schematic; (b) front; (c) middle; (d) back

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Fig. 7

Comparison of experimental and numerical shell strains at three locations: (a) shape change of the cylinder from circle to ellipse obtained from simulation (b) front; (c) middle; and (d) back

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Fig. 8

Comparison of experimental and numerical simulation results at three locations inside the fluid: (a) schematics; (b) front; (c) middle-notice the pressure oscillations (t=1.5–2 ms) corresponding to the round trip wave motion; and (d) back

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Fig. 9

Numerical simulations of pressure pulse: Top row- 2 mm polycarbonate/steel; Bottom row-7 mm polycarbonate/steel; Pressure rise in (b) corresponds to deflection-dominated indirect loads, absent in other cases

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Fig. 10

Numerical simulation of external flow field at different time points: (a) to (c) show the reflected wave fronts moving upstream; (d) to (g) show the evolution of expansion waves

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Fig. 11

Comparison of external deformation of the cylinder (strain at M1) and fluid pressure in M2 in 2 mm polycarbonate system: (a) Schematic; (b) Concurrent pressure rise in the fluid and strain indicating indirect load

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Fig. 12

Wave propagation in the cylindrical shell and the fluid at different time points with respect to the external shock front: (a) 2 mm polycarbonate cylinder (b) 2 mm steel cylinder

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Fig. 13

Comparison of fluid pressures and external deformation (strain at M1) of the 2 mm polycarbonate cylinder (a) 25 mm radius cylinder (b) 75 mm radius cylinder




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