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The subsequent sections of this chapter will focus on areas 9.3.1. Density and Dimension Measurements
(1), (4), and (5). Specific attention will be given to the glass
Several densities of the glass foam material were examined.
foam material testing that was conducted and the calibration
The higher density samples had higher compressive strengths.
of the computer models to match the tests. The development
Preliminary screening indicated that the lowest density spec-
of the tire models (2) and aircraft model (3) will be reserved
imens, at nominally 6 pcf, were most promising for this appli-
for Appendix F and Appendix G, respectively.
cation. The remainder of the testing discussion is confined
to this density of the material. Specimens were obtained in
9.3. Testing Effort cylindrical shapes with 3.65- and 5.625-in. diameters and
larger 24 × 18 × 5-in. blocks.
The testing effort for the glass foam material involved
an extensive battery of mechanical and environmental
tests. Table 9-1 depicts the overall test matrix for the glass 9.3.2. Platen Compression Tests
foam material.
9.3.2.1. Low Rate
All cylinder dimensions specify diameter followed by height.
Conditioned specimens were environmental test specimens Platen compression tests were performed for the initial mat-
that were compression-tested following freezethaw exposure. erial density screening, enabling a rapid down-selection to the
These cylinders were only 2.5 in. tall to maintain the aspect ratio 6 pcf density as the most likely candidate. The platen compres-
of prior "short" cylinder specimens. The specimen diameter sion tests further permitted the evaluation of the energy absorp-
was constrained by the environmental test apparatus. tion capacity of the material and the effects of loading rate.
Table 9-1. Test matrix for glass foam material.
Test Properties Detail Number of Tests
Characterized
Laboratory Tests
Hydrostatic · Compressive strength at · Per ASTM D2850 0 psi 1
Triaxial failure (u) · 3.65 x 8" cylinder
5 psi 2
Compression · Shear strength (u) · 0.0592 in./min compression rate
Test · Maximum compression of 5 to 10% 10 psi 2
· Confining pressures of 0, 5, 10,
20 psi 2
and 20 psi
Total: 7
Parallel Platen · Compressive strength at · Version 1: low speed, tall Fresh
Compression failure (u) · Non-standard
Capped: 2
Test · Compressive stress · 3.65 x 8" cylinder
strain curve · 3 in./min compression rate Uncapped: 3
· Extrapolated: volumetric · Maximum compression of 85%
Conditioned
energy capacity · Unconfined flat disk specimen
· Determined for different compression Uncapped: 2
strain rates
· Version 2: low speed, short Capped: 2
· Non-standard
Uncapped: 3
· 5.625 x 4" cylinder
· 3 in./min compression rate
· Maximum compression of 85%
· Version 2: high speed, short Capped: 2
· Non-standard
Uncapped: 3
· 5.625 x 4" cylinder
· 60 in./sec compression rate
· Maximum compression of 70%
Punch · Combined compression · Non-standard 5
Compression and shear strain · 5" thick material block
Test behavior · 1.5" punch diameter
· Somewhat similar to · 3 in./min compression rate
EMAS material testing · Maximum compression of 70%
method
Environmental · Durability to freeze · Per ATSM C 666/C 666M-03 2
Chamber Tests thaw cycles (modified)
· Effectiveness of sealant · 3.65 x 2.5" cylinder
treatments, where · 78 freeze-thaw cycles
applicable
Pendulum Test
Pendulum One- · Dynamic response for · Non-standard 2
Wheel Bogey the material to a · 16.9 mph collision
Test moderate-speed tire · 24 x 18 x 5" blocks, glued into
overrun characterized stacks
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Figure 9-4. Low-rate uncapped platen test of glass foam pre-test (left) and post-test (right).
Low-rate platen tests were conducted by placing a cylindrical 9.3.2.2. High Rate
specimen between two metal platens. The upper platen was
then displaced downward at a fixed rate of 3 in. per minute High-rate compression tests (60 in.-s) were conducted on
until the specimen was fully compressed. short cylinders (5.625 × 4 in.) to evaluate the effects of rapid
The platen tests were conducted with and without Sor- compression on the material. For a B747 main-gear tire travel-
bothane capping material on the top and bottom of the spec- ling at 70 knots, the average vertical compression rate would be
imens to determine whether capping was beneficial or not. 40 in./(in.-s). The test produced an average strain rate of 150 in./
For the uncapped specimens, the material crushed in a local- (in.-s), which exceeds the overrun case by a substantial margin.
ized failure zone immediately adjacent to the platen. These When comparing the high- and low-rate loading curves,
specimens maintained their shape throughout the duration only a minimal difference is observed, which could be due only
of the loading up to the final 85% compression state, which to inertial effects of the material. Overall, the high-rate platen
aided in capturing the full energy absorption of the material
(Figure 9-4).
When caps were used, the specimens tended to split along
vertical planes, causing a shape change that often led to early
terminations of the compression test (Figure 9-5). The un-
capped approach was eventually favored due to its superior test
repeatability and its ability to capture the full energy capacity
of the material.
Tall and short cylinder specimens were tested for compar-
ison with the hydrostatic triaxial tests, which used tall cylinders
(3.65 × 8 in.), and the high-rate platen tests, which used short
cylinders (5.625 × 4 in.).
The glass foam material exhibited a characteristic crush-
able foam load history that rose to a plateau value, where
it remained until the material approached full compression
(Figure 9-6). Near full compression, the material hardened and
the loading increased. The stressstrain curve was integrated
to produce the energy absorption curve shown in the figure. Figure 9-5. Mid-test splitting of low-rate capped
No measurable rebound occurred after compression. platen test cylinder of glass foam.
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80 48 70 56
70 42 60 48
Energy Absorption [psi/in2]
Energy Absorption [psi/in3]
60 36
50 40
50 30
Stress [psi]
Stress [psi]
40 32
40 24
30 24
30 18
20 16
20 12 Stress, Average of Test Data
Energy Absorbed Per Unit Volume
10 Stress, Average of Test Data 6 10 8
Energy Absorbed Per Unit Volume
0 0 0 0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Strain [in./in.] Strain [in./in.]
Figure 9-6. Average load history for glass foam Figure 9-7. Average load history for glass foam
material from low-rate platen tests, tall specimen. material from high-rate platen tests, short
specimen.
tests indicate that there is little to no practical rate effect in the
material for the loading regimes of interest (Figure 9.7). The specimens were tall cylinders (3.65 × 8 in.) placed
between platens using Sorbothane caps at the top and bottom
(Figure 9-8, left). The specimens were fitted with flexible
9.3.2.3. Hydrostatic Triaxial Tests
membrane sleeves before immersion in a pressurized vessel of
The hydrostatic triaxial tests evaluated the glass foam per- water. While at this hydrostatic pressure, the specimens were
formance at different confining pressures to determine if any compressed axially until failure.
strength increase or bulking deformation took place. Neither As observed in the platen tests, the use of capping induced
was anticipated because the glass foam material behaved as a vertical failure plane formation in the specimen (Figure 9-8,
one-dimensional foam with little to no observed lateral bulking right), which typically occurred at a compression displacement
(low Poisson ratio). of about 5%. This failure load did show a mild dependence on
Sorbothane Cap
Figure 9-8. Hydrostatic triaxial compression test of glass foam pre-test (left) and post-test (right).
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Figure 9-9. Punch test of glass foam test specimen pre-test (left) and post-test (right).
confinement pressure, though no bulking behaviors were similar to the characterization tests performed by the current
observed. EMAS manufacturer (34). However, the tests differed with
regard to the proportional aspect ratio of the punch, the punch
shape, the specimen size, and the loading rate.
9.3.3. Punch Tests
The resulting load was due to a combination of the com-
Punch tests were performed by pressing a 1.5-in. diameter, pression strength of the material (area under the punch) and
smooth-sided punch into a 5-in. thick block of the material the shear strength of the material (circumferential edge of the
(Figure 9-9). The glass foam material compressed cleanly, punch). Figure 9-10 illustrates the averaged load history for
leaving a smooth-sided hole in the block. These tests were the punch tests. As shown, the effective "pressure" on the
200 100
180 90
160 80
140 70
Energy Absorption (psi/in3)
120 60
Pressure (psi)
100 50
80 40
60 30
40 20
Compression Force Average
20 Energy Absorption 10
0 0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Strain (in./in.)
Figure 9-10. Average load history for glass foam material from
punch test with stress normalized for cross-sectional area of
1.5-in. diameter punch.
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punch was nominally 140 psi, which compares at 2.5 times
the nominal 55 psi strength of the material exhibited in the
platen tests (Figure 9-6). This increase in apparent strength
is due to confinement and shear contributions. In arrestor
applications, the shear strength of the material would be rele-
vant along the vertical walls of the tire rut.
9.3.4. Pendulum Tests
9.3.4.1. Pendulum Apparatus
In addition to the small-scale laboratory tests, a larger-scale
one-wheel bogy test was conducted using a large pendulum
test apparatus. The pendulum test apparatus featured a heavy
4,400-lb mass that hung from an overhead support frame,
giving it a swing arc of 24.5 ft. The mass was hoisted to the
desired height and then released; the speed of the mass was
controlled by the release height.
The pendulum mass was fitted with a strut and wheel
assembly, which Figure 9-11 illustrates in an exploded view. The
strut was instrumented with three load cells that measured
loads at the connections. These three connection loads were
resolved into orthogonal vertical and drag loads on the strut
and wheel assembly.
To reduce the number of variables in the design, a rigid
aluminum wheel form was used rather than a pneumatic tire.
The diameter and width were 14.8 and 5.5 in., respectively.
These proportions were based on a nominal one-third scale
B737-800 main-gear tire, which has a diameter and width of
44.5 and 16.5 in., respectively.
9.3.4.2. Glass foam retention box.
Figure 9-11. Pendulum test device with one-wheel
Below the pendulum assembly, a box was constructed to bogy.
retain larger blocks of the glass foam, which each measured
24 × 18 × 5 in. The blocks were arranged in one row, 6 blocks
long and 2 blocks in depth, for a total of 12 blocks. The over-
all dimensions were 9 ft in length, 2 ft in width, and 10 in. in Figure 9-13 shows the rut created through the material by
height. The upper and lower blocks were glued in 6 pairs, the strut and wheel of the pendulum; the wheel cut a clean
which were placed in the retention box and held in place by path through the material, leaving the RG-1 material adjacent
an upper cap rail around the perimeter. The block pairs were to the rut essentially undamaged. This behavior was consistent
not adhered to one another. Figure 9-12 shows the overall with expectations based on the small-scale testing.
pendulum apparatus with the glass foam blocks beneath it.
9.3.4.4. Landing Gear Loads
9.3.4.3. Tests Executed
The loading history for the pendulum strut showed oscil-
For the tests, the pendulum was set to swing such that the lations in both the drag and vertical loads (Figure 9-14). It is
wheel penetrated to a depth of nominally one-third diameter, believed that these pulses were caused by the seams between
or 5.0 in. One swing height was used to produce an average the block pairs in the bed. As the wheel approached the end of
overrun speed of 16.9 mph. Due to the single-use nature of a block, the load decreased; when the wheel began to overrun
the material and the limited supply of evaluation samples, the next block, the load increased. Since the blocks were not
two tests were conducted for these conditions. Both tests gave glued at the seams, these joints presented a discontinuity in
consistent results. the material. The pulsing effect was further amplified by the
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Pendulum Mass
Retention Box
with Glass Foam
Blocks
Strut and
Wheel
Assembly
Cap Rail
Figure 9-12. Overview of pendulum test setup for glass foam.
Figure 9-13. Post-test results from pendulum test for glass foam.
