Stress Wave and Damage Propagation in Transparent 

Laminates at Elevated Temperatures 

by Elmar Straßburger 

ARL-CR-639 March 2010 

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Army Research Laboratory 

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ARL-CR-639 March 2010 

Stress Wave and Damage Propagation in Transparent 

Laminates at Elevated Temperatures 

Elmar Straßburger 

Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. 

prepared by 

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Stress Wave and Damage Propagation in Transparent Laminates at Elevated 

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14. ABSTRACT 

A series of studies has been conducted to visualize damage initiation and propagation in transparent armor materials like 

Starphire (a registered trademark of PPG Industries, Pittsburgh, PA) soda-lime glass, borosilicate glass, fused silica, and the

transparent ceramic AlON. Since transparent armor consists of glass laminates with polymer interlayer and backing, the 

influence of interlayer type and thickness on damage propagation was also examined. 

The so-called Edge-on Impact method was applied to visualize stress wave and damage propagation in the previous sets of 

tests. Two different optical configurations were employed. A regular transmitted light shadowgraph setup was used to observe 

wave and damage propagation, and a modified configuration, where the specimens were placed between crossed polarizers, and 

the photoelastic effect was utilized to visualize the stress waves. Pairs of impact tests at approximately equivalent velocities 

were carried out in transmitted plane (shadowgraphs) and crossed polarized light. 

The focus of this study was on the investigation of the influence of a layer of strengthened glass or glass ceramic in a laminate 

target and the influence of elevated temperatures on wave and damage propagation. 

15. SUBJECT TERMS

edge-on impact, visualization, stress waves, laminates 

16. SECURITY CLASSIFICATION OF: 

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Parimel Patel 

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iii 

Contents 

List of Figures iv

List of Tables vii

Acknowledgments viii

1. Introduction 1

2. Experimental 2

3. Complementary Baseline Results 4

3.1 Borofloat ..........................................................................................................................4

3.2 Starphire ..........................................................................................................................6

3.3 Glass Ceramics ................................................................................................................6

4. Baseline Tests With Air Gap 8

5. Laminated Targets With Strengthened Interlayer 13

6. Two-Layer Laminates at Elevated Temperature 19

7. Conclusions 25

Appendix. High-Speed Photographs 27

Distribution List 43 
iv 

List of Figures 

Figure 1. Schematic of EOI test setup. ...........................................................................................2

Figure 2. (a) Schematic of cylindrical steel projectile (cross section) and (b) photograph of 

spherical steel projectile with sabot. ..........................................................................................3

Figure 3. Schematic of the modified optical configuration. ...........................................................3

Figure 4. Selection of eight high-speed photographs from baseline test with Borofloat, 

cylindrical projectile, impact velocity 392 m/s, test no. 16591. ................................................4

Figure 5. Selection of eight high-speed photographs from baseline test with Borofloat, 

spherical projectile, impact velocity 435 m/s, test no. 16594. ...................................................5

Figure 6. Damage evolution in Borofloat after impact of cylindrical and spherical projectile 

at 400 m/s. ...............................................................................................................................5

Figure 7. Selection of eight high-speed photographs from baseline test with Starphire, 

spherical projectile, impact velocity 432 m/s, test no. 16595. ...................................................6

Figure 8. Damage evolution in Starphire after impact of cylindrical and spherical projectile 

at 400 m/s. ................................................................................................................................7

Figure 9. Selection of eight high-speed photographs from baseline test with Corning glass 

ceramic, cylindrical projectile, impact velocity 388 m/s, test no. 16592. ..................................7

Figure 10. Selection of eight high-speed photographs from baseline test with Schott glass 

ceramic, cylindrical projectile, impact velocity 393 m/s, test no. 16593. ..................................8

Figure 11. Damage evolution in glass ceramics after impact of a cylindrical projectile at 

400 m/s. ....................................................................................................................................9

Figure 12. Selection of eight high-speed photographs from test with the 100- × 50-mm 

Starphire specimen, cylindrical projectile, impact velocity 388 m/s, test no. 16580. ...............9

Figure 13. Path-time history of glass particles at the rear side of the 100- × 50-mm Starphire 

specimen, test no. 15680. .........................................................................................................10

Figure 14. Photograph of target setup (left) and shadowgraph of target (right) before impact, 

test no. 16589. ..........................................................................................................................11

Figure 15. Selection of eight high-speed photographs from test with 1.3-mm air gap between 

two 100- × 50-mm Starphire glass plates, cylindrical projectile, impact velocity 392 m/s, 

crossed polarizers, test no. 16589. ...........................................................................................11

Figure 16. Path-time history of wave and damage propagation in two-layer Starphire target 

with 1.3-mm air gap, test no. 15689. .......................................................................................12

Figure 17. Selection of eight high-speed photographs from test with very small air gap 

between two 100- × 50-mm Starphire glass plates, cylindrical projectile, impact velocity 

387 m/s, crossed polarizers, test no. 16581. ............................................................................12

Figure 18. Schematic and photograph of target with strengthened interlayer. .............................13
v 

Figure 19. Selection of eight high-speed photographs from tests with strengthened Ion 

Armor interlayer (top) and unstrengthened Ion Armor interlayer (bottom). ...........................14

Figure 20. Damage evolution in intermediate Ion Armor glass layers (strengthened and 

unstrengthened). .......................................................................................................................15

Figure 21. Damage evolution in second Starphire glass plate with intermediate Ion Armor 

glass layers (strengthened and unstrengthened). ......................................................................16

Figure 22. Selection of eight high-speed photographs from tests with glass ceramic 

interlayer. .................................................................................................................................17

Figure 23. Damage evolution in intermediate glass and glass ceramic layers. .............................18

Figure 24. Damage evolution in second Starphire glass plate with intermediate glass and 

glass ceramic layers. ................................................................................................................18

Figure 25. Overall damage evolution in targets with intermediate glass and glass ceramic 

layers. .......................................................................................................................................19

Figure 26. Specimen with temperature sensors aligned in front of the gun muzzle. ....................20

Figure 27. Specimen in target chamber with heating box. ...........................................................20

Figure 28. Pt100 temperature sensors. ..........................................................................................21

Figure 29. Temperature characteristics of Starphire specimen. ....................................................21

Figure 30. Schematic and photograph of specimen with Pt100 temperature sensors. ..................22

Figure 31. Comparison of temperature characteristics of Starphire specimen with 

temperature sensors at the surface and embedded in the bonding layer. .................................23

Figure 32. Selection of eight high-speed photographs from test with two-layer Starphire 

specimen at elevated temperature, impact velocity 389 m/s, test no. 16588. ..........................24

Figure 33. Selection of eight high-speed photographs from test with crossed polarizers 

configuration, two-layer Starphire specimen at elevated temperature, vP = 398 m/s, test 

no. 16590..................................................................................................................................24

Figure 34. Damage evolution curves from tests with two-layer Starphire laminates at 

elevated and room temperatures. .............................................................................................25 

Figure A-1. Complete set of high-speed photographs from baseline test with Borofloat, 

cylindrical projectile, impact velocity 392 m/s, test no. 16591. ..............................................28

Figure A-2. Complete set of high-speed photographs from baseline test with Borofloat, 

spherical projectile, impact velocity 435 m/s, test no. 16594. .................................................29

Figure A-3. Complete set of high-speed photographs from baseline test with Starphire, 

spherical projectile, impact velocity 432 m/s, test no. 16595. .................................................30

Figure A-4. Complete set of high-speed photographs from baseline test with Corning glass 

ceramic, cylindrical projectile, impact velocity 388 m/s, test no. 16592. ................................31

Figure A-5. Complete set of high-speed photographs from baseline test with Schott glass 

ceramic, cylindrical projectile, impact velocity 393 m/s, test no. 16593. ................................32

Figure A-6. Complete set of high-speed photographs from test with the 100- × 50-mm 

Starphire specimen, cylindrical projectile, impact velocity 388 m/s, test no. 16580. .............33
vi 

Figure A-7. Complete set of high-speed photographs from test with 1.3-mm air gap between 

two 100- × 50-mm Starphire glass plates, cylindrical projectile, impact velocity 392 m/s, 

crossed polarizers, test no. 16589. ...........................................................................................34

Figure A-8. Complete set of high-speed photographs from test with very small air gap 

between two 100- × 50-mm Starphire glass plates, cylindrical projectile, impact velocity 

387 m/s, test no. 16581. ...........................................................................................................35

Figure A-9. Complete set of high-speed photographs from test with strengthened Ion Armor 

interlayer, cylindrical projectile, impact velocity 390 m/s, test no. 16582. .............................36

Figure A-10. Complete set of high-speed photographs from test with unstrengthened Ion 

Armor interlayer, cylindrical projectile, impact velocity 384 m/s, test no. 16583. .................37

Figure A-11. Complete set of high-speed photographs from test with Corning glass ceramic 

interlayer, cylindrical projectile, impact velocity 389 m/s, test no. 16584. .............................38

Figure A-12. Complete set of high-speed photographs from test with Corning glass ceramic 

interlayer, crossed polarizers, cylindrical projectile, impact velocity 385 m/s, test no. 

16585........................................................................................................................................39

Figure A-13. Complete set of high-speed photographs from test with Schott glass ceramic 

interlayer, cylindrical projectile, impact velocity 391 m/s, test no. 16587. .............................40

Figure A-14. Complete set of high-speed photographs from test with two-layer Starphire 

laminate at ≈60 °C, cylindrical projectile, impact velocity 389 m/s, test no. 16588. ..............41

Figure A-15. Complete set of high-speed photographs from test with two-layer Starphire 

laminate at ≈60 °C, crossed polarizers, cylindrical projectile, impact velocity 398 m/s, 

test no. 16590. ..........................................................................................................................42
vii 

List of Tables 

Table 1. Test matrix for samples with strengthened interlayer. ....................................................14

Table 2. Test parameters from EOI-tests at elevated temperatures. .............................................24
viii 

Acknowledgments 

The research reported in this document has been made possible through the support and 

sponsorship of the U.S. Government through its European Research Office of the U.S. Army. 
1 

1. Introduction 

A series of studies has been conducted to visualize damage initiation and propagation in 

transparent armor materials like Starphire

 soda-lime glass, borosilicate glass, fused silica, and 

the transparent ceramic AlON.1 Since transparent armor consists of glass laminates with 

polymer interlayer and backing, the influence of interlayer type and thickness on damage 

propagation was also examined.2

 Thick glass-polymer laminates used as transparent armor in 

vehicles can heat up through intensive sunlight, which can significantly influence the 

performance of the armor. Therefore, the influence of elevated temperatures on the stress wave 

and damage propagation in a transparent laminate was examined in this study. 

The so-called Edge-on Impact (EOI) method was applied in order to visualize stress wave and 

damage propagation in the previous sets of tests. Two different optical configurations were 

employed. A regular transmitted light shadowgraph setup was used to observe wave and damage 

propagation and a modified configuration, where the specimens were placed between crossed 

polarizers, and the photoelastic effect was utilized to visualize the stress waves. Pairs of impact 

tests at approximately equivalent velocities were carried out in transmitted plane (shadowgraphs) 

and crossed polarized light. 

The objectives of the present study are as follows: 

• To determine the influence of elevated temperatures on stress wave and damage 

propagation in glass laminates. 

• To analyze the development of the damaged areas quantitatively, including previous sets of 

tests. 

• To complement the test series with glass laminates that include a layer of strengthened 

glass. 

The results of the analyses from previous tests with Starphire laminates with respect to the 

damaged areas have been presented in the 1st Interim Report.3

 This final report comprises the 

following: 

 



Starphire is a registered trademark of PPG Industries, Pittsburgh, PA.

1

Straßburger, E. High-Speed Photographic Study of Wave Propagation and Impact Damage in Transparent Aluminum 

Oxynitride (AlON); Final Report, contract no. N62558-04-P-6031, E 08/06; Ernst-Mach Institute: Efringen-Kirchen, Germany, 

February 2006. 

2Straßburger, E. High-Speed Photographic Study of Wave Propagation and Impact Damage in Transparent Laminates; Final 

Report, contract no. N62558-05-P-0303, E 12/07; Ernst-Mach Institute: Efringen-Kirchen, Germany, February 2007. 

3

Straßburger, E. Stress Wave and Damage Propagation in Transparent Laminates at Elevated Temperatures; 1st Interim 

Report, contract no. W911NF-08-1-0006, E 22/08; Ernst-Mach Institute: Efringen-Kirchen, Germany, May 2008. 
2 

• Damaged area analyses from complementary baseline tests with Borofloat, Starphire, two 

types of glass ceramic, and baseline data with an air gap between two layers of Starphire 

glass (section 3). 

• Results from laminates that include an interlayer of strengthened glass or glass ceramic 

(section 4). 

• Results from two-layer Starphire samples at elevated temperatures (section 5). 

2. Experimental 

The materials were tested in an EOI configuration, shown schematically in figure 1. 

Figure 1. Schematic of EOI test setup. 

Two types of projectiles were utilized for baseline tests to determine crack velocities, damage 

velocities, and wave propagation velocities in transparent materials—right-circular steel 

cylinders of 30-mm diameter and 53-g mass and steel spheres of 15.87-mm diameter and 16.2-g 

mass. With the steel cylinders, the nominal impact velocity was kept constant at about 400 m/s. 

A polycarbonate sabot was used to launch the steel spheres. Since the total mass of the sabot and 

 

Borofloat is a registered trademark of Schott Corporation. 
3 

steel sphere was less than the mass of the steel cylinder, the impact velocity was slightly higher 

and ranged from 420 to 440 m/s. Figure 2 shows a schematic of the steel cylinders and 

photograph of a spherical projectile with sabot. The fracture pattern generated by the spherical, 

diverging stress waves allows a measurement of the terminal crack velocity with good accuracy, 

whereas the damage pattern generated by the impact of the cylindrical projectile allows the 

measurement of damage velocities, determined by the nucleation of crack centers. 

Figure 2. (a) Schematic of cylindrical steel projectile (cross section) and 

(b) photograph of spherical steel projectile with sabot. 

For the simultaneous observation of the specimens from the side and top, an optical setup with 

two Cranz-Schardin cameras was utilized in all tests. Figure 3 shows a schematic of this optical 

configuration. 

Figure 3. Schematic of the modified optical configuration. 

 2a: 2b: 
4 

3. Complementary Baseline Results 

Complementary tests with Borofloat and Starphire glass were conducted, with extended time 

intervals of observation compared to previous tests to attain complete damage evolution curves 

for these materials. Especially with the spherical impactor, the damage evolution had only been 

observed up to about 40% of the damaged area in earlier experiments. Additionally, baseline 

damage evolution data of two glass ceramics were determined since these materials were also 

used as interlayer in laminated targets. 

3.1 Borofloat 

Two baseline tests were conducted with Borofloat glass, one with the cylindrical and one with 

the spherical projectile. Figures 4 and 5 each show a selection of eight high-speed photographs 

from these tests. The complete sets of high-speed photographs are shown in figures A-1 and A-2 

of the appendix. 

The corresponding damage evolution curves, which show the percentage of damaged area as a 

function of time, are depicted in figure 6. The data are shown, along with the results from 

previous base line tests, with a shorter time interval of observation. 

Figure 4. Selection of eight high-speed photographs from baseline test with Borofloat, cylindrical projectile, 

impact velocity 392 m/s, test no. 16591. 
5 

Figure 5. Selection of eight high-speed photographs from baseline test with Borofloat, spherical projectile, 

impact velocity 435 m/s, test no. 16594. 

Figure 6. Damage evolution in Borofloat after impact of cylindrical and spherical projectile at 

400 m/s. 

The damage evolution curves in figure 6 show agreement between the actual baseline data and 

previous sets of data. Due to the formation of crack centers ahead of the coherent fracture, front 

damage propagates much faster under impact of the cylindrical projectile. In the test with the 

cylindrical projectile, the complete area of the Borofloat sample was damaged after 28 μs, 

whereas with the spherical projectile, 90% of damaged area was reached after 55 μs.

0

20

40

60

80

100

0 10 20 30 40 50 60

Time [μs]

Damaged area [%]

# 16591, cylinder

# 15270, cylinder

# 16594, sphere

# 15291, sphere
6 

3.2 Starphire 

One complementary test with a spherical projectile and extended time intervals was conducted 

with a Starphire specimen. Figure 7 shows a selection of eight high-speed photographs from this 

test. The complete set of high-speed photographs is shown in figure A-3 of the appendix. 

Figure 7. Selection of eight high-speed photographs from baseline test with Starphire, spherical projectile, 

impact velocity 432 m/s, test no. 16595. 

It can be recognized from the selected high-speed photographs that Starphire damage evolution 

progresses slower compared to Borofloat. The quantitative analysis of the percent of damaged 

area yielded 62% after 55 μs with the Starphire, whereas 88% of damaged area was observed 

with the Borofloat specimen at the same time after impact. The damage evolution curve derived 

from the test with Starphire and the spherical projectile is plotted in figure 8, along with data 

from previous tests with spherical and cylindrical projectiles. 

3.3 Glass Ceramics 

Two types of glass ceramics were used as interlayer in laminate targets (see section 5). To 

obtain baseline data of damage evolution in these materials, one EOI test in a shadowgraph 

configuration was conducted with a cylindrical projectile for each material. The glass ceramics 

were from Schott and Corning. Figures 9 and 10 show a selection of eight high-speed 

photographs from the two tests. The complete sets of high-speed photographs are shown in 

figures A-4 and A-5 of the appendix. 
7 

Figure 8. Damage evolution in Starphire after impact of cylindrical and spherical projectile at 400 m/s. 

Figure 9. Selection of eight high-speed photographs from baseline test with Corning glass ceramic, cylindrical 

projectile, impact velocity 388 m/s, test no. 16592. 

0

20

40

60

80

100

0 10 20 30 40 50 60

Time [μs]

Damaged area [%]

# 16063, cylinder

# 16064, cylinder

# 15293, sphere

# 16595, sphere
8 

Figure 10. Selection of eight high-speed photographs from baseline test with Schott glass ceramic, cylindrical 

projectile, impact velocity 393 m/s, test no. 16593. 

With both materials, a consistently growing coherent fracture front formed by a high number of 

uniformly distributed crack centers can be recognized. The Schott glass ceramic exhibits a 

slightly rougher fracture front, which seems to be due to a slightly lower density of crack centers. 

The corresponding damage evolution curves are depicted in figure 11, along with data of 

Transarm glass ceramic from a previous set of tests.4 With all three glass ceramics examined, 

the data in figure 11 demonstrate a very similar progression of the damage evolution. 

4. Baseline Tests With Air Gap 

Most of the two-layer laminate targets tested consisted of two 100- × 50-mm glass parts, which 

were joined together by polyurethane bonding layers of different types and thicknesses. The 

influence of the bonding layer on the transmission of stress waves from one glass layer to 

another was studied comprehensively.2

 The objective of the tests with an air gap between the 

glass layers was to study the effect of damage formation through particle impact on the second 

glass layer compared to damage initiation by stress wave transmission. 

To measure the velocity of the glass fragments at the back of the first glass layer, one test was 

conducted with only one 100- × 50- × 9.4-mm specimen, which was impacted with a cylindrical 

projectile at 388 m/s. A selection of eight high-speed shadowgraphs is presented in figure 12. 

The complete set of high-speed photographs is shown in figure A-6 of the appendix. 

 4Straßburger, E. Visualization of Wave and Damage Propagation in Transparent Armor Materials—Edge-On Impact Tests 

and Analysis; Final Report, contract no. N62558-07-P-0331; E 13/08; Ernst-Mach Institute: Efringen-Kirchen, Germany, March 

2008. 
9 

Figure 11. Damage evolution in glass ceramics after impact of a cylindrical projectile at 

400 m/s. 

Figure 12. Selection of eight high-speed photographs from test with the 100- × 50-mm Starphire specimen, 

cylindrical projectile, impact velocity 388 m/s, test no. 16580. 

The photographs in figure 12 demonstrate that the glass was already damaged at the rear side of 

the specimen about 13 μs after impact and a seeming deformation of the specimen had started 

after about 15 μs. The change of the specimen’s contour at the rear side indicates that the glass 

is fragmented and particles are already moving at a high velocity. The path-time history of glass 

particles close to the center of the rear side of the specimen was determined from the 

0

20

40

60

80

100

0 5 10 15 20 25

Time [μs]

Damged area [%]

Corning, # 16592

SCHOTT, # 16593

TRANSARM, # 15908
10 

shadowgraphs. The position of the particles is plotted vs. time in figure 13. Linear regression of 

the data yielded an average velocity of 337 m/s. 

Figure 13. Path-time history of glass particles at the rear side of the 100- × 50-mm Starphire 

specimen, test no. 15680. 

With an air gap of 1.3 mm and a particle velocity of 340 m/s, the impact of the glass particles 

on the edge of the second glass layer could be expected about 3.7 μs after particles separated 

from the rear edge of the first glass plate. 

In test no. 16589 (1.3-mm air gap, crossed polarizers configuration), the first stress wave front 

was observed in the second glass plate, with a delay of about 3 μs compared to undisturbed wave 

propagation in a monolithic target. Figure 14 shows a photograph of the target setup (left) and a 

shadowgraph of the target before the impact test. A selection of eight high-speed photographs in 

crossed polarizers arrangement is presented in figure 15. The complete set of high-speed 

photographs is shown in figure A-7 of the appendix. The corresponding path-time histories of 

wave propagation and fracture propagation in the second glass plate are plotted in figure 16.

y = 0,337x + 46,99

40

50

60

70

80

0 20 40 60 80 100

Time [μs]

Position glass particles [mm]
11 

Figure 14. Photograph of target setup (left) and shadowgraph of target (right) before impact, test no. 16589. 

Figure 15. Selection of eight high-speed photographs from test with 1.3-mm air gap between two 100- 

× 50-mm Starphire glass plates, cylindrical projectile, impact velocity 392 m/s, crossed 

polarizers, test no. 16589. 
12 

Figure 16. Path-time history of wave and damage propagation in two-layer Starphire target 

with 1.3-mm air gap, test no. 15689. 

It can be recognized from the photographs in figure 15 that at about 12 μs, a stress wave has 

been initiated in the middle of the front edge of the second glass plate. The evolution of this 

wave, followed by a damage front and crack centers, can be observed in figure 17. 

Another test with a nominal air gap width of 1.3 mm was conducted in a shadowgraph 

arrangement. Due to inaccurate setup of the specimen, the width of the air gap was significantly 

smaller. This can be recognized from the selection of eight high-speed photographs in figure 17, 

where the two glass plates are hardly distinguishable. The complete set of high-speed 

photographs is presented in figure A-8 of the appendix. 

Figure 17. Selection of eight high-speed photographs from test with very small air gap between 

two 100- × 50-mm Starphire glass plates, cylindrical projectile, impact velocity 

387 m/s, crossed polarizers, test no. 16581.

0

20

40

60

80

100

0 5 10 15 20 25 30

Time [μs]

Position [mm]

t  3.0 μs

5732 m/s

5734 m/s

981 m/s (fracture)

5490 m/s
13 

5. Laminated Targets With Strengthened Interlayer 

In a previous series of tests,4 the influence of a layer of chemically strengthened glass on top of a 

Starphire specimen on damage formation was examined. A comparison of the photographs from 

the test with a front layer of strengthened glass to those with the unstrengthened front layer 

revealed no significant differences in the evolution of damage in the case of a cylindrical 

projectile. The fact that crack formation also occurred in the strengthened layer very shortly 

after impact could be explained with the high-impact stress levels, which probably exceeded the 

compressive stresses introduced by the strengthening process. 

Therefore, it was decided to examine the effect of a strengthened intermediate layer in a new 

series of EOI tests. In this case, the stress waves are already attenuated by the first glass layer 

until they arrive at the strengthened layer. The dimensions of the strengthened interlayer were 

the same as in the previous set of tests—7.65 × 9.5 × 100 mm. The total dimensions of the 

specimens were 100 × 100 × 9.5 mm, and the thickness of the bonding layers was 1.27 mm 

(50 mil). Figure 18 shows a schematic and photograph of a typical specimen. Three types of 

interlayer were studied: (1) Ion Armor

 chemically strengthened glass and unstrengthened glass 

of the same type as the reference, (2) Corning glass ceramic, and (3) a glass ceramic 

manufactured by Schott. The test parameters are listed in table 1. 

Figure 18. Schematic and photograph of target with strengthened interlayer. 

 

Ion Armor is a registered trademark of Saxon Glass Technologies, Alfred, NY. 
14 

Table 1. Test matrix for samples with strengthened interlayer. 

Test No. Interlayer VP

(m/s) 

Optical Setup Time Settings (All Tests) 

16582 Ion Armor, strengthened 390 Shadowgraph 2 4 6 8 

16583 Ion Armor, unstrengthened 384 Shadowgraph 9 10 11 12 

16584 Corning glass ceramic 389 Shadowgraph 13 14 15 16 

16585 Corning glass ceramic 385 Crossed polarizers 18 20 22 24 

16587 Schott glass ceramics 391 Shadowgraph 28 32 36 40 

A comparison of the damage evolution in targets with strengthened and unstrengthened Ion 

Armor interlayer is presented in figure 19, which shows eight high-speed photographs for each 

test. The complete sets of high-speed photographs are shown in figures A-9 and A-10 of the 

appendix. 

Figure 19. Selection of eight high-speed photographs from tests with strengthened Ion 

Armor interlayer (top) and unstrengthened Ion Armor interlayer (bottom). 

The high-speed photographs in figure 19 reveal that damage evolution in the strengthened 

interlayer is significantly slower compared to the unstrengthened interlayer. This is confirmed 

by the quantitative analysis of the fraction of damaged area. The damage evolution curves for 

the intermediate glass layers are depicted in figure 20. The unstrengthened glass layer 

Strengthened Ion Armor interlayer, test no. 16582 

Unstrengthened Ion Armor interlayer, test no. 16583 
15 

was completely damaged (no light transmission), whereas, after 25 μs, the strengthened Ion 

Armor exhibited 83% of damaged area at the end of the observation time interval (41 μs). 

Figure 20. Damage evolution in intermediate Ion Armor glass layers (strengthened 

and unstrengthened). 

Damage in the second Starphire glass plate was mainly generated after the reflection of the stress 

waves at the rear edge of the specimens. In test no. 15682 (strengthened interlayer), crack 

propagation from the center of the front edge of the second Starphire plate could also be 

observed. However, the contribution to the total damage was small, and the overall damaged 

area observed in the second Starphire plate was bigger in the case of the unstrengthened 

interlayer. This is illustrated in figure 21, which shows the damage evolution curves for the 

second Starphire glass plate.

0

20

40

60

80

100

0 10 20 30 40 50

Time [μs]

Damaged area [%]

Strengthened Ion Armor

Unstrengthened Ion Armor
16 

Figure 21. Damage evolution in second Starphire glass plate with intermediate Ion 

Armor glass layers (strengthened and unstrengthened). 

Two tests were conducted with an interlayer of the Corning glass ceramic, one test with the 

shadowgraph and another test with the crossed polarizers optical setup. The specimen with the 

Schott glass ceramics interlayer was tested using the shadowgraph configuration. Since the glass 

ceramic was not polished, it appeared black in the shadowgraphs. A selection of eight highspeed photographs is presented in figure 22. Complete sets of high-speed photographs are 

presented in figures A-11–A-13 of the appendix. 

With the Corning glass ceramic interlayer, damage behavior was observed similar to that in the 

specimen with the unstrengthened Ion Armor glass interlayer. In contrast, the specimen with the 

Schott glass ceramic interlayer exhibited a damage-reducing effect similar to the specimen with 

the strengthened Ion Armor interlayer. The results of the damaged area analysis are presented in 

figures 23 and 24, which show a comparison of the damage evolution curves in the interlayer and 

the second Starphire glass plate for the different interlayer materials. 

0

20

40

60

80

100

0 10 20 30 40 50

Time [μs]

Damaged area [%]

Strengthened Ion Armor

Unstrengthened ion Armor
17 

Figure 22. Selection of eight high-speed photographs from tests with glass ceramic interlayer. 

 Corning glass ceramic, tests no. 16584 (shadowgraph), 16585 (cr. polarizers) 

 SCHOTT glass ceramic, test no. 16587 
18 

Figure 23. Damage evolution in intermediate glass and glass 

ceramic layers. 

Figure 24. Damage evolution in second Starphire glass plate with 

intermediate glass and glass ceramic layers. 

0

20

40

60

80

100

0 10 20 30 40 50

Time [μs]

Damaged area [%]

Strengthened Ion Armor

Unstrengthened Ion Armor

Corning glass ceramic

0

20

40

60

80

100

0 10 20 30 40 50

Time [μs]

Damaged area [%]

Corning interlayer

SCHOTT interlayer

Strengthened Ion Armor

Unstrengthened Ion Armor
19 

A comparison of the overall damage development in the specimens with different glass and glass 

ceramic interlayers is presented in figure 25. Note that the damage evolution curve with the 

Schott glass ceramic interlayer only consists of the contributions of the two Starphire glass plates 

since the interlayer was not polished and therefore not transparent. However, the area of the 

interlayer covers about 7.5% of the total area of the specimen. Thus, the total damaged area 

fraction can be estimated for the phase of damage evolution in the second Starphire plate by 

adding about 4%–7% to the displayed values. 

Figure 25. Overall damage evolution in targets with intermediate glass and glass ceramic layers. 

6. Two-Layer Laminates at Elevated Temperature 

One pair of tests was conducted with a two-layer Starphire laminate with a 1.27-mm-thick 

(50-mil) bonding layer in a shadowgraph and crossed polarizers optical arrangement. The tests 

were performed at a specimen temperature of 60 °C. To heat up the specimens, a heating box 

with two copper chambers on the sides and an open bottom was used. The copper chambers 

were heated up by a flow of 90 °C hot water. The test procedure was as follows: 

0

20

40

60

80

100

0 10 20 30 40 50

Time [μs]

Damaged area [%]

Strengthened Ion Armor

Unstrengthened Ion Armor

Corning glass ceramic

SCHOTT glass ceramic

Starphire baseline
20 

1. The specimen was aligned in the target box, in front of the gun muzzle. 

2. The heating box was put over the specimen, and the specimen was heated up slowly to a 

temperature above the test temperature. 

3. The heating box was removed from the specimen. 

4. The impact test was conducted within 2 min after the removal of the heating box to avoid a 

too-high drop of the specimen temperature. 

Figure 26 shows a photograph of an aligned specimen in the target box. Figure 27 illustrates the 

specimen with the heating box. 

Figure 26. Specimen with temperature sensors aligned 

in front of the gun muzzle. 

Figure 27. Specimen in target chamber with heating 

box. 
21 

The temperature of the specimens was measured by platinum resistance temperature sensors. 

Two Pt100 platinum chip temperature sensors were glued to the surface of the specimens. 

Figure 28 shows a photograph of two sensors and their dimensions and a schematic of the sensor 

construction. 

A typical temperature curve after the removal of the heating box is presented in figure 29. The 

positions of the temperature sensors can be seen from figure 26. 

Figure 28. Pt100 temperature sensors. 

Figure 29. Temperature characteristics of Starphire specimen. 

The curves in figure 29 show that the maximum (starting) temperature was higher at the upper 

edge of the specimen. This is due to the fact that the heating box is open at the bottom, whereas 

the upper part of the specimen is completely surrounded by the heating box. However, the 

20

30

40

50

60

70

80

0 2 4 6 8 10 12

Time/ minutes

Temperature/ °C

T-sensor top, surface

T-sensor bottom, surface
22 

temperature drops faster at the upper edge of the specimen when the heating box is removed. 

The difference between the two curves can be explained by the fact that the lower edge of the 

specimen is glued to the polycarbonate target mount, which has also been heated up and 

therefore slows down the temperature drop in the lower part of the specimen during the first 

minutes. About 1 1/2 min after removal of the heating box, the temperature was nearly equal at 

both sensor positions. 

The EOI tests were performed with temperature sensors only at the surface of the specimens. In 

order to measure the temperature in the interior of the specimens, especially within the bonding 

layer, one specimen was instrumented with two additional Pt100 sensors embedded in the 

bonding layer. Figure 30 shows a schematic and photograph of the specimen and the sensor 

positions. This specimen was only used for a comparison of the temperature measurements at 

the surface and in the bonding layer. The results of this measurement are presented in figure 31. 

The temperatures measured within the bonding layer after slowly heating the specimen were 

higher than the temperatures at the surface. Similar to the measurements at the surface, the 

temperature dropped faster in the upper part of the specimen. However, the difference between 

the temperature gradients was not as high as with the surface sensors. The curves did not cross 

during the 10 min of the measurement. 

Figure 30. Schematic and photograph of specimen with Pt100 temperature sensors. 
23 

Figure 31. Comparison of temperature characteristics of Starphire specimen with 

temperature sensors at the surface and embedded in the bonding layer. 

The test parameters of the EOI tests at elevated temperature are listed in table 2. The time 

settings were the same as in the tests with the strengthened interlayer (see table 1). Damage and 

wave propagation at elevated temperatures is illustrated in figures 32 and 33, which show a 

selection of eight high-speed photographs from the two tests. The complete sets of high-speed 

photographs are presented in figures A-14 and A-15 of the appendix. 

The high-speed photographs in figures 32 and 33 do not reveal significant differences when 

compared to the results from tests with equal laminates at room temperatures. This qualitative 

impression is confirmed by the quantitative damaged area analysis. The damage evolution curve 

of test no. 16588 is plotted in figure 34, along with the curve from the corresponding test at room 

temperature (test no. 15299). 

The damage evolution curves from both tests are nearly identical. At elevated temperatures, a 

possible softening of the bonding layer is expected that could lead to a decrease of stiffness and, 

therefore, an increased bending of the single glass layers in a transparent armor. Compared to 

the setup used in the EOI tests, the thickness of the glass layers in an armor configuration is 

much smaller. This could explain why no effect of the elevated temperature was seen in the tests 

conducted here. The thickness and type of the bonding layer are also expected to play a role in 

the amount of the effect of elevated temperatures. 

30

40

50

60

70

80

90

0 2 4 6 8 10 12

Time/ minutes

Temperature/ °C

T-sensor top, surface

T-sensor top, embedded

T-sensor bottom, surface

T-sensor bottom, embedded
24 

Table 2. Test parameters from EOI-tests at elevated temperatures. 

Test No. VP

(m/s) 

Optical Setup 

Surface Temperature (T) 

(°C)

TMax TImpact

TSensor top TSensor bottom TSensor top TSensor bottom

16588 389 Shadowgraph 74.0 57.4 60.0 51.9 

16590 398 Crossed polarizers 75.7 63.4 63.4 59.2 

Figure 32. Selection of eight high-speed photographs from test with two-layer Starphire specimen at elevated 

temperature, impact velocity 389 m/s, test no. 16588. 

Figure 33. Selection of eight high-speed photographs from test with crossed polarizers configuration, two-layer 

Starphire specimen at elevated temperature, vP = 398 m/s, test no. 16590. 
25 

Figure 34. Damage evolution curves from tests with two-layer Starphire laminates at 

elevated and room temperatures. 

7. Conclusions 

The focus of this study was on the investigation of the influence of a layer of strengthened glass 

or glass ceramic in a laminate target and the influence of elevated temperatures on wave and 

damage propagation. 

Baseline tests with different glasses, using cylindrical and spherical projectiles and extended 

time intervals of observation, showed agreement with damage evolution in previous tests. 

In contrast to previous results with Ion Armor front layers, damage evolution was significantly 

slower when Ion Armor-strengthened glass was used as interlayer. Damage in the second 

Starphire layer was also reduced in the case of the strengthened Ion Armor interlayer. 

Two types of glass ceramic were also tested as interlayer. With a Schott glass ceramic interlayer, 

a damage-reducing effect similar to the specimen with the strengthened Ion Armor interlayer was 

observed. With the Corning glass ceramic interlayer, damage behavior was observed similar to 

that in the specimen with the unstrengthened Ion Armor glass interlayer. 

Edge-on Impact tests with two-layer Starphire laminates at temperatures of ≈60 °C did not reveal 

a different damage behavior compared to tests at room temperature. 

0

20

40

60

80

100

0 5 10 15 20 25 30 35 40 45

Time [μs]

Damaged area [%]

Test No.16588, 60°C

Test No. 15299, 20°C
26 

INTENTIONALLY LEFT BLANK. 
27 

Appendix. High-Speed Photographs 
28 

Figure A-1. Complete set of high-speed photographs from baseline test with Borofloat, cylindrical projectile, 

impact velocity 392 m/s, test no. 16591. 
29 

Figure A-2. Complete set of high-speed photographs from baseline test with Borofloat, spherical projectile, 

impact velocity 435 m/s, test no. 16594. 
30 

Figure A-3. Complete set of high-speed photographs from baseline test with Starphire, spherical projectile, 

impact velocity 432 m/s, test no. 16595. 
31 

Figure A-4. Complete set of high-speed photographs from baseline test with Corning glass ceramic, cylindrical 

projectile, impact velocity 388 m/s, test no. 16592. 
32 

Figure A-5. Complete set of high-speed photographs from baseline test with Schott glass ceramic, cylindrical 

projectile, impact velocity 393 m/s, test no. 16593. 
33 

Figure A-6. Complete set of high-speed photographs from test with the 100- × 50-mm Starphire specimen, 

cylindrical projectile, impact velocity 388 m/s, test no. 16580. 
34 

Figure A-7. Complete set of high-speed photographs from test with 1.3-mm air gap between two 100- 

× 50-mm Starphire glass plates, cylindrical projectile, impact velocity 392 m/s, crossed 

polarizers, test no. 16589. 
35 

Figure A-8. Complete set of high-speed photographs from test with very small air gap between two 100- 

× 50-mm Starphire glass plates, cylindrical projectile, impact velocity 387 m/s, test no. 16581. 
36 

Figure A-9. Complete set of high-speed photographs from test with strengthened Ion Armor interlayer, 

cylindrical projectile, impact velocity 390 m/s, test no. 16582. 
37 

Figure A-10. Complete set of high-speed photographs from test with unstrengthened Ion Armor interlayer, 

cylindrical projectile, impact velocity 384 m/s, test no. 16583. 
38 

Figure A-11. Complete set of high-speed photographs from test with Corning glass ceramic interlayer, 

cylindrical projectile, impact velocity 389 m/s, test no. 16584. 
39 

Figure A-12. Complete set of high-speed photographs from test with Corning glass ceramic interlayer, 

crossed polarizers, cylindrical projectile, impact velocity 385 m/s, test no. 16585. 
40 

Figure A-13. Complete set of high-speed photographs from test with Schott glass ceramic interlayer, cylindrical 

projectile, impact velocity 391 m/s, test no. 16587. 
41 

Figure A-14. Complete set of high-speed photographs from test with two-layer Starphire laminate at ≈60 °C, 

cylindrical projectile, impact velocity 389 m/s, test no. 16588. 
42 

Figure A-15. Complete set of high-speed photographs from test with two-layer Starphire laminate at 

≈60 °C, crossed polarizers, cylindrical projectile, impact velocity 398 m/s, test no. 16590. 
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