Materials Research and Structural Mechanics

Materials research, development, and testing activities at the Institute include formulating and synthesizing new materials, improving materials performance with surface treatments and coatings, evaluating materials under service conditions, and assessing the remaining useful life of critical components and structures. An integrated approach to structural mechanics embraces the analysis, design, and testing of a variety of aerospace, land, and underwater structures for government agencies and commercial clients.

SwRI scientists developed a microelectromechanical system (MEMS) device to study the strength and deformation of thin films on the micro-scale. High-resolution images of the deformed test specimen (right) are used to measure deformation in the thin-film microstructure, allowing the strain levels in the material to be determined for validation of MEMS designs.

In a major effort for the U.S. Department of Energy (DOE), SwRI is leading a project for the design and installation of a pilot manufacturing process for high-volume production of fuel-cell membrane electrode assemblies for transportation applications. The centerpiece of this effort is a vacuum coating unit capable of producing as much as a million square feet of high-performance, ultra-low-catalyst-containing fuel-cell electrodes per year.

SwRI is using its plasma immersion ion processing (PIIP) technology on behalf of a variety of commercial clients. PIIP is a relatively new vacuum technology for the application of hard, wear-resistant coatings. Diamond-like carbon coatings applied to metal forming tools can reduce adhesive and abrasive wear and extend tool life by up to a factor of five. Uncoated tools can require frequent replacement, thus making the product prohibitively expensive.

The U.S. Air Force and its allies have experienced high-cycle fatigue (HCF) incidents in critical aircraft engine components that can severely limit operational readiness. The Institute is working with the Air Force and domestic engine manufacturers to develop improved design methods to eliminate this problem. Methods are being formulated and validated to treat HCF at sharp notches that are geometrically similar to the damage induced in blades from the impact of foreign objects such as gravel, sand, or other runway debris that might be sucked into the engine. Enhanced methods of analyzing and predicting fatigue crack growth in single-crystal nickel alloy turbine blades are also being developed.

Using internal research funds, the Institute is developing a means of measuring mechanical properties of microelectromechanical systems (MEMS) on the wafer level. These measurements could be useful in assessing the durability and reliability of MEMS devices, optimizing fabrication parameters, and enhancing quality assurance. SwRI researchers are conducting strain mapping on the microscopic scale to assess whether the material's microstructure affects the design of MEMS devices.

Significant cost savings could be realized if the risers and flow lines used for deepwater offshore oil and gas exploration could be welded onshore, spooled on a reel, and unreeled at sea during installation. However, the large plastic strains associated with the reeling/unreeling process could result in premature fatigue failure of the risers during service. Shell Deepwater Services, in conjunction with the Institute, is cooperatively funding development of an analytical tool to assess the impact of reeling/unreeling on the subsequent fatigue life of tubular products. Results are consistent with limited service experience, and further experimental validation of this analytical tool is under way.

A new deepwater ocean simulator was designed, fabricated, and built by SwRI to test a variety of offshore components, including subsea valves, tubular goods, flotation materials, and pressure-resistant housings. Measuring 24 feet in length with a 50-inch inner diameter and a wall thickness of 5 inches, the simulator is rated to 6,000 pounds per square inch gauge, equivalent to a depth of 13,280 feet.

Smart mechanical systems could potentially increase the reliability and readiness of military hardware, as well as significantly decrease costs. The Institute is conducting a pilot study, sponsored by the U.S. Air Force Research Laboratory and the Defense Advanced Research Projects Agency, to quantify the potential benefits of integrating sensor information from aircraft engines with physics-based models and probabilistic damage mechanics. These tools would be used to forecast engine problems and predict probability of failure of critical components. Since the probability of engine failure is use-related, researchers are focusing on the potential enhancements of predictions based on actual usage, as well as using assumed versus actual usage, to better forecast future performance. These software tools will be used for equipment life assessment.

Last year, the Institute formed an industrial consortium to provide guidance and financial support for further development of NASGRO, a computer code for fracture mechanics and fatigue crack growth analysis originally developed to assess structural parts of the space shuttle. To date, consortium participants have come from the airframe, rotorcraft, and gas turbine engine industries in eight countries. The Institute organized the consortium under the terms of a Space Act Agreement signed with NASA Johnson Space Center, through which SwRI and NASA will cooperate in enhancing the code and distributing it to government and industry. NASGRO currently has more than 1,000 users in a wide range of industries around the world.

COATLIFE™, a software code developed by SwRI for the Electric Power Research Institute (EPRI) that predicts the oxidation life of aluminide and MCrAlY coatings on hot section gas turbine blades, was successfully validated last year against field experience on several combustion turbines. The code was recently enhanced to predict the thermomechanical fatigue life of coated blades. Further work is under way to model the spallation life of ceramic thermal barrier coatings on airfoils. This algorithm will eventually be incorporated into COATLIFE.

Under sponsorship of the Federal Aviation Administration (FAA), SwRI has developed DARWIN™ (Design Assessment of Reliability With INspection), a software code that predicts the risk of aircraft gas turbine rotor disc fracture caused by low-cycle fatigue loading (takeoff-landing cycles). The software integrates a graphical user interface, finite-element stress analysis results, fatigue crack growth life assessment for low-cycle fatigue loading, material anomaly data, probability of anomaly detection by nondestructive inspection, and inspection schedules. The FAA has stated that DARWIN is an acceptable tool to meet the design target risk for new disk designs specified in its Advisory Circular 33.14. The code is being licensed to aircraft gas turbine engine manufacturers.

For the Pipeline Research Council International, SwRI has developed algorithms and software to enable industry users to compute minimum sampling rates for probabilistic fracture and plastic collapse assessments of girth welds in long segments of gas transmission pipeline. These algorithms are based on a user-specified confidence target for the computed reliability of a pipeline segment, as well as the estimated per-sample costs of obtaining data. The software tool will help those responsible for pipeline integrity maintenance to align flaw assessment procedures with corporate risk management programs.

The Institute continues to be an integral contributor to a joint NASA/U.S. Air Force effort to develop a new aircraft wing structure technology called the Active Aeroelastic Wing (AAW). The objective of the program is to achieve the same aircraft control function with a lighter weight wing structure. SwRI will provide airload predictions for a test wing that will begin flight testing in the summer of 2002 at NASA's Dryden Flight Research Center located at Edwards Air Force Base. Full-scale flight experiments will be conducted on a modified NASA F-18 to gain nonlinear aeroelastic responses from the AAW control effector -- the outboard portion of the wing - that can be used as future design guidelines. The airload predictions will be part of a reference database with which to compare the actual dynamic flight test loads. The Institute will also participate in the flight test data reduction and interpretation for design guidance criteria needed for future applications, such as tailless fighter aircraft.

Corrosion in the C-130 28-foot-long sloping longeron is the aircraft's single biggest airframe reliability and maintainability problem. Grind-out of the corrosion is the standard repair solution, resulting in replacement of the longeron at about 15 years of service. Institute engineers evaluated the original longeron as well as changes in the operating environment, and examined materials available to solve the problem. They then designed and analyzed a splice repair and procured replacement parts. SwRI also served as a liaison between extrusion suppliers, manufacturing vendors, and logistics center engineers to ensure that the finished parts satisfied the requirements of C-130 operators.

For the U.S. Navy, the Institute is replacing aging flight data recorders in selected T-39N aircraft that have been flown since 1991. These aircraft play a key role in the Undergraduate Military Flight Officer Training Program for future weapon systems operators of aircraft such as the F-14, F-15, and F-18. The new flight data recorders, which contain state-of-the-art electronics and components, are being installed to monitor how the aircraft are used in this training environment. Data obtained from the recorders are used for fatigue analysis of the wing, fuselage, and empennage. Quarterly reports document the data collected and the remaining service life of each aircraft. These reports allow the Navy to monitor aircraft usage, project when replacement components are needed, and protect the flight safety of the aircraft.

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