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Research Papers

Finite Element Modeling of Blast Lung Injury in Sheep

[+] Author and Article Information
Melissa M. Gibbons

Mem. ASME
L-3/Applied Technologies, Inc.,
Simulation, Engineering, and Testing,
10770 Wateridge Circle, Suite 200,
San Diego, CA 92121
e-mail: Melissa.Gibbons@L-3Com.com

Xinglai Dang

L-3/Applied Technologies, Inc.,
Simulation, Engineering, and Testing,
10770 Wateridge Circle, Suite 200,
San Diego, CA 92121
e-mail: Xinglai.Dang@L-3Com.com

Mark Adkins

L-3/Applied Technologies, Inc.,
Simulation, Engineering, and Testing,
10770 Wateridge Circle, Suite 200,
San Diego, CA 92121
e-mail: Mark.Adkins@L-3Com.com

Brian Powell

L-3/Applied Technologies, Inc.,
Simulation, Engineering, and Testing,
10770 Wateridge Circle, Suite 200,
San Diego, CA 92121
e-mail: Brian.Powell@L-3Com.com

Philemon Chan

L-3/Applied Technologies, Inc.,
Simulation, Engineering, and Testing,
10770 Wateridge Circle, Suite 200,
San Diego, CA 92121
e-mail: Philemon.Chan@L-3Com.com

1Corresponding author.

Manuscript received June 5, 2014; final manuscript received November 14, 2014; published online February 5, 2015. Assoc. Editor: Joel D. Stitzel.

J Biomech Eng 137(4), 041002 (Apr 01, 2015) (9 pages) Paper No: BIO-14-1251; doi: 10.1115/1.4029181 History: Received June 05, 2014; Revised November 14, 2014; Online February 05, 2015

A detailed 3D finite element model (FEM) of the sheep thorax was developed to predict heterogeneous and volumetric lung injury due to blast. A shared node mesh of the sheep thorax was constructed from a computed tomography (CT) scan of a sheep cadaver, and while most material properties were taken from literature, an elastic–plastic material model was used for the ribs based on three-point bending experiments performed on sheep rib specimens. Anesthetized sheep were blasted in an enclosure, and blast overpressure data were collected using the blast test device (BTD), while surface lung injury was quantified during necropsy. Matching blasts were simulated using the sheep thorax FEM. Surface lung injury in the FEM was matched to pathology reports by setting a threshold value of the scalar output termed the strain product (maximum value of the dot product of strain and strain-rate vectors over all simulation time) in the surface elements. Volumetric lung injury was quantified by applying the threshold value to all elements in the model lungs, and a correlation was found between predicted volumetric injury and measured postblast lung weights. All predictions are made for the left and right lungs separately. This work represents a significant step toward the prediction of localized and heterogeneous blast lung injury, as well as volumetric injury, which was not recorded during field testing for sheep.

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Figures

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Fig. 4

(a) Three-point bending experiment setup. (b) Diagram of experiment, where x = 3.5 cm and ΔL = 7 cm. The diameter of the upper impactor is 12.7 mm, and the diameters of the lower supports are 6.2 mm.

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Fig. 5

(a) Three-point bending of the seventh rib simulated in LS-DYNA. (b) Experimental force–displacement response for the seventh rib (solid line) at a displacement rate of 1 mm/s, compared to the FEM simulation results (dashed line) using the calibrated material parameters of the elastic–plastic constitutive model.

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Fig. 3

Sheep thorax FEM (left). Shell elements used to model ribcage (upper right). The solid meshes of the upper thoracic organs are highlighted (lower right).

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Fig. 2

Sample pressure histories measured by a BTD during a complex wave blast. BTD Sensor #1 is facing the blast and Sensor #3 is facing the corner of the enclosure.

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Fig. 1

BTD placement in the corner of the enclosure (a) and sensor configuration viewed from the top (b). The vertical placement of the BTD in the corner replicates the positioning of the sheep, which were hung vertically in a sling.

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Fig. 6

Four pressure traces measured by the BTD are applied to the sheep FEM skin surface. Sheep were blasted right-side-on, so pressure data from Sensor #1 is applied to the anatomical right side of the sheep FEM.

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Fig. 7

Comparison of the normalized work from INJURY 8.3 with the normalized internal energy from the FEM for each of the complex wave blast cases that were simulated. The linear fit is y = 0.6727x + 0.03321 with R2= 0.9239.

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Fig. 12

Fractional lung weight of the left (left) and right (right) lungs, normalized by the average of control animals, plotted against predicted lung volumetric injury. Fractional lung weight is lung weight divided by total body weight. The dashed line is the quadratic fit to the binned data; for the left lung y = 0.00035x2+ 0.00059x + 0.99638 with R2= 0.9871, for the right lung y = 0.00019x2+ 0.00239x + 0.99524 with R2= 0.9921.

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Fig. 8

Comparison of pathology photographs of sheep lungs (top), and maximum values of the strain product in the sheep FEM lung surface elements for the same blast (bottom). The blast level increases from left to right.

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Fig. 9

Threshold value of the strain product required to match experimentally observed lung injury results plotted against normalized FEM internal energy. Solid diamonds show results binned together by normalized work along with standard deviation bars. The dashed line is the linear fit to the binned data, with y = −1228x + 371, and R2= 0.9902.

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Fig. 10

Comparison of total observed lung injury and total predicted lung injury, when the varying strain product threshold is used to calculate predicted area. The dashed line is the linear fit to the binned data, y = 1.016x − 1.186 with R2= 0.9928.

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Fig. 11

Predicted versus observed area injured for the left and right lungs separately. The dashed line is the linear fit to the binned data; for the left lung y = 1.063x − 7.257 with R2= 0.9958, for the right lung y = 1.037x + 3.076 with R2= 0.9973.

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