Ceramic Analysis
In the continuing quest for improved performance of aerospace
systems, designers are exploring alternative materials that are
stronger yet lighter than metals and have superior resistance
to high temperatures. Among leading candidates are ceramics,
which have already found service in aerospace propulsion systems
in such high temperature Earth applications as diesel/turbine
engine components and heat exchangers. They also offer performance
benefits in products subjected to a lot of stress or wear, such
as nozzles, valves, cutting tools, grinding wheels, bearings,
and even artificial knee and hip joints.
 A
CARES/LIFE plot shows stress levels (red/yellow highest, blue/green
lowest) on a turbine blade.
Ceramic properties have improved a great deal in recent years
due to advances in processing and composition, but they are inherently
brittle and that leads to low strain tolerance and low fracture
toughness. In addition, ceramic parts vary greatly in strength
behavior; apparently identical parts can have vastly different
fracture strength due to the variable severity of flaws in the
materials. From the beginning of ceramics research, it was apparent
that there was a need for a way of determining-in a product's
design phase-the effects of stress and fatigue on a part, identifying
all potential failure modes, and predicting lifetime capability.
This was a challenge of first magnitude.
After more than 15 years of effort, Lewis Research Center
provided a solution, a software package known as CARES/LIFE that
accurately predicts the performance of brittle structures over
time. The importance of this development is underlined by the
multiple awards presented to the Lewis Research Center development
team: a 1995 R&D 100 Award from R&D Magazine as one of
the most significant technological advances of the year; a NASA
Software of the Year Award; and the Federal Laboratories Consortium
Award for Excellence in Technology Transfer. More than 300 organizations
worldwide have used the CARES program in design of such widely
diverse products as turbojet engines, valves for auto and truck
engines, computer chips, cathode ray tubes and glass panels for
office buildings. Some 65 companies are using the CARES/LIFE
versions of the code.
Philips Display Components Company used CARES/LIFE to analyze
pressure forces on television tubes.
Lewis Research Center began work on the program in the late
1970s to serve the ceramics development needs of NASA, the Department
of Energy (DoE), other government agencies and industry. At that
time, no code for predicting ceramic durability existed. John
Gyekenyesi, head of Lewis' Structural Integrity Branch, was assigned
to devise one. Members of the team who shared the Software of
the Year Award with Gyekenyesi include Lesley A. Janosik, Noel
N. Nemeth, Lynn M. Powers and Jonathan Salem.
The CARES (Ceramic Analysis and Reliability Evaluation of
Structures) program they developed offers a cost effective means
for simulating tests of ceramic components; it enables a designer
to test a variety of configurations for probability of failure,
and to adjust the structure's geometry to minimize the predicted
failure or maximize durability. The newest version of the software-CARES/LIFE,
released in 1995-has the added capability of lifetime prediction.
Among the examples of the code's utility,
- Solar Turbines Incorporated, San Diego, California is using
CARES/LIFE in a DoE-sponsored development program that seeks
significant performance gains by replacing metallic hot section
parts in a gas-fired industrial turbine with ceramics; ceramics
last longer, offer more resistance, reduce friction and weigh
less.
- Philips Display Components Company, Ann Arbor, Michigan analyzed
glass television tubes with CARES/LIFE to determine the forces
placed on the outside of an evacuated tube and the possibility
of tube implosion. The research analysis concluded that the possibility
of tube implosion is nearly zero and that an implosion protection
band reduced maximum principal stress by 15-20 percent and further
reduced the probability of failure.
- The CARES software is in use at AlliedSignal Turbocharging
and Truck Brake Systems, Torrance, California, where the company
has developed automotive turbocharger wheels for a diesel engine,
the first design and large-scale development of ceramic turbochargers
in the U.S. AlliedSignal has delivered more than 1,700 units
to Caterpillar Tractor Company, Peoria, Illinois for on-highway
truck engines.
- Among a number of automotive engine applications, TRW Inc.'s
Automotive Valve Division is using CARES software to design ceramic
poppet valves and engine components for passenger cars. General
Motors Corporation is similarly using CARES for automotive applications.
CARES and CARES/LIFE were developed in the public domain and
thus are readily available to industrial firms. The codes are
distributed through NASA's Computer Software Management and Information
Center (COSMIC)® at the University of Georgia.
TRW Inc. used CARES to design ceramic poppet valves
and engine components.
AlliedSignal's development of automotive ceramic
turbocharger wheels was aided by CARES software.
®COSMIC is a registered trademark of the
National Aeronautics and Space Administration.
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