Aerospace & Defense Technology - December 2021 - 28

Tech Briefs
tion, and characterization. The limitations
in pattern-synthesis techniques
have become less of a roadblock as algorithms
have been developed for both
transmit and receive operation. Phaseonly
pattern synthesis techniques exist to
form omnidirectional transmit patterns
with multiple nulls to minimize radiation
in desired directions while still maximizing
transmit power. On receive, directional
patterns with custom sidelobe constraints
may be formed and steered over a
full 360 in azimuth with no significant
degradation to pattern characteristics.
This work was done by W. Mark Dorsey
for the Naval Research Laboratory. For
more information, download the Technical
Support Package (free white
paper) at www.aerodefensetech.com/tsp
under the DAQ, Testing & Sensors category.
NRL-0079
Fatigue Behavior of an Advanced Melt-Infiltrated SIC/SIC
Composite with Environmental Barrier Coating at 1200°C
in Air and in Steam
Because of their low density, high strength and fracture toughness at high temperatures, SiC fiberreinforced
SiC matrix composites are being evaluated for aircraft engine hot-section components.
Air Force Institute of Technology, Wright-Patterson Air Force Base, Ohio
M
odern and future aircraft jet engines
require increased thermal
efficiency to extract the necessary energy
during fuel consumption for high
velocity flight. One way of improving
engine efficiency is through the increase
of the turbine's temperature gradient
or the difference between the
hottest and coldest temperatures in the
engine during operation.
The deficiencies of nickel-based superalloys
or high-performance alloy materials
in turbine engine technologies has
grown apparent as modern turbine engine
hot section operating temperatures
exceed these material's stable operating
ranges. Any additional cooling to the
current systems to prevent melting of
the superalloys would detrimentally
lower the thermal gradient of the engine.
For this reason, novel high temperature
materials which do not require extensive
cooling are necessary for the improvement
of turbine engine technologies.
Ceramic matrix composite (CMC) materials
have been developed as successors
to superalloys. These composites maintain
their properties at high temperatures
due to the nature of the constituent
ceramic materials while also benefiting
from a reinforcement phase, which increases
toughness compared to a monolithic
or bulk ceramic. The accompanying
figure shows general regions of
operating temperatures and specific
strengths for comparison of superalloys,
CMCs, and various other materials. The
28
Intro
Cov
This research has been limited to iden800
CFRP
100
200
400
500
Temperature,
°C
Material Strengths at Various Temperatures - Specific
strength comparison between a variety of materials
including nickel-based superalloys and CMCs in terms
of operating temperature ranges.
weak bonding between the matrix and
reinforcement phases of CMCs prevents
brittle, catastrophic failure exhibited in a
bulk ceramic due to deceleration of crack
propagation and a simulated ductile region
caused by matrix failure prior to reinforcement
failure.
The complexities of composite production
compared to alloy or monolithic
ceramic production lend these materials
to extensive characteristic variation between
processing techniques. Each variation
of material constituent and processing
technique must be characterized to
adequately understand the composite.
Additionally, due to oxidation-prone
constituents that hinder the composite
through oxidation embrittlement and
surface recession, environmental barrier
coatings have been developed to protect
the composite surface.
www.aerodefensetech.com
ToC
+
-
1000
1500
Ti-MMC
Ti-AI
Ti
Steel
Nonoxide CMC
C/SiC, C/C-SiC
SiC/SiC
Ni-base
alloy
Oxide CMC
(WHIPOX)
tification and characterization of a single
CMC composed of silicon carbide matrix
and Hi-NicalonTM silicon carbide reinforcement
fibers processed through meltinfiltration
(SiC/SiC - MI) with a boron
nitride (BN) interphase for weak fibermatrix
bonding. Additionally, the specimens
have been grit-blasted and coated
with a silicon (Si) bond coat and an ytterbium
disilicate (Yb2Si2O7) environmental
barrier coating.
Ten EBC/Hi-N/MI-SiC specimens were
subjected to cyclic fatigue testing at various
maximum stress levels to determine
fatigue life of the specimens in air and
steam at 1200°C along with the retention
of tensile properties if run-out (200,000
cycles) was achieved. This data was compared
to prior research on a set of identical
but uncoated CMC specimens.
A SiC/SiC composite was selected for
research due to the thermal, mechanical,
and chemical stability of silicon carbide.
Thermally, as shown in the accompanying
figure, this CMC maintains
adequate strength at elevated temperatures
which surpasses competing materials.
Mechanically, the composite exhibits
a nearly ductile region prior to
failure despite a fully ceramic composition.
This stems from the prevention of
instantaneous catastrophic failure
through crack prevention. Chemically,
silicon carbide creates a natural protective
oxidation layer at high temperatures
but suffers from oxidation degraAerospace
& Defense Technology, December 2021
A
µ
Specific strength, MPa/(g/cm3
)
È
http://www.aerodefensetech.com/tsp http://www.aerodefensetech.com http://info.hotims.com/79420-922

Aerospace & Defense Technology - December 2021

Table of Contents for the Digital Edition of Aerospace & Defense Technology - December 2021

Aerospace & Defense Technology - December 2021 - Intro
Aerospace & Defense Technology - December 2021 - Sponsor
Aerospace & Defense Technology - December 2021 - Cov1
Aerospace & Defense Technology - December 2021 - Cov2
Aerospace & Defense Technology - December 2021 - 1
Aerospace & Defense Technology - December 2021 - 2
Aerospace & Defense Technology - December 2021 - 3
Aerospace & Defense Technology - December 2021 - 4
Aerospace & Defense Technology - December 2021 - 5
Aerospace & Defense Technology - December 2021 - 6
Aerospace & Defense Technology - December 2021 - 7
Aerospace & Defense Technology - December 2021 - 8
Aerospace & Defense Technology - December 2021 - 9
Aerospace & Defense Technology - December 2021 - 10
Aerospace & Defense Technology - December 2021 - 11
Aerospace & Defense Technology - December 2021 - 12
Aerospace & Defense Technology - December 2021 - 13
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Aerospace & Defense Technology - December 2021 - 18
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Aerospace & Defense Technology - December 2021 - 20
Aerospace & Defense Technology - December 2021 - 21
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Aerospace & Defense Technology - December 2021 - 24
Aerospace & Defense Technology - December 2021 - 25
Aerospace & Defense Technology - December 2021 - 26
Aerospace & Defense Technology - December 2021 - 27
Aerospace & Defense Technology - December 2021 - 28
Aerospace & Defense Technology - December 2021 - 29
Aerospace & Defense Technology - December 2021 - 30
Aerospace & Defense Technology - December 2021 - 31
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Aerospace & Defense Technology - December 2021 - 33
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Aerospace & Defense Technology - December 2021 - 37
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Aerospace & Defense Technology - December 2021 - 39
Aerospace & Defense Technology - December 2021 - 40
Aerospace & Defense Technology - December 2021 - Cov3
Aerospace & Defense Technology - December 2021 - Cov4
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https://www.nxtbook.com/smg/techbriefs/21ADT09
https://www.nxtbook.com/smg/techbriefs/21ADT08
https://www.nxtbook.com/smg/techbriefs/21ADT06
https://www.nxtbook.com/smg/techbriefs/21ADT05
https://www.nxtbook.com/smg/techbriefs/21ADT04
https://www.nxtbook.com/smg/techbriefs/21ADT02
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