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Research Papers: Gas Turbines: Ceramics

# Foreign Object Damage in an Oxide/Oxide Composite at Ambient Temperature

[+] Author and Article Information
Sung R. Choi1

Naval Air Systems Command, Patuxent River, MD 20670sung.choi1@navy.mil

Donald J. Alexander, Robert W. Kowalik

Naval Air Systems Command, Patuxent River, MD 20670

1

Corresponding author.

J. Eng. Gas Turbines Power 131(2), 021301 (Dec 24, 2008) (6 pages) doi:10.1115/1.2969091 History: Received April 09, 2008; Revised April 10, 2008; Published December 24, 2008

## Abstract

Foreign object damage behavior of an oxide/oxide (N720/AS) ceramic matrix composite was determined at ambient temperature using impact velocities ranging from 100 m/s to 400 m/s by 1.59 mm diameter steel-ball projectiles. Two different support configurations of target specimens were used: fully supported and partially supported. The degree of post-impact strength degradation increased with increasing impact velocity and was greater in a partially supported configuration than in a fully supported one. For the fully supported configuration, frontal contact stress played a major role in generating composite damage, while for the partially supported case, both frontal contact and backside flexure stresses were the combined sources of damage generation. The oxide/oxide composite was able to survive high energy $(∼1.3 J)$ impacts without complete structural failure. The degree of relative post-impact strength degradation of the oxide/oxide composite was similar to that of an advanced SiC/SiC composite observed from a previous study, regardless of the type of specimen support. Like the SiC/SiC composite, impact-damage tolerance was greater in the oxide/oxide than in monolithic silicon nitride ceramics for impact velocities $>300 m/s$.

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## Figures

Figure 1

SEM micrographs of oxide/oxide (N720/AS) ceramic matrix composite used in this work

Figure 2

Impact testing apparatus (15)

Figure 3

(a) Two types of target-specimen support used in FOD testing: (i) fully supported and (ii) partially supported (L=20 mm); (b) four-point flexure configuration used in post-impact strength testing with a LVDT placed

Figure 4

Post-impact flexural strength as a function of impact velocity, determined for oxide/oxide composite impacted by 1.59-mm-diameter steel-ball projectiles with two different types of specimen support. As-R represents as-received strength with no impact.

Figure 5

(a) Comparison of post-impact flexural strength as a function of impact velocity between the oxide/oxide (this study) and the MI SiC/SiC composites (21), impacted by 1.59-mm-diameter steel-ball projectiles with two different types of specimen support. (b) Comparison in normalized post-impact strength between the two composites.

Figure 6

1.59-mm-diameter steel-ball projectiles after impact on (a) oxide/oxide at 400 m/s (in full support), (b) oxide/oxide at 400 m/s (in partial support), and (c) AS800 silicon nitride at 350 m/s (in full support) (15)

Figure 7

Frontal impact-damage size as a function of impact velocity for the oxide/oxide composite in fully and partially supported configurations. The data on the MI SiC/SiC composite (21) were included for comparison.

Figure 8

Typical examples of damage showing impact sites and sides of specimens at 350 m/s: (a) fully supported specimen; (b) partially supported specimen. The arrows indicate the impact sites.

Figure 9

Progression of impact damage with velocity in (a) fully supported and (b) partially supported specimens. The vertical arrow indicates a case of increasing impact velocity.

Figure 10

Cross-sectional views of impact sites showing occurrence of cone cracking in (a) oxide/oxide (400 m/s), (b) SiC/SiC (400 m/s), (c) AS800 silicon nitride at 400 m/s (18), and (d) a cone separated from (c). The arrows indicate the impact sites.

Figure 11

Load-deflection curves determined in flexure for both fully and partially supported specimens impacted from 0 m/s to 400 m/s. The curves with zero velocity indicate the as-received specimen with no impact.

Figure 12

Comparison of normalized post-impact strength as a function of impact kinetic energy among the oxide/oxide, the MI SiC/SiC (21), and AS800 and SN282 silicon nitrides (16), impacted by 1.59-mm-diameter steel projectiles in a fully supported configuration

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