Damage Assessment of a Small Spherical Projectile 

Impacting on a Glass Shield 

by Jian H. Yu, Peter G. Dehmer, and James M. Sands 

ARL-MR-711 January 2009 

Approved for public release; distribution is unlimited. 
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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-MR-711 January 2009 

Damage Assessment of a Small Spherical Projectile 

Impacting on a Glass Shield 

Jian H. Yu, Peter G. Dehmer, and James M. Sands 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
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1. REPORT DATE (DD-MM-YYYY)

January 2009 

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Final 

3. DATES COVERED (From - To) 

1 October 2008–1 November 2008 

4. TITLE AND SUBTITLE 

Damage Assessment of a Small Spherical Projectile Impacting on a Glass Shield 

5a. CONTRACT NUMBER 

5b. GRANT NUMBER 

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6. AUTHOR(S) 

Jian H. Yu, Peter G. Dehmer, and James M. Sands 

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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

U.S. Army Research Laboratory 

ATTN: AMSRD-ARL-WM-MD 

Aberdeen Proving Ground, MD 21005-5069 

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ARL-MR-711 

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13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

A high-speed photographic method was set up to track a small projectile in flight and capture its subsequent impact on a glass 

shield. A 1.0-mm-diameter steel ball bearing was launched from a compressed helium gas gun. The flight of the projectile and 

the impact event were captured with high-speed cameras. The glass shield showed visible damage at an impact speed of more 

than 205 m/s. 

15. SUBJECT TERMS

small projectile, glass shield, impact 

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OF ABSTRACT 

UL 

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10 

19a. NAME OF RESPONSIBLE PERSON

Jian H. Yu 

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410-306-0878 

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iii

Contents 

List of Figures iv

List of Tables iv

1. Materials and Methods 1

2. Results 2

Distribution List 4 
iv

List of Figures 

Figure 1. Setup diagram for small spherical projectile impact analysis. ........................................1

Figure 2. Speed determination: overlay of four frames of exposures. The horizontal 

distance between the cross hairs is 10 mm. ...............................................................................2

Figure 3. Damaged areas on targets: impact speed of 205 m/s (left) and impact speed of 

250 m/s (right). The white scale bar is 3.5 mm. .......................................................................3

List of Tables 

Table 1. Glass target impact results. ...............................................................................................2
1

1. Materials and Methods 

The projectile is a 1.0-mm-diameter steel ball bearing (E52100 alloy) that weights 4.02 mg. It 

was launched from a 0.22-cal. gas gun without a sabot. The gas gun was pressurized at different 

pressures, with helium gas to propel the projectile at different velocities. The speed of the 

projectile was not controlled precisely; however, higher pressurization generally produced a 

faster projectile speed. When the projectile passed in front of a transparent grid sheet, the 

shadow of the projectile was captured by a high-speed camera (Photron SA1). The pictures were 

taken at a resolution of 512  512 dpi, a camera speed of 200,000 frames/second, and an 

exposure time of 1/551,000 s. The path of the projectile was no more than 5 mm away from the 

transparent grid sheet (see figure 1). The camera lens (Nikon AF-Nikkor) was set at 85-mm 

focal length, with an f-stop of 22 to capture the shadow and the grid in focus. The speed of the 

projectile was determined by measuring the displacement of the shadow in 150 s using Photron 

PFV software (see figure 2). The displacement measurement was accurate to ±0.05 mm; the 

measured speed accuracy was ±10 m/s. Another high-speed camera (same settings as just 

mentioned) was used to capture the impact of the projectile on the glass target. High-intensity 

lamps were used to back light the target. The glass target (Schott Borofloat 33 glass, 101.6 

101.6  1.11 mm) was held onto a 1-in-thick Plexiglas*

 frame with 3M double-sided foam tape 

on all four edges. 

Figure 1. Setup diagram for small spherical projectile impact analysis. 

 *

Plexiglas is a trademark of Rohm & Haas Company. 
2

Figure 2. Speed determination: overlay of four frames of exposures. The 

horizontal distance between the cross hairs is 10 mm. 

2. Results 

The glass targets were impacted at different projectile speeds ranging from 107 to 250 m/s 

(see table 1). The maximum recorded speed that produced no damage on the glass target was 

186 m/s; the minimum impact speed that caused target failure was 205 m/s. The projectile did 

not penetrate through the target. Instead, the projectile ricocheted off the target on impact. All 

the damaged targets had a truncated cone fracture (see figure 3). Lateral cracking also occurred 

at the damaged area. More lateral cracks were observed at a higher speed. 

Table 1. Glass target impact results. 

Projectile Speed 

(m/s) 

Results on Glass Target 

107 No damage 

172 No damage 

186 No damage 

205 Fractured 

250 Fractured 
3

Figure 3. Damaged areas on targets: impact speed of 205 m/s (left) and impact speed of 250 m/s 

(right). The white scale bar is 3.5 mm. 
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