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Research Papers: Gas Turbines: Ceramics

Foreign Object Damage in an Oxide/Oxide Ceramic Matrix Composite Under Prescribed Tensile Loading

[+] Author and Article Information
Nesredin Kedir, David Faucett, Luis Sanchez

Naval Air Systems Command,
Patuxent River, MD 20670

Sung R. Choi

Naval Air Systems Command,
Patuxent River, MD 20670
e-mail: sung.choi1@navy.mil

1Corresponding author.

Contributed by the Ceramics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 6, 2016; final manuscript received July 12, 2016; published online September 20, 2016. Editor: David Wisler. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Eng. Gas Turbines Power 139(2), 021301 (Sep 20, 2016) (8 pages) Paper No: GTP-16-1314; doi: 10.1115/1.4034360 History: Received July 06, 2016; Revised July 12, 2016

Foreign object damage (FOD) behavior of an N720/alumina oxide/oxide ceramic matrix composite (CMC) was characterized at ambient temperature by using spherical projectiles impacted at velocities ranging from 100 to 350 m/s. The CMC targets were subject to ballistic impact at a normal incidence angle while being loaded under different levels of tensile loading in order to simulate conditions of rotating aeroengine airfoils. The impact damage of frontal and back surfaces was assessed with respect to impact velocity and load factor. Subsequent postimpact residual strength was also estimated to determine quantitatively the severity of impact damage. Impact force was predicted based on the principles of energy conservation.

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Figures

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Fig. 1

Examples of FOD in hot-section hardware in aeroengines: (a) micro FOD in TBCs by a miniature particle, probably by a molten metallic droplet; (b) intermediate FOD probably by a pointed particle causing deformation and compaction of TBCs/substrate; and (c) significant FOD by big metallic objects [1]

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Fig. 2

Typical microstructure of an N720/alumina oxide/oxide CMC used in the current work

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Fig. 3

Configuration and setup of tensile test specimen in FOD testing under tensile preload for an N720/alumina oxide/oxide CMC. The impact site was at x = y = z = 0. The FPR represents a tensile preload applied during impact experiments. The “V” indicates the impact velocity.

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Fig. 4

Impact damage morphology generated in impact sites (front sides) and back sides as a function of impact velocity and load factor (α) in an N720/alumina CMC subjected to impact by 1.59 steel ball projectiles. The direction of applied preloads is shown as a double arrow in the right above.

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Fig. 5

Example of stress–strain curves of impacted specimens with no tensile preload, determined in postimpact strength testing for an N720/alumina CMC impacted by 1.59 mm steel ball projectiles. The AsR denotes the as-received test specimen.

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Fig. 6

Results of postimpact strength as a function of impact velocity at different levels of load factor (α) for an N720/alumina CMC impacted by 1.59 mm steel ball projectiles. The solid lines represent the best fit. The AsR denotes the as-received strength of the material.

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Fig. 7

Postimpact strength as a function of load factor (α) at different levels of impact velocity for an N720/alumina CMC impacted by 1.59 mm steel ball projectiles. The solid lines represent the best fit. The AsR denotes the as-received strength of the material. The offset from “zero” at α = 70% was made for clarity of plotting.

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Fig. 8

Schematic showing an impact event in the tensile-grip support used in this work: (a) overall; (b) idealized impact event of an oxide/oxide CMC target by a spherical steel ball projectile. The L and δ represent, respectively, unsupport (span) length and target deflection by impact. The py denotes the contact yield stress, d and z are damage sizes, D is the projectile diameter, and F and V are impact force and velocity, respectively.

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Fig. 9

SEM image of an indent made on an N720/alumina CMC by a 1.59 mm steel ball projectile with an indent force of 980 N

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Fig. 10

Indent size as a function of indent force determined in an N720/alumina CMC indented by 1.59 mm steel ball projectiles. The inset describes the indent diameter (di) and depth (zi). The solid lines represent the best fit.

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Fig. 11

Contact area as a function of indent force determined in an N720/alumina CMC indented by 1.59 mm steel ball projectiles. The solid lines represent the best-fit regression line. The inverse of the slope corresponds to the value of contact yield stress, py.

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Fig. 12

Predicted impact force as a function of impact velocity for the tensile-grip support in an N720/alumina CMC impacted by 1.59 mm steel ball projectiles. The impact-force prediction for full support was made for comparison. The “e” represents coefficient of restitution.

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Fig. 13

Predicted impact damage size (d) as a function of impact velocity for tensile-grip support in an N720/alumina CMC impacted by 1.59 mm steel ball projectiles. The solid line represents the prediction. The full-support prediction and experimental data were also included for comparison.

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