This article provides readers with a brief review of the applications of thermography in additive manufacturing (AM), which still is largely a research and development (R&D) effort. There is a particular focus on metals-based laser powder-bed fusion (L-PBF), although applications in directed-energy deposition (DED) and electron beam PBF (E-PBF) also are mentioned. The metrological basis of thermography is discussed in the article. Background information on radiation thermometry is provided, including how the various equations are applied. Finally, specific examples and lessons learned from various AM thermographic studies at the National Institute of Standards and Technology (NIST) are provided.

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.

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 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.

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 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 introduces the concept of condition monitoring (CM) and summarizes various techniques used for CM across the industrial sectors. The techniques include visual inspection, performance monitoring, vibration condition monitoring, vibration condition monitoring, lubricant oil analysis, acoustic emission testing, temperature monitoring, motor current signature analysis, and ultrasound emission. The article describes the evolution of condition-based maintenance in CM. It also describes the basics of integrated vehicle health management, a capability that enables a number of maintenance philosophies. The article concludes with a discussion on various condition monitoring in industrial sectors, including condition-monitoring techniques in nuclear power plants, road condition monitoring, and condition monitoring in wind turbines.

Mechanical and environmental loadings cause a variety of failure modes in composites, including matrix cracking, fiber-matrix debonding, delamination between plies, and fiber breakage. This article summarizes visual analysis and nondestructive testing methods for the failure analysis of composites. These methods include radiography, ultrasonic techniques, acoustic emission, and thermograph. The article also provides information on destructive test techniques.

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.

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.

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.