This paper provides an overview of methods to detect, locate, and characterize damage in structural and mechanical systems by examining changes in measured vibration response. Research in vibration-based damage identification has been rapidly expanding over the last few years. The basic idea behind this technology is that modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Therefore, changes in the physical properties will cause detectable changes in the modal properties. The motivation for the development of this technology is presented. The methods are categorized according to various criteria such as the level of damage detection provided, model-based vs. non-model-based methods and linear vs. nonlinear methods. The methods are also described in general terms including difficulties associated with their implementation and their fidelity. Past, current and future-planned applications of this technology to actual engineering systems are summarized. The paper concludes with a discussion of critical issues for future research in the area of vibration-based damage identification.

A powerful new method for residual stress measurement is presented. A part is cut in two, and the contour, or profile, of the resulting new surface is measured to determine the displacements caused by release of the residual stresses. Analytically, for example using a finite element model, the opposite of the measured contour is applied to the surface as a displacement boundary condition. By Bueckner’s superposition principle, this calculation gives the original residual stresses normal to the plane of the cut. This “contour method” is more powerful than other relaxation methods because it can determine an arbitrary cross-sectional area map of residual stress, yet more simple because the stresses can be determined directly from the data without a tedious inversion technique. The new method is verified with a numerical simulation, then experimentally validated on a steel beam with a known residual stress profile.

This article reviews the technical literature on the determination of a residual stress profile by successive extension of a slot and measurement of the resulting strains or displacements. This technique is known variously in the literature as the crack compliance method, the successive cracking method, the slotting method, and a fracture mechanics based approach. The article briefly summarizes the chronological development of this method and then, to facilitate more detailed review, defines the components that make up the method. The theory section of the article first considers forward method solutions including fracture mechanics, finite element, analytical, and body force methods. Then it examines inverse solutions, including incremental inverses and series expansions. Next, the article reviews all experimental applications of the crack compliance method. Aspects reviewed include the specimen geometry and material, the details of making the slot, the deformation measurement, and the theoretical solutions used to solve for stress. Finally, the article makes a brief qualitative comparison between crack compliance and other residual stress measurement methods. In many situations, the crack compliance method offers several advantages over other methods: improved resolution of residual stress variation with depth; the ability to measure both small and very large parts; measurement of stress intensity factor caused by residual stress; measurement of crack closure stresses; increased sensitivity over other material removal methods; and the ability to measure non-crystalline materials. This review article contains 77 references.