This paper describes the results of the comparison of a variety of nondestructive evaluation techniques to monitor the development of fatigue damage in thick graphite/epoxy composites. Three inch long, one inch square cross-section test specimens were fatigue tested in compression. Most specimens incorporated stress (strain) concentration notches at their mid- section in order to localize the primary fatigue damage regions in an optimum location for nondestructive monitoring. The nondestructive techniques evaluated were ultrasonic B- and C- scan, ultrasonic velocity and attenuation, ultrasonic second harmonic generation, acoustic microscopy, acoustic emission, thermography, real-time high-speed digital/video laser speckle decorrelation, magnetic resonance imaging, radio-opaque penetrant enhanced x-radiography, and eddy current. Mechanical resonance spectroscopy was used to measure the second order (linear) elastic moduli. Optical and electron microscopy on cut and polished specimens were used to verify the results of the nondestructive tests.

Glass fiber composite materials have been used for many years in the construction of pleasure, cruising, and racing marine vessels. These vessels have demonstrated excellent performance characteristics and have been reliable in service. Even so, as with all material systems, they are subject to damage from accident, neglect, and abuse. Traditional nondestructive inspection approaches are not always fully effective for examining composite marine structures. Infrared imaging offers a particularly attractive approach for the inspection of composite material structures. Glass fiber composites frequently possess a combination of thermal properties that make them good candidates for infrared thermographic evaluation while other nondestructive evaluation approaches provide limited success. Infrared thermography combines the advantages of being nondestructive with the capability of rapidly inspecting wide surface areas.

Composite materials, which have commonly been used in recreational boats, are now being applied to more challenging marine applications. The high specific stiffness and strength of composites translates into increased range and payload. Composites offer the added benefits of corrosion and erosion resistance, fatigue and wear resistance, reduced signature, and reduced maintenance and life cycle costs as compared to traditional metallic structures. Although ultrasonic techniques are typically used to inspect composite structures, thick composites, such as those used in marine applications, are difficult to inspect with ordinary ultrasonic methods. An ultrasonic inspection system is being developed for the US Army to inspect thick composite materials for future armored vehicles. This system is an extension of the existing PARIS flexible array ultrasonic inspection system, which was originally developed for inspecting thin composite aircraft structures. The extension is designed to increase ultrasonic penetration by 1) fabricating an array that operates at lower frequency and higher voltage, and 2) employing a synthetic pulse technique. The flexible array can rapidly inspect large areas and produce images of the inspection results that are easy to interpret. This paper describes the ultrasonic inspection system and presents examples of inspection results from both thick and thin composite materials.

Glass fiber reinforced polymer composites are being considered by the US Navy for top-side structures on ships. Electronic equipment and personnel inside these structures must be protected from electromagnetic interference and radiation hazards from friendly and hostile sources. Since these composites are nondesctructive, metallic layers of various architectures, composition, and lay-ups have been incorporated into them for electromagnetic shielding. This paper will present electromagnetic NDE data on some of these metal-clad, nonconductive composites. Low frequency eddy-current test results will be compared to the electromagnetic shielding performance at microwave frequencies. Issues associated with corrosion will be discussed.

Because of its ability to provide radiographic information from one side of a structure, x-ray backscatter tomography (XBT) offers great promise for NDE where other methods are thwarted by object size or inaccessibility. For several years NRL has been using a Philips ComScan semiportable XBT unit to develop an underwater NDE system for Navy sonar domes on surface vessels. Along the way we have had opportunities to apply this new technology to samples of a number of other materials. We will describe progress toward our dome inspection system and results from other materials.

The convergence of a number of contemporary technologies with increasing demands for improvements in inspection capabilities in maritime applications has created new opportunities for ultrasonic inspection. An automated ultrasonic inspection and data collection system APHIUS (automated pressure hull intelligent ultrasonic system), incorporates hardware and software developments to meet specific requirements for the maritime vessels, in particular, submarines in the Canadian Navy. Housed within a hardened portable computer chassis, instrumentation for digital ultrasonic data acquisition and transducer position measurement provide new capabilities that meet more demanding requirements for inspection of the aging submarine fleet. Digital data acquisition enables a number of new important capabilites including archiving of the complete inspection session, interpretation assistance through imaging, and automated interpretation using artificial intelligence methods. With this new reliable inspection system, in conjunction with a complementary study of the significance of real defect type and location, comprehensive new criteria can be generated which will eliminate unnecessary defect removal. As a consequence, cost savings will be realized through shortened submarine refit schedules.

This paper describes a US Navy project to replace its current recertification requirement of removing high-pressure flasks from the ship to perform a hydrostatic test with a new test requirement to perform an in-situ acoustic emission inspection.

As with any metal structure, fatigue and corrosion of oil platforms are major concerns that require constant surveillance. Visual inspections can be carried out underwater effectively by divers, but more sophisticated nondestructive test (NDT) methods are sometimes necessary. This paper will trace the development of equipment from simple encapsulated versions of land-used instruments where the main question was whether to train NDT operators as divers or vice versa, to the modern systems operated from remote operated vehicles. Some of the interesting innovations along the way, such as torch-like ultrasonic thickness gauges, and devices for detecting flooded members will be described.

Carderock Division, Naval Surface Warfare Center, Code 623 has been involved in the nondestructive test and evaluation of US Navy surface vessels since the 1960s. In this time, CDNSWC 623 has been involved in the utilization and technical development of many forms of NDE including visual inspection, contact ultrasonics, eddy current inspections, computer- automated ultrasonics, and laser optics. The present laser optic tube inspection system (LOTIS) was developed through a joint venture between NSWCCD 623 and Quest Integrated, Inc. of Kent, WA. CDNSWC 623 is presently involved in the centralization of several fleet- wide NDE practices including boiler inspection devices, contact ultrasonics, eddy current, the ultrasonic tube inspection system, and the LOTIS. These systems all have very diverse ranges of application and have proven to be cost-saving devices when implemented throughout the US Navy.

Detection of hidden corrosion on aircraft structures using conventional ultrasonic testing (UT) techniques is difficult because of the thin walls and topography of the corrosion. These characteristics require use of high-frequency, high-spatial-resolution transducers to attempt to detect backwall signal amplitude. It is usually difficult to visually discriminate backwall signals of thin wing structure from the normal ringdown of the initial pulse of the transducer (from the front-surface reflection). A technique was developed that increases the reliability of ultrasonic detection of hidden corrosion. The technique, called aural ultrasonics, involves complete transformation of the ultrasonic information into audible sounds. A trained inspector can listen to the sounds generated by the aural UT equipment and detect the presence of hidden corrosion. The aural ultrasonic technique, associated equipment, and evaluation on hidden-corrosion test samples will be discussed in this paper.

A technique for inspecting steel pipes or tubes using magnetostrictive sensors (MsSs) is described. Signals acquired from approximately 6.6-m-long, 164-mm-diameter, 5-mm-wall steel pipes before and after inducing a simulated corrosion defect are given. The data show that the MsS technique is very sensitive to corrosion-type defects and can be used for 100% volumetric inspection of a long segment of piping from a single sensor location. Also, the ability to operate the sensor with a substantial gap to the outside surface of pipe makes the MsS technique suitable for inspection of piping under thermal insulation or lagging.

The interior of the housings of primary and backup shaft seals of 637 class submarines are exposed to sea water during service and become corroded during service. Corrosion damage evaluation requires disassembly of the housing and visual inspection. In this paper, we present quantitative results of in situ nondestructive ultrasonic technique developed for the inspection of the seal housings. Due to vast variations in velocity in the seal material, the velocity was determined at suitable sites not subjected to corrosion and of known thickness from the blueprints. Using this normalized velocity and measured time-of-flight, we determined the thickness of the seal housing at various locations on the circumference. Subsequent mechanical thickness measurements, made when the housings were removed from service, agreed within the predicted uncertainty of 1.5% of ultrasonic measurements. This technique for the assessment of corrosion damage saves time and money, by preventing premature disassembly and downtime for the submarine.

Good adhesive bond between the laminates is extremely important for the shear strength of adhesively bonded poly-rubber-steel concetric cylinders used as marine shaft vibration reducers (SVR). The SVR are inspected nondestructively by using a high-speed PC-based transmission ultrasonic C-scan system capable of scanning and producing images. Transmission of ultrasound at frequencies between 5-20 MHz and time-of-flight variations of these signals through these multilayered structures is used to determine the disbonds at the interfaces. Two- and three-dimensional images are generated and analyzed statistically to quantify the areas of disbond. Mathematical models for the propagation of ultrasound through such a layered structure are applied for the interpretation of these images.

Effective 'hull condition assessment' relies not only on regular, intensive ultrasonic inspection but also on proper analysis of the collected data. Practical appraisal can only be achieved by computerization--a task hindered by the lack of standards. Historically, engineering terms, gauging patterns, equipment standards, definitions, and nomenclature have varied from one classification, society, shipowner, shipbuilder, and NDT Company to another. The International Association of Classification Socieities should be formalizing standards; they appear to be causing more fragmentation. Surtest Marine and Cygnus Instruments are forming systems that they feel must meet the necessary criteria for all parties in today's technologically and financialy demanding shipping industry.

I am pleased to welcome you to this timely and informative conference organized by The International Society for Optical Engineering (SPIE). As Conference Chair, I am very pleased, but not at all surprised, by your interest and enthusiastic response: Over 300 participants are contributing over 210 technical papers to six topical conferences.

The infrastructure in the United States and the world is aging. There is an increasing awareness o the need to assess the severity of the damage occurring to our infrastructure. Limited resources preclude the replacement of all structures that need repairs or have exceeded their lifetimes. Methods to assess the amount and severity of damage are crucial to implementing a systematic, cost effective approach to repair and/or replace the damaged structures. The challenges of inspecting aging structures without impairing their usefulness rely on a variety of technologies and techniques for nondestructive evaluation. This paper will briefly describe several nondestructive evaluation technologies that re required for inspecting a variety of systems and structures.

the role of the National Laboratory in technology transfer is to help industry implement the latest technology. The National laboratory must have a unique capability that does not compete with tax paying companies. Typically a National Laboratory will demonstrate the benefit of applying NDE to a company's production line. The company then contracts with a vendor to supply a production inspection system based on the laboratory's demonstration. Both the company and the vendor benefit from the participation with the National Laboratory. The company improves the quality of its products and the vendor has a new product to market. The purpose of this paper is twofold: (1) to present a brief overview of NDE capabilities and application activities within the National Laboratory System and (2) to identify NDE point-of- contacts at each laboratory.

Quasistatic spatial mode (QSM) sensing is a new form of nondestructive evaluation developed to address the increasing need for quantitative materials characterization. Two types of QSM sensors and measurement methods are described: QSM magnetometry and QSM dielectrometry. These measurement methods were invented at the MIT Laboratory for Electromagnetic and Electronic Systems and are being developed at JENTEK Sensors, Inc. for specific applications, such as coating porosity characterization. The sensors discussed here are the meandering winding magnetometer and the inter-digital electrode dielectrometer. These sensors are thin and flexible, permitting inspection of complex and difficult-to-access surfaces. Using continuum electromagnetic models of the sensor field interactions with multiple layered media, repeatable and quantitative measurement of physical and geometric properties are obtained. The specific application addressed here is the characterization of coating and component condition for turbine blades. This includes measurement of thickness and porosity for both ceramic and metallic coatings. Future research will focus on age degradation monitoring as well.