Research Papers

Modeling of Advanced Combat Helmet Under Ballistic Impact

[+] Author and Article Information
Y. Q. Li

Department of Mechanical Engineering,
Southern Methodist University,
P. O. Box 750337,
Dallas, TX 75275-0337

X. G. Li

Department of Mechanical Engineering,
Southern Methodist University,
P. O. Box 750337,
Dallas, TX 75275-0337;
Division of Neuronic Engineering,
School of Technology and Health,
Royal Institute of Technology (KTH),
Huddinge 141 52, Sweden

X.-L. Gao

Fellow ASME
Department of Mechanical Engineering,
Southern Methodist University,
P. O. Box 750337,
Dallas, TX 75275-0337
e-mail: xlgao@smu.edu

1Corresponding author.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received May 9, 2015; final manuscript received July 16, 2015; published online August 12, 2015. Assoc. Editor: Weinong Chen.

J. Appl. Mech 82(11), 111004 (Aug 12, 2015) (9 pages) Paper No: JAM-15-1235; doi: 10.1115/1.4031095 History: Received May 09, 2015

The use of combat helmets has greatly reduced penetrating injuries and saved lives of many soldiers. However, behind helmet blunt trauma (BHBT) has emerged as a serious injury type experienced by soldiers in battlefields. BHBT results from nonpenetrating ballistic impacts and is often associated with helmet back face deformation (BFD). In the current study, a finite element-based computational model is developed for simulating the ballistic performance of the Advanced Combat Helmet (ACH), which is validated against the experimental data obtained at the Army Research Laboratory. Both the maximum value and time history of the BFD are considered, unlike existing studies focusing on the maximum BFD only. The simulation results show that the maximum BFD, the time history of the BFD, and the shape and size of the effective area of the helmet shell agree fairly well with the experimental findings. In addition, it is found that ballistic impacts on the helmet at different locations and in different directions result in different BFD values. The largest BFD value is obtained for a frontal impact, which is followed by that for a crown impact and then by that for a lateral impact. Also, the BFD value is seen to decrease as the oblique impact angle decreases. Furthermore, helmets of four different sizes—extra large, large, medium, and small—are simulated and compared. It is shown that at the same bullet impact velocity the small-size helmet has the largest BFD, which is followed by the medium-size helmet, then by the large-size helmet, and finally by the extra large-size helmet. Moreover, ballistic impact simulations are performed for an ACH placed on a ballistic dummy head form embedded with clay as specified in the current ACH testing standard by using the validated helmet model. It is observed that the BFD values as recorded by the clay in the head form are in good agreement with the experimental data.

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Grahic Jump Location
Fig. 2

Dimensions (left) and FE mesh (right) of an FMJ bullet. All dimensions are in mm.

Grahic Jump Location
Fig. 3

Ballistic dummy head form with a clay insert. From left to right, the geometry, FE mesh of the dummy head, FE model of the dummy head form with clay embedded, and the final assembly of the helmet on the dummy head form. The geometry is adopted from Ref. [11].

Grahic Jump Location
Fig. 1

(a) FE mesh of a large-size ACH shell and (b) FE mesh of foam pads. Here, “1” and “2” represent the two in-plane directions and “3” stands for the thickness direction.

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Fig. 4

(a) The time sequence of the impact events showing the deformation of the helmet shell and the bullet, and (b) the deformation of the helmet shell when the BFD reaches its maximum

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Fig. 5

(a) The BFD viewed from inside, (b) the time history of the BFD, and (c) the velocity profile. The experimental data plotted for comparison are obtained from Ref. [6].

Grahic Jump Location
Fig. 7

Different damage modes of the helmet shell under ballistic impact when the BFD reaches its maximum. (a) Fiber damage in the warp direction, (b) fiber damage in the fill direction, (c) fiber crush damage, (d) perpendicular matrix (in-plane shear) damage, and (e) parallel matrix (delamination) damage. Here, f1–f5 represent the damage functions for the respective damage modes defined in Ref. [29] and adopted in mat 162 of ls-dyna [26].

Grahic Jump Location
Fig. 8

Effects of impact locations and directions on the helmet BFD. The time history of the BFD for the frontal, crown, and lateral (right side) impacts (from upper to lower) is shown on the left, and the time history of the BFD for the right-side oblique impact with an impact angle of 90 deg, 60 deg, and 45 deg (from upper to lower) is displayed on the right.

Grahic Jump Location
Fig. 6

(a) The energy conversion in the system, and (b) the distribution of the internal energy in the helmet shell and bullet

Grahic Jump Location
Fig. 9

Effect of helmet size on the BFD. The experimental curve shown is obtained from Ref. [6].

Grahic Jump Location
Fig. 10

Stand-off distance for the head form/clay at the right-side lateral and crown impact locations (left) and at the frontal impact location (right), as marked by each short rectangular bar. The foam pads between the helmet shell and the dummy head/clay are not shown.

Grahic Jump Location
Fig. 11

BFD as recorded by the clay using the dummy head/clay as a fixture for (a) the frontal impact, (b) the crown impact, and (c) the right-side lateral impact



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