Summaries of Presentations made at the May 2000 Meeting of the NDE Communications Group, Materials Technology (MatTec) Subcommittee, National Science and Technology Council (NSTC)

A brief overview of the US Army Research Laboratory chain of command was presented to show where NDE technical expertise exists in the ARL organization. Technical NDE inputs were provided from ARL by two directorates: Vehicle Technology Directorate (VTD), Structural Mechanics Division at NASA Langley Research Center (LaRC), Hampton VA and Weapons and Materials Research Directorate (WMRD), NDE Group at Rodman Laboratories, Aberdeen Proving Grounds, Aberdeen MD. An additional technical NDE input was provided by the Aviation Applied Technology Directorate(AATD), which is not part of ARL.

The briefing given to the MatTec Group was project-related rather than programmatic since the NDE work of the Army is on a small scale compared to the other services. Ten (10) projects were overviewed. VTD projects: (1) Ultrasound Generation Using a Modulated Diode System, (2) Advanced NDE Sensor Technologies for Contamination Measurement of Oils and Fuels, (3) In Situ Thermographic Testing of Composite Tension / Torsion Samples, (4) Nonlinear Ultrasonic Inspection for fatigue Damage, (5) Microwave NDE of Composite Materials. WMRD projects: (1) Acoustography, (2) Characterization of Induced Manufacturing Defects, (3) Environmental Effects on the Durability of Advanced Composites, (4) X-ray Computed Tomography. AATD project: Computer Aided NDE Inspection and Repair Disposition.

Dr. Ignacio Perez from the Naval Air Warfare Center at Patuxent River, MD presented the Navy’s NDE R&D program representing Mr. Kelly from the Office of Naval Research (ONR) who was scheduled for travel at the time of the meeting. In an era of tight budgets, careful consideration has to be placed in the programs that are funded making sure that they address the most critical problems that face the Navy and that they provide the largest return on investment. It is also desirable that this limited number of resources be leveraged against other programs (such as MANTEC, SBIR, SERDP, …) to accelerate the execution and transition of the technology.

The main focus of the Navy’s NDE program is in areas relating to our aging assets (corrosion and cracking) and issues addressing inspections under highly attenuative materials. Work in this area has been leveraged with various SBIR programs. The Naval Surface Warfare Laboratory (NSWC) and Naval Air Warfare Laboratory (NAWC) have been successful in winning a Strategic Environmental Research and Development Program (SERDP) to evaluate and adapt three technologies (Ultrasonic Imaging, Thermographic Imaging and Near Field Microwave Scanning) for their viability as NDE tools for the detection of cracks and corrosion under coatings in aircraft and ground vehicle applications. This is a two-year program and initial results are very encouraging.

NSWC has had success in investigating various approaches (near and far field microwave method and ultrasonic methods) to inspect large thick composite structures like the Advanced Enclosed Mast System (AEM/S) and thick phenolic composites addressing delamination, porosity and bond quality issues. NSWC is also transitioning a multichannel signal classification system. This technology was first applied to signal classification of eddy current data and is now being transitioned to industry via a MANTEC program.

NAWC showed progress in areas of thermographic imaging and ultrasonic imaging. These technologies are being developed in conjunction with two SBIR programs. Thermographic inspection results obtained by engineers at NADEP Cherri Point showed a unique application of this technique. In this application, internal cracks developed in the foam material between the spar and the skin of the propeller can be detected thermographicaly without requiring disassembly. In the area of health monitoring, various programs using fiber sensor technology were presented. Areas of interest were Bragg Grating (BG) technologies for strain monitoring, birefringent fibers with BG for bond line monitoring, Long Period Grating sensors for chemical monitoring.

NDE or nondestructive evaluation is an attempt to determine the state or condition of a material/structure in a manner that leaves the material/structure undisturbed by the measurements. For the most part NDE has its basis in nondestructive material characterization. The Naval Research Laboratory (NRL) is the Navy’s corporate laboratory and is tasked primarily to perform basic and applied research. Many of the programs at NRL incorporate some form of nondestructive material characterization. Dr. Mignogna presented vignettes of a few of the programs that incorporate nondestructive material characterization. Some programs are very closely related to NDE, two examples are; Remotely-Queried Embedded Microsensors (presented), for strain and/or temperature monitoring of structures and a Condition Based Maintenance (CBM) program on optically monitoring debris in lubricating oil (not presented). Other programs make use of ultrasound, NMR, optics, x-rays and thermal imaging to name a few measuring methods. Modeling of materials and the interactions of interrogating energy has also been explored.

Summary of presented vignettes:

Remotely-Queried Imbedded Sensors: Very small temperature and/or strain sensors were imbedded in composite materials. The sensor packages contained all the necessary components to receive energy from a remote device, make a measurement and transmit the measurement back to the remote power supply/receiver combination.

Athermal Annealing: Doped silicon wafers (100 mm diameter, 0.5 mm thick) were subject to a focused, pulsed 30 Joule laser beam. The beam generated a mechanical wave in the wafer that annealed a 10 mm diameter area, centered on the laser spot. The object of the program is to understand the phenomena and hopefully enlarge the annealed region.

In-situ Corrosion Monitoring System: An in situ methodology to measure the remaining thickness due to corrosion of liquid storage tank bottoms was presented. The storage tank materials are, usually, common ferritic steels. The patented methodology is based upon ultrasonic spectral frequency tracking. The measured acoustic frequencies were proportional to the remaining thickness.

NMR: Nuclear Magnetic Resonance was applied to planar and spectroscopic imaging. In addition, imaging of surfaces was enhanced using optically-pumped ¹²⁹Xe. ¹H Magic Angle Spinning NMR was used to investigate the miscibility in polystyrene nanogels. Nuclear Quadrupole Resonance was applied to explosives and narcotic detection.

Ultrasonic Wave & Transducer Field Visualization: Parallel computer finite difference computations were experimentally visualized for a two-dimensional case involving two different materials including a couplant layer, with excellent agreement. A three dimensional forward computation was also shown. The predictive capabilities of the parallel computations were applied to a piezoelectric transducer array and supported with experimental measurements.

NTIAC continues to focus on the new NDE paradigm where NDE technology is utilized to meet DoD and other government agency needs:

• For product and process design and optimization
• For on-line manufacturing process control
• For smart/intelligent structures and systems
• For in-plant and after-manufacturing process control
• For traditional in-service inspection

In response to the new paradigm, there is increased emphasis at NTIAC for NDE to assure the readiness and preparedness of weapons systems and equipment used by the warfighter; to extend the useful life of aging assets; and to provide a basis for condition based maintenance decisions. In line with this direction, NTIAC will participate in two upcoming Defense Science and Technology Seminars on Emerging Technologies - in June on "Nondestructive Evaluation of Aging Aircraft" and in July on "Condition Based Maintenance/Predictve Diagnostics". This seminar series was initiated in the fall of 1998 by Dr. Delores Etter, Deputy Under Secretary of Defense (Science and Technology) to promote dialog among military leaders, members of the Defense Science and Technology community, and leading researchers from industry and academia on topics of growing interest and importance to the DoD. NTIAC prepared a special issue May Newsletter devoted to NDE of Aging Aircraft and special promotional flyers on aging aircraft and condition based maintenance. NTIAC displays at both seminars will feature NTIAC's role in these important NDE intensive technology areas.

NTIAC's Technical Area task (TAT) activities continue to increase. TATs provide funding for laboratory research as well as for assessments of various NDE technologies. Seven TATs have been completed and six TATs are in progress on the following topics:

• NDE of Submarine Towed Arrays
• Microwave NDE for Corrosion Under Paint
• NDE of Submarine Composite Transducer Brackets
• Nondestructive Vibrational Testing of Submarine Composite Components
• NDE of High Pressure Aluminum Gas Cylinders
• NDE of Magnetic Switches for the Vertical Launch System

Additional TATs expected to start shortly include:

• NDE of Adhesive Bonds State-of-the-Art Report
• NDE for On-Line Process Control of Single Crystal Tungsten Rods
• Program Plan for POD of NDE Techniques and Applications
• NDE of Composite High Pressure Gas Cylinders

NTIAC is currently working on the following three new technical publications which are expected to be completed by the end of the calendar year:

• NDE of Adhesive Bonds (State-of-the-Art Report)
• NDE for Condition Based Maintenance (Critical Review)
• Probability of Detection for NDE (Technology Assessment)

Potential publication topics for FY01 include:

• Thermography NDE (State-of-the-Art Report)
• Bragg Grating Fiber Optic Based NDE (Technology Assessment)
• NDE and Characterization of Nanostructure Materials (Technology Assessment)
• Surface Wave NDE (State-of-the-Art Report)

Additional resources have been devoted to the NTIAC bibliographic database input activity in order to eliminate a backlog of documents that had accumulated. As a result, between January and June, over 1,600 citations were added to the database which now totals over 60,000 documents. A number of enhancements have been made to the NTIAC web site including: adding a new search engine; providing new documents in 3 formats, HTML, Word, and PDF, to support a wider audience; and undertaking an aggressive campaign to improve NTIAC site rankings. Several initiatives are underway at the IAC Program Office that affect NTIAC. These include the development of strategic goals and performance measures in conformance with the Government Performance & Results Act; development of a new IAC Directory; and converting IAC document holdings to electronic text for full text information searching.

For more information on NTIAC visit our web site at www.ntiac.com; send email to info@ntiac.com; or call (800) NTIAC39.

This paper provides a summary of the Federal Highway Administration's program for developing NDE technologies for the inspection and evaluation of the highway infrastructure. This program is designed to address key goals in the FHWA National Strategic Plan, including the improvement of the mobility and productivity of the interstate highway system. New technologies that can assist in the evaluation of bridge condition to ensure safety and promote efficient maintenance strategies are developed at the NDEVC, and studies that determine the reliability of NDE technologies are conducted.

Since the inception of the National Bridge Inspection Standards (NBIS), adopted in April of 1971, the periodic inspection of highway bridges has relied largely on visual inspection to provide critical information on the condition and safety of the nation’s bridges. During this period, advances in nondestructive evaluation (NDE) technologies have improved the tools available for inspection, however, few technologies have been widely implemented as part on routine inspection procedures. The emerging use by state transportation agencies of bridge management systems (BMS) to assist in the systematic evaluation of the bridge inventory requires more detailed and quantitative information on the condition of bridges. To make these new BMS tools most effective, increased use of quantitative NDE technologies is required in the bridge inspection process.

The goal of the NDE Validation Center is to improve the state of the practice for highway bridge inspection. The center is designed to act as a technical resource in support of State transportation agencies, academia and industry involved with the development of new NDE tools for the evaluation of highway bridges. The NDEVC provides State highway agencies with independent evaluation and validation of NDE technologies, develops new NDE technologies, and provides technical assistance to States exploring the use of these advanced technologies.

The Center is comprised of three elements; the NDE laboratories, sections of bridges containing defects known as component specimen, and field test bridges. The NDE laboratories act as the nucleus of the NDEVC, providing a facility for the development and testing of NDE technologies. The laboratories include a structural loading floor for constructing mock-ups of field conditions, a radiological laboratory used for creating X-ray images of defects, a computed tomography facilitiy for characterizing materials , and an instrumentation laboratory used for manufacturing prototypes and developing new NDE tools.

The component specimens provide realistic specimens for the development of new NDE technologies. Component specimens at the NDEVC include sections of bridge decks containing delaminations, welded details containing cracks, cracked bridge pins, pre-stressed box beams containing corroded and broken strands, cracked sign supports, and other specimens with characteristic forms of deterioration.

Five decommissioned highway bridges are used to evaluate NDE methods under realistic environmental conditions. Two steel bridges that are open to traffic and fully instrumented are used to test NDE methods associated with live loading, such as new instrumentation for global bridge monitoring. These bridges are critical to evaluating the effect of restricted access, structure geometry, surface conditions, platform stability, and human factors on the application of NDE methods during normal bridge inspections. These test bridges provide the NDEVC with a unique ability to evaluate NDE technologies under the same conditions that normal bridge inspections are typically conducted, providing a powerful tool in the evaluation process.

A study is currently being conducted to evaluate the reliability of bridge inspections. This performance study includes teams of bridge inspectors from around the country traveling to the NDEVC to perform inspections on the test bridges associated with the center. Twenty-six states volunteered to send a team of two inspectors to participate in the study. As part of the study, the inspectors were required to inspect seven highway bridges of varying design and condition. Ten different inspection scenarios were utilized to evaluate various approaches used by State transportation agencies to inspect bridges. Human factors, such as training, experience and attitude, were evaluated through a series of questionnaires administered by the NDEVC staff prior to and during the performance of the inspections. This portion of the study was completed in October, 1999, and detailed results will be available in the year 2000.

Currently available methods for evaluating bridge decks include visual inspection of the deck condition, sounding a bare deck with a chain or hammer, measuring the half-cell potential of the deck , and taking cores. All these methods may require lane closures and have limited ability to determine the internal condition of the deck over the entire deck area. Additionally, these methods are not effective at accurately determining the exact location and extent of delaminations in a bridge deck, and are difficult to apply rapidly to large number of bridge decks. Other technologies, such as the infrared thermography and existing ground penetrating radar (GPR) systems, are also sometimes used for the evaluation of bridge decks. These technologies have not satisfied the need to for rapid, quantitative bridge deck assessment. Infrared thermography is limited by environmental conditions and has difficulty evaluating decks with asphalt overlays. Existing GPR systems require significant expert analysis to effectively evaluate deck conditions, and have had difficulty providing fast and reliable results that satisfy the needs of State highway agencies.

To address these needs, the FHWA has funded the development of the HERMES (High Speed Electromagnetic Roadway Measurement and Evaluation System) by the Lawrence Livermore National Laboratories (LLNL). The goal of the HERMES project is to develop a GPR system that can reliably detect, quantify and image delaminations in bridge decks. The system is designed to operate at normal highway speeds, to eliminate the need for lane closures.

The HERMES system is comprised of a computer workstation and storage device, survey wheel, control electronics and array of 64 antenna modules or transceivers, mounted in a towable trailer. The most unique design feature of the HERMES is the antenna array. The arrangement of the transceivers gives samples across a 2 m width of the deck at 3 cm intervals at a speed of 20 mph, 6 cm intervals at 60 mph. The density of data enables synthetic aperture radar techniques to be used in the processing of the data, and two and three dimensional images can be produced. HERMES uses ultra-wide band microwave sources developed by LLNL that produce signals with a frequency content ranging from 0.5 to 5 GHz.

The prototype system was delivered to the FHWA in October of 1998, and field testing of this system was conducted in cooperation with state transportation agencies. The goal of the field testing program was to fully evaluate the prototype system, and identify required improvements for a second generation system.

The HERMES system has garnered attention from many sources. The State of California is convinced that this new technology has the potential to provide a cost saving tool that can change the way bridge decks are evaluated, and initiated a effort to continue development of the system with funding from State transportation agencies. Twenty States agreed to participate in the study, and help fund a project to redesign radar antennas in the system to increase bandwidth in an effort to increase sensitivity to thin delaminations in bridge decks.

Applications for a laser bridge deflection system have been developed that can reduce the cost of the load rating bridges. The laser system, developed under contract for the FHWA, uses a frequency modulated laser to measure distances over a range of up to 30 meters. A computer controlled scanning system controls the laser and allows the system to scan over a large area of a structure. Measurement resolutions of less than 1 mm are possible with the system, and no special targets or surface preparations are required. The NDE Validation Center has developed a series of applications for this technology for making measurements of deflections for large structures. This helps reduce the cost of bridge load rating, and provides more information than is typically available from traditional instrumentation. With a range of 30 meters, the laser system is also capable of measuring deflections of bridges crossing above open traffic lanes, eliminating the need for lane closures.

Other applications of this technology that have been developed at the NDEVC include deflection measurements of large bridge piers under load, and measuring out-of-plane displacements for steel plate girders.

A critical element in the evaluation of highway bridges is determining the distribution of loading in the bridge, and evaluating the stress levels in load carrying members of the bridge. This is typically accomplished through the use of foil strain gages, which require surface preparation to install, and are unable to measure the distribution of dead load within the structure. The NDEVC is currently developing instrumentation and applications for the ultrasonic measurement of stress in bridge members.

The first method being developed involves the use of ultrasonic birefringence to evaluate the state of stress in a steel bridge member. A rotating transducer that launches polarized shear waves is used to measure magnitude of principle stresses. Applications of this technology for the evaluation of stress in hanger connection plates have been previously developed. Current studies are focused on evaluating the stress level in main members and lateral bracing systems.

Also being developed are methods for evaluating the stress level in high-strength steel strand used in pre-stressed and post-tensioned concrete applications. Strands are used in these applications to apply compressive loading in the tensile area of bridge beams, increasing the load carrying capacity of the member. Loss of pre-stressing force in these strands can reduce that load carrying capacity. The ultrasonic method being developed measures guided wave velocity to determine the force carried in the strands.

A nuclear instrumentation laboratory has been developed as part of the NDEVC. The laboratory is utilized for the evaluation and development of nuclear NDE techniques for highway applications. The nucleus of the laboratory is a state-of-the-art X-ray computed tomography (CT) system. The CT imaging system consists of dual focus 420 kV and microfocus 160 kV continuos X-ray sources. The system can benefit many industrial and scientific applications including materials research, non-destructive testing, core sample characterization, weld inspection and failure analysis.

Projects carried out at the laboratory have included the evaluation of available radiographic systems for the detection of broken wires in cable stayed bridges, imaging of post-tensioning strands in concrete beams, and the detection of voids in the grouted post-tensioning ducts.

Projects have also been conducted to evaluate the use of tomographic imaging for the evaluation of air entrainment and air-void distribution in concrete cores taken from highway bridges. Imaging of crack propagation in concrete cores caused by chemical attack has also been demonstrated.

Other project conducted in the laboratory include the design, fabrication, and evaluation of a portable system for nondestructive determination of chloride concentration in reinforced concrete structures, a system designed to identify areas susceptible to accelerated corrosion. Epithermal neutron detectors for non-destructive measurement of concrete hydration are also being developed to monitor concrete curing processes.

The development of new NDE technologies for the inspection of highways and highway bridges will assist the FHWA in attaining its stategic goals by helping to effectively manage the highway system in the twenty-first century. While many NDE tools are available or are being developed for highway application, few have been widely accepted for use in normal bridge inspections. The FHWA NDE Validation Center, through the development and evaluation of NDE technologies, will hopefully broaden the use of NDE and improve the state of the practice for highway bridge inspection.

This summary article is designed to provide a brief overview of activities at the center. For more information on the activities of the Center please contact us at:

Federal Highway Administration

NDE Validation center

6300 Georgetown Pike

McLean, VA 22101

Dr. Generazio presented an overview of NASA'S Agency-wide Nondestructive Evaluation (NDE) program, and reviewed the elements and status of the "Forever Young Vehicles" program that is being developed for Aerospace Vehicle Systems. The Forever Young Vehicles program is a "revolutionary" program that leverages off of NASA's prior and "proactive" Inherently Reliable Systems program. " The Inherently Reliable Systems program had followed the previous "reactive" Airframe Structural Integrity Program. The Forever Young Vehicles program has four thrust areas all focused toward the development of ageless vehicles. The four thrust areas within the Forever Young Vehicles program are damage science, central nervous systems, re-configurable and adaptable structures, and self-healing systems. NDE and sensors for vehicle central and peripheral nervous systems are major elements within NASA's NDE activities. NDE systems for damage assessment and control of structural reconfiguration and self-healing are also being pursued.

Most of the NDE activities at NIST are concentrated in the Materials Reliability Division of the Materials Science and Engineering Laboratory in Boulder, Colorado. Here the emphasis has been on materialcharacterization in which nondestructive measurements of certain physical properties are related to the microstructure of the material in order to infer the mechanical strength properties that are only measured by destructive tests. During the past few years, this approach has been applied to nuclear reactor pressure vessel steels that have been hardened by the formation of very small copper rich precipitates. Other programs have focused on development of new techniques to measure residual and applied stress in steel plates and to discover unique features in the acoustic emission signals produced by fatigue crack growth in bridge steels. Due to funding cuts by the agencies supporting these efforts and to the death or retirement of the key personnel, these programs have been curtailed and the emphasis has now shifted toward nondestructive evaluation of the materials and structures used in the microelectronics industry. The mechanism of failure in these microscopic structures are being examined by development of techniques to: (1) measure the stress-strain curves of aluminum and copper interconnect "wires" with micron dimensions; (2) display the thermal strain distribution patterns around solder ball connections in flip-chip package structures; (3) detect the formation of intermetallic phases at the copper-to-solder interface of printed circuit boards; and (4) examine the role played by the dislocation substructure in void formation by electromigration in damascene copper interconnects. In parallel with these failure mechanism studies, nondestructive materials characterization techniques are being developed to measure the ultrasonic properties of thin films on silicon single crystal substrates and to establish the sources of internal friction that determine the Q of resonator crystals intended to replace quartz in many clock and frequency standard applications.