Materials Research and Structural Mechanics

The Institute maintains a vigorous program in materials research, development, and testing for commercial and government clients. The program encompasses the entire life cycle of materials and includes formulation and synthesis of new materials, evaluation of performance under service conditions, and assessment of remaining useful life of existing components and structures. In the last area, the Institute staff has formulated pioneering mathematical methods for determining life-extension protocols.

The Institute's Ion Beam Surface Modification facility provides a capability for producing many kinds of ion beam- assisted coatings of metallic or ceramic composition, and for applying diamond-like carbon (DLC) coatings. These coatings can be applied to a wide variety of components, including orthopedic implants, engine parts, and cutting tools, to reduce wear, friction, and corrosion. Characterization of the coatings by laser Raman spectroscopy and by ion beam analysis confirms their composition and amorphous microstructure. Electrical measurements have shown DLC coatings to be highly conducting, unlike plasma-deposited carbon films. Work is in progress to increase conductivity by doping, for instance with boron, for use in solar cell applications. The next phase of ion beam facility development will include installation of a high- energy (100 keV) plasma source, which will make it possible to modify the surface structures of metals, ceramics, and polymers by direct ion implantation.

Engineers are investigating the use of fiber optic sensors for damage assessment, repair, and maintenance of airframe and aircraft engine components fabricated from advanced organic polymeric composites. This project is aimed at development of the first portable spectrometer and associated fiber optics to probe the chemical and physical states of in-service composite materials. A prototype system for field and depot use will be built at the Institute and evaluated at the Air Logistics Center at Tinker AFB, Oklahoma.

A program is under way for the U.S. Air Force Wright Aeronautical Laboratories to develop unique closed-loop process control systems for the manufacture of nonmetallic and polymeric composite structures such as airframe and engine components for advanced fighter aircraft. Initial research focuses on control of chemical vapor deposition of mixed oxides on the surface of the inorganic fibers used in high-temperature components. This work involves the development and refinement of fiber optic Raman spectroscopy for in situ measurement of surface stoichiometry, film thickness, and other process variables.

The Institute's gas turbine materials and coatings program continues to grow. SwRI operates the Materials Center for Combustion Turbines for the Electric Power Research Institute (EPRI). The center provides technology and expertise to EPRI- member utilities in the management of turbine hot section components. Research activities include the development of software to enable determination of remaining life in turbine blades and static vanes, life modeling and nondestructive evaluation of thermal barrier coatings for turbine disks and blades, and development of methods for the repair of thermal barrier coatings.

Project is under way for the Federal Aviation Administration to develop a probabilistically based damage tolerance design code to augment the current safe-life philosophy for life management of commercial aircraft gas turbine rotors and disks. Four aircraft gas turbine manufacturers will collaborate with SwRI and will incorporate the code into their design systems. Issues addressed will include characterization and detection of anomalies in titanium alloys, the movement of these anomalies during forging, and the initiation and growth of flaws due to the presence of anomalies. Results will be incorporated into an integrated probabilistic design code.

Materials issues are central to several biomedical device problems being examined by Institute researchers. Artificial heart valves are subject to a number of materials-based problems that can result in valve failure. A molecular modeling-based study has revealed the initial mechanisms leading to the calcification of polyether urethane materials via a complexation mechanism whereby the calcium is attracted to and trapped by the oxygen in the polymer. Lifetime prediction studies of pyrolytic carbon heart valve materials have led to the development of an acoustic emission system for detecting crack initiation and growth during controlled stress testing of assembled heart valves. This project is expected to have a significant effect on the quality control and performance of future heart valves.

Institute scientists are using an acoustic emission-based system to detect the nucleation and growth of cracks in artificial heart valve materials. The technology may be used for production line quality assurance during manufacture of heart valve components.

A number of projects have established critical factors regarding the failure mechanisms of orthopedic implants. These discoveries have led to projects that address materials-based solutions. For example, atomic force microscope images of hydrated biofilms are being studied to gain a new understanding of how certain biomaterials contribute to chronic infections associated with medical implants, and how the infections might be eradicated by modifying implant surfaces. Other biomaterials research involves coatings development and characterization, novel orthopedic and dental materials, and autogenic materials for soft tissue augmentation and implants.

Replacement and repair of corroded gas transmission pipeline sections represent a considerable cost to the gas industry. Under contract to the Gas Research Institute (GRI), SwRI evaluated a composite overwrap that reinforces a damaged pipeline and thereby restores its structural integrity. Full-scale and coupon-sized tests of the composite material and in-depth mechanical analyses of a reinforced pipeline section provided results that were instrumental in securing U.S. Department of Transportation approval for use of the repair process. A PC-based computer program, which determines defect sizes that can be safely reinforced with the composite overwrap, was developed for use by the gas industry.

A program sponsored by the Gas Research Institute, the Department of Energy, the Department of Transportation, and cylinder and vehicle manufacturers is using infrared thermography to detect impact damage and long-term degradation in composite fuel cylinders for natural gas vehicles. Thermography is an effective investigative technique because it can detect subsurface damage and it allows a large area to be studied at one time. In this thermal image, a technician holds a damaged cylinder in which impact damage is seen as a "hot spot" near the center.

During the past year SwRI conducted more than 50 failure investigations for the power generation, aerospace, petrochemical, medical, manufacturing, and transportation industries. One such investigation involved the analysis of a liquid oxygen storage tank pipeline that ruptured and exploded, scattering debris throughout an industrial plant. A study of the debris pattern and the fracture surface, as well as chemical analyses of surface deposits, determined that the failure resulted from rapid overpressurization caused by hydrocarbon intrusion and detonation. As a result, the client was able to make changes in the piping system to prevent further mishaps.

Under contract to NASA, the Institute is developing advanced elastic-plastic fracture mechanics technology to support improved component reliability for the space shuttle main engine and for advanced propulsion systems for the planned X-33 reusable launch vehicle. More accurate than existing linear elastic fracture mechanics methods, the new technology addresses the severe cyclic thermal and mechanical loads placed on engine components during flight. The elastic- plastic methods allow improved design and interpretation of preflight structural proof testing and can also be used to predict flaw growth rates during actual service, enhancing safety while avoiding unnecessary and expensive hardware replacement. The Institute is implementing the new technology into software tools for use by NASA and NASA contractors.

Understanding how geological materials behave over time when exposed to elevated temperature and pressure is critical in assessing the structural integrity of underground repositories such as the Waste Isolation Pilot Plant in Carlsbad, New Mexico, designed to store transuranic low-level waste. In a project sponsored by the U.S. Department of Energy and Sandia National Laboratories, SwRI engineers developed a mechanistically based model that allows accurate prediction of the long-term creep, fracture, and damage-healing behavior of rock salt. When incorporated into a finite-element structural analysis code, this model predicts the damage evolution and failure time observed experimentally in underground room tests.

Microbiologically influenced corrosion (MIC), a phenomenon that costs industry 40 to 50 billion dollars annually in damaged components, is the focus of an Institute internal research program aimed at a better understanding of MIC mechanisms as a means to detect and control such damage. Electrochemical tools are being used to study the response of steels, stainless steels, and other engineering alloys exposed to damaging bacteria. Based on this program, GRI has contracted SwRI to study MIC in gas transmission pipelines.

Full-scale fatigue tests and post-test teardown inspections are conducted at SwRI to evaluate the structural performance of the U.S. Air Force T-38 wing design. A metallurgical examination of the wing lower skin determines potential critical fatigue locations.

The Institute is working on several GRI-funded projects to evaluate the use of polyethylene (PE) pipe, which is fast becoming the material of choice for gas distribution pipelines. PE pipe is being tested for modified slip lining, a method used to repair degraded steel or cast iron pipes. It is also being investigated for horizontal boring applications, and the Institute is formulating guidelines for consequent pipe installation, operation, and life expectancy.

An SwRI-developed pipe repair tool and internal seal allow polyethylene gas distribution pipelines to be repaired without loss of service. For high-pressure systems where shutoff is required, the repair can be made and gas service restored in less than one minute.

Institute-developed PE repair technologies are designed to increase reliability while reducing costs. A new polyethylene repair material, called PERM, reduces or eliminates the need to scrape the surface of a pipe before fusion. An innovative repair technique employs a standard sidewall tool to spin a disk of PERM against damaged PE pipe, where frictional heat melts the PERM and the pipe and fuses the disk over the defect. The spin friction tooling and spin fittings may be used on any size pipe larger than the minimum pipe diameter specified for that fitting. For certain hole sizes and operating pressures, spin friction repairs may be made with gas flowing in the pipe.

SwRI engineers designed a fixture for testing mateable electrical connectors and hydraulic couplers in conditions simulating deep submersion. The connectors and couplers play a critical role in the reliable control of subsea production systems used by the offshore oil industry.

The Institute is an active participant in DeepStar, a cooperative program of the offshore oil industry that is developing cost-effective systems for deep water installations in the Gulf of Mexico. SwRI is determining the suitability of mateable electrical connectors and hydraulic couplers for use in deep water, where they will play a critical role in the reliable control of subsea production systems. SwRI engineers tested the components in a specially designed fixture in the SwRI ocean simulation laboratory, where conditions at depths to 8,000 feet can be simulated.

The Institute maintains a full range of structural design, analysis, and testing capabilities to support a variety of aircraft for flight safety assessment and service life extension programs. In one program, engineers installed flight data recorders to gather usage severity data in NASA T-38 astronaut training aircraft. For the U.S. Air Force, SwRI conducted a full-scale fatigue test and post-test teardown inspection to evaluate structural performance of the T-38 trainer aircraft wing. A structural modification kit was designed and has been installed that will extend lifetime usage into the next century. The Institute is also assessing the structural integrity of F-5 fighter and T-37 trainer aircraft operated by allied governments. Flight usage surveys were completed for F-5s in four foreign countries; another survey will begin in early 1996.

In a project for the Railway Progress Institute/Association of American Railroads (RPI/AAR) Tank Car Safety Program, SwRI is transferring state-of-the-art damage tolerance analysis (DTA) technologies, customarily used in the aircraft industry, to the railroad industry. SwRI engineers are instructing RPI/AAR personnel in the use of DTA to establish periodic inspection intervals to detect fatigue cracking prior to failure and to assess the structural integrity of tank car stub-sills, which accommodate the coupler and draft gear and transfer coupler forces to the tank car body.

Institute engineers are integrating the SwRI-developed NESSUS probabilistic analysis program and a commercial finite element program to assess the probability of cervical spinal injury. These injuries typically occur as a result of severe accelerations, such as when a pilot ejects from an aircraft. Shown is a cervical spine finite element model developed for the program by Tulane University that includes vertebrae, discs, and ligaments.

Probabilistic mechanics activities at SwRI encompass a wide variety of engineering disciplines. A methodology that will provide a basis for assessing the probability of injury to cervical spine components as a result of impact is being developed for the Naval Biodynamics Laboratory. This project is part of a U.S. Navy effort to build an anatomically and kinematically correct model of the spine.

High performance computing, including parallel computing techniques and scientific visualization, is having a significant impact on computer simulations performed by Institute staff in a variety of disciplines. The area of computational mechanics is at the heart of this effort in terms of the development of new techniques and algorithms for solving systems of equations describing physics for many applications. These applications range from large-deformation structural dynamics, to fluid dynamics, to chemistry and chemical kinetics. Institute researchers have devised alternative strategies for large-scale computations that require hundreds of hours of computation time, even when run on costly supercomputers. The core element of these strategies is the use of smaller processors, such as workstations, coupled to create a single multiple processor computer. Considerable progress has been made in the development of application software using this and other parallel computing strategies, which are faster and more cost-effective than conventional techniques. One example of successful implementation is the reduction of computing time for a code used to simulate the lubrication and performance of bearings in automotive applications. The new parallel code produces execution times 40 times faster than the original code.

Engineers designed and fabricated a ship hull structural model for the Defense Nuclear Agency (DNA) to study the effects of shallow water mine impact. The Institute has designed and built models for the U.S. Navy and DNA for more than 20 years.

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