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.

Rolling-contact fatigue (RCF) is a surface damage process due to the repeated application of stresses when the surfaces of two bodies roll on each other. This article briefly describes the various surface cracks caused by manufacturing processing faults or blunt impact loads on ceramic balls surfaces. It discusses the propagation of fatigue cracks involved in rolling contacts. The characteristics of various types of RCF test machines are summarized. The article concludes with a discussion on the various failure modes of silicon nitride in rolling contact. These include the spalling fatigue failure, the delamination failure, and the rolling-contact wear.

The properties of unidirectional composite (UDC) materials are quite different from those of conventional, metallic materials. This article provides information on the treatment of UDC stress-strain relations in the forms appropriate for analysis of thin plies of material. It explains the development of the relations between mid-surface strains and curvatures and membrane stress and moment resultants. The article discusses the properties, such as thermal expansion, moisture expansion, and conductivity, of symmetric laminates and unsymmetric laminates. It describes the distribution of temperature and moisture through the thickness of a laminate. Stresses caused due to mechanical loads, temperature, and moisture on the laminate are analyzed. The article concludes with information on interlaminar cracking, free-edge delamination, and transverse cracks of laminates.

Delamination is one of the most commonly observed failure modes in composite materials. This article describes the three fundamental fracture failure modes of composite delamination, namely, opening, in-plane shearing, and tearing or scissoring shearing modes. It discusses the characterization and analysis of delamination. The article also reviews the prediction of delamination factors, such as flexbeam fatigue life, and skin/stiffener pull-off strength and life.

In the design of composite structures for durability and damage tolerance, the primary concerns are out-of-plane failures, such as delamination, material degradation associated with environment, stability under compression loading, large degree of scatter in fatigue life, and bearing failure of joints. This article presents an introductory discussion on the fatigue damage process, methodologies assessing fatigue behavior, and life prediction models. It describes the damage mechanisms introduced for a quasi-isotropic laminate under tension-compression fatigue loading. Delamination is a critical issue in fatigue and generally results from high interlaminar normal and shear stresses. The article schematically illustrates the structural elements in which high interlaminar stresses are common. It concludes with a discussion on the classification of fatigue models such as mechanistic or phenomenological, for composite materials under cyclic loading.

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.

Knowledge of fatigue behavior at the laminate level is essential for understanding the fatigue life of a laminated composite structure. This article describes fatigue failure of composite laminates in terms of layer cracking, delamination, and fiber break and interface debonding. It discusses the fatigue behavior of composite laminates in the form of a relation between applied maximum fatigue stress and fatigue life. The article explains Weibull distribution and parameters estimation for fatigue data analysis and life prediction of composite laminates. It analyzes the fatigue properties and damage tolerance of fiber-metal laminates such as ARALL and GLARE laminates. The article concludes with a discussion on the effects of fatigue on notched and unnotched specimens.