This article describes the test techniques that are available for monitoring crack initiation and crack growth and for obtaining information on fatigue damage in test specimens. These techniques include optical methods, the compliance method, electric potential measurement, and gel electrode imaging methods. The article discusses the magnetic techniques that are primarily used as inspection techniques for detecting fatigue cracks in structural components. It details the principles and operation procedures of the liquid penetrant methods, positron annihilation techniques, acoustic emission techniques, ultrasonic methods, eddy current techniques, infrared techniques, exoelectron methods, and gamma radiography. The article explains the microscopy methods used to determine fatigue crack initiation and propagation. These include electron microscopy, scanning tunneling microscopy, atomic force microscopy, and scanning acoustic microscopy. The article also reviews the X-ray diffraction technique used for determining the compositional changes, strain changes, and residual stress evaluation during the fatigue process.

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.

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.

A cylindrical specimen compressed with friction at the die surfaces does not remain cylindrical in shape but becomes bulged or barreled. Tensile stresses associated with the bulging surface make the upset test a candidate for workability testing. This article discusses test-specimen geometry and friction conditions; strain measurements; crack detection; and material inhomogeneities, which are to be considered for performing cold upset testing. It describes test characteristics in terms of deformation, free-surface strains, and stress states for performing cylindrical compression tests. The article illustrates the fracture loci in cylindrical, tapered, and flanged upset-test specimens of aluminum alloy and type 1045 cold-finished steel.

Fracture control is a systematic process to prevent fracture during operation that depends on the criticality of the component, the economic consequences of the structures being out of service, and the damage that would be caused by a fracture failure. This article describes the key principles of fracture control and reviews the concepts of damage tolerance analysis. It further presents practical guidelines to obtain useful and reasonable answers from damage tolerance analysis. The article concludes with information on fracture mechanics and fatigue design.

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.