For most nondestructive evaluation (NDE) applications, the term thermography actually refers to surface-excited thermography (SET) that involves thermal mapping of surface temperature as heat flows from, to, or through a test object in response to excitation applied to the sample surface. This article discusses the strategies for implementing thermography for NDE, including the steady-state/whole-body approach and transient heat conduction. It describes the most common signal-processing methods, such as thermographic signal reconstruction, lock-in thermography, and pulsed-phase thermography. The article concludes with a discussion on the use of thermal methods for thermal diffusivity measurement and characterization of multilayer structures.

Thermal nondestructive evaluation (TNDE) is an indirect process, so that regardless of the form of energy used to excite the sample, interaction with the internal structure of a part occurs through the process of heat conduction. This article discusses the steady-state configuration and selective excitation configuration of the signal-generation mechanisms in thermal nondestructive evaluation methods. The three widely used approaches to TNDE are surface-excited thermography, vibrothermography, and thermoelastic stress analysis. The article provides information on the common features, characteristics, and limitations of these approaches.

This article begins with an overview of the various aspects of infrared pulse thermography used to detect disbondments, delaminations, and generalized corrosion. It describes the distinctive phases of the pulse thermographic process and the key components that are required to perform active thermography. The components include an excitation source, a thermographic camera, and a computer with software that controls the instrumentation, acquires data, and displays the results. The article discusses the process and experimental setup of sonic thermography used for crack detection.

Vibrothermography, also known as sonic thermography, sonic infrared (IR), thermosonics, and vibroacoustic thermography, is a nondestructive evaluation (NDE) technique for finding cracks and delaminations through vibration-induced heating. This article describes the four parts of the vibrothermography process: vibration of the specimen by a transducer; conversion of vibrational energy into heat by a crack, delamination, and other contacting surfaces; conduction of the heat to an external surface; and infrared detection of the heat with a thermal camera.

Thermal inspection comprises all methods in which heat-sensing devices or substances are used to detect irregular temperatures. Inspection of workpieces can be used to detect flaws and undesirable distribution of heat during service. Though there are several methods of thermal inspection and many types of temperature-measuring devices and substances, this article focuses only on thermography, which is the mapping of isotherms, or contours of equal temperature, over a test surface, and on thermometry, which is the measurement of temperature. Thermography techniques can be classified as contact thermographic methods using cholesteric liquid crystals, thermally quenched phosphors, and heat-sensitive paints, and noncontact techniques using hand-held infrared scanners, high-resolution infrared imaging systems, and thermal wave interferometer systems. Contact thermometric inspection devices include bolometers, thermocouples, thermopiles, and meltable substances, whereas radiometers and pyrometers come under the noncontact category.

This article focuses on the methods that are being developed for detecting and monitoring corrosion: electrochemical methods, electromagnetic or sound wave methods, fiber-optic technology, fluorescence methods, and the Diffracto Sight method. It reviews the importance of data management and the Corrosion Expert System. It concludes with information on the simulation and modeling for incorporating the mechanisms of corrosion prevention into military hardware systems design and operation.

The goal of using nondestructive evaluation (NDE) in conjunction with failure analysis is to obtain the most comprehensive set of data in order to characterize the details of the damage and determine the factors that allowed the damage to occur. The NDE results can be used to determine optimal areas upon which to focus for sectioning and metallography in order to further investigate the condition of the component. This article provides information on the inspection method available for failure analysis, including standard methods such as visual testing, penetrant testing, and magnetic particle testing. It covers the effects of various factors on the properties of the part that may impact failure analysis, describes the characterization of damage modes and crack sizes, and finally discusses the processes involved in application of NDE results to failure analysis.

This article introduces the principal methodologies and some advanced technologies that are being applied for nondestructive evaluation (NDE) of fiber-reinforced polymer-matrix composites. These include acoustic emission, ultrasonic, eddy-current, computed tomography, electromagnetic acoustic transducer, radiography, thermography, and low-frequency vibration methods. The article also provides information on NDE methods commonly used for metal-matrix composites.

This article introduces the principal methodologies and some technologies that are being applied for nondestructive evaluation of composite materials. These include ultrasonic testing (UT), air-coupled UT, laser UT, ultrasonic spectroscopy, leaky lamb wave method, acousto-ultrasonics, radiography, X-ray computed tomography, thermography, low-frequency vibration methods, acoustic emission, eddy current testing, optical holography, and shearography. The article presents some examples are for fiber-reinforced polymer-matrix composites. Many of the techniques have general applicability to other types of composites such as metal-matrix composites and ceramic-matrix composites.

This article provides a discussion on general nondestructive evaluation (NDE) science and considerations for specific technique selection. It explains the basic concept of flaw detection and evaluation and probability of detection. The article provides an overview of NDE methods with their applications, limitations, and advantages. It includes details on NDE codes, calibration standards, inspection frequency, guidance on how to perform inspections, applicability, and mandatory and nonmandatory practice. The article also provides tips on where to focus inspections in order to align with the likely areas of damage or degradation and a number of other aspects of inspection.

Thermoelastic stress analysis (TSA) an increasingly popular infrared (IR)-based technique for measuring stress on the surface of a part subjected to time-varying loads. This article begins by providing a theoretical and historical background of thermoelastic stress analysis. It then describes infrared detectors, such as quantum detectors and thermal/nonquantum detectors, for thermoelastic stress analysis. The article discusses the theoretical aspects for producing thermoelastic stress analysis data and the applications amenable to thermoelastic stress analysis. It concludes with information on the qualitative applications of thermoelastic stress analysis.

The formation of defects within additive-manufactured (AM) components is a major concern for critical structural and cyclic load applications. Thus, understanding the mechanisms of defect formation in fusion-based processes is important for prescribing the appropriate process parameters specific to the alloy system and selected processing technique. This article discusses the formation of defects within metal additive manufacturing, namely fusion-based processes and solid-state/sintering processes. Defects observed in fusion-based processes include lack of fusion, keyhole collapse, gas porosity, solidification cracking, solid-state cracking, and surface-connected porosity. The types of defects in solid-state/sintering processes are sintering porosity and improper binder burnout. The article also discusses defect-mitigation strategies, such as postprocess machining, surface treatment, and postprocessing HIP to eliminate defects detrimental to properties from the as-built condition. The use of noncontact thermal, optical, and ultrasound techniques for inspecting AM components are also considered. The final section summarizes the knowledge gap in our understanding of the defects observed within AM components.

This article focuses on the aspects associated with inspection related to pressure vessels and pipework. These aspects include inspection policy, inspection planning and procedures, inspection strategy, inspection methodology, preparation for inspection, invasive inspection, internal visual inspection, and non-invasive inspection. Inspection execution, risk-based inspection, competence assurance of inspection personnel, inspection coverage, inspection periodicity, inspection anomaly criteria, assessment of fitness, and reporting requirements, are also discussed. The article addresses the data acquisition, reporting and trending, and review and audit for the inspection. It reviews inspection techniques, including visual inspection, ultrasonic inspection, and radiographic inspection.

This article provides information on the application of nondestructive examination (NDE) technologies to tube and pipe products. These include modeling and simulation methods, eddy-current methods, magnetic methods, acoustic methods, and physical methods. A summary of nondestructive examination methods based on flaw type and product stage is presented in a table. The article also discusses in-service inspection of tubular products and presents an example that illustrates the importance of nondestructive testing (NDT) for welds in austenitic stainless steel tubing.

Fusion welding processes involve four phase changes, namely, solid-solid state, solid-liquid, liquid-vapor, and vapor-plasma. Each has its own thermal, momentum, and stress history. This article discusses some important techniques to validate temperature, momentum, stress, and residual strain history observed in the heat-affected zone of fusion welded materials.

The potential for introducing defects during processing becomes greater as the relative density of pressed and sintered powder metallurgy (PM) parts increases and more multilevel parts with complex geometric shapes are produced. This article discusses the potential defects in pressed and sintered PM parts: density variations, compaction and ejection cracks, microlaminations, poor degree of sintering, and voids from prior lubricant agglomerates. It describes the various methods applicable to green compacts: direct-current resistivity testing, radiographic techniques, computed tomography, and gamma-ray density determination. The article also discusses the methods for automated nondestructive testing of pressed and sintered PM parts: acoustic methods-resonance testing, eddy current testing, magnetic bridge comparator testing, ultrasonic techniques, radiographic techniques, gamma-ray density determination, and visual inspection.

This article provides an overview of the methods used to control aspects of the arc welding process and research associated with the development of closed-loop feedback control of the process. Successful implementation of a closed-loop feedback control system requires sensing, modeling, and control. The article describes the commonly applied sensing techniques for arc welding control: arc sensing and nonimaging and imaging optics. It reviews the physics-based, empirically-derived, and neural network models for arc welding control. The article also discusses the research and development activities that attempt to extend the commercial, welding process controllers, namely, adaptive control, intelligent control, multivariable control, and distributed, hierarchical control.

Nondestructive testing (NDT), also known as nondestructive evaluation (NDE), includes various techniques to characterize materials without damage. This article focuses on the typical NDE techniques that may be considered when conducting a failure investigation. The article begins with discussion about the concept of the probability of detection (POD), on which the statistical reliability of crack detection is based. The coverage includes the various methods of surface inspection, including visual-examination tools, scanning technology in dimensional metrology, and the common methods of detecting surface discontinuities by magnetic-particle inspection, liquid penetrant inspection, and eddy-current testing. The major NDE methods for internal (volumetric) inspection in failure analysis also are described.

The influence of friction and wear on the function and structure of tribological systems is determined by various types of tribological tests. This article introduces the general categories of tribological testing and describes the basic objectives of testing. It reviews the results of tribological tests, where the system-dependent characteristics of friction and wear data can be expressed in different forms, such as tribographs, transition diagrams, and tribomaps. A summary of various methods of surface analysis is presented in a table. The article discusses the relationship between wear and reliability in terms of exponential distribution, Weibull distribution, and gamma distribution. It concludes with information on the effects of interaction on failure probability.