Study of fatigue crack characteristics by acoustic emission

Different critical load determination techniques such as microscopy, acoustic emission, normal, tangential, and lateral forces used for scratch test evaluation of complex or multilayer coatings are investigated. The applicability of the scratch test to newly developed coating techniques, systems, and applications is discussed. Among the methods based on the use of a physical measurement, acoustic emission detection is the most effective. The dynamics ratio between the signals below and above the critical load for the acoustic emission (much greater than 100) is well above that obtained with the normal, tangential, and lateral forces. The present commercial instruments are limited in load application performance. A scratch tester able to apply accurate loads as low as 0.01 N would probably overcome most of the actual limitations and would be expected to extend the scratch testing technique to different application fields such as optics and microelectronics.

The scratch test - Different critical load determination techniques

Abstract Different techniques for determining the critical load of coated products (microscopy, acoustic emission, and normal, tangential and lateral forces) are presented; the suitability of each is discussed. It appears that the most straightforward technique is microscopic observation. Among the methods based on the use of a physical measurement, acoustic emission detection is the most effective. The dynamics ratio between the signals below and above the critical load for the acoustic emission (much greater than 100) is well above that obtained with the normal, tangential and lateral forces (from less than 5 to 10). Finally, the fields of application of the scratch test as an adhesion test are discussed.

The scratch test - Different critical load determination techniques. [adhesive strength of thin hard coatings

The use of ultrasonic waves in nondestructive evaluation is reviewed. Perspective is provided by a summary of the role played by nondestructive evaluation in the manufacture and utilization of structural components. Included are discussions of the methodologies for predicting part serviceability and of the constraints placed on the nondestructive measurement process by the mechanical designs and functions of structural components. The principles of active (ultrasonic) and passive (acoustic-emission) testing techniques are then reviewed. Specific examples of applications from several industries illustrate the capabilities and limitations of state-of-the-art techniques based on these principles. Detailed discussion is then given of present research and development activities designed to overcome these limitations, with particular emphasis on those areas best addressed by the tools of electrical engineering. Included are discussions of instrumentation, inspection performance modeling, flaw sizing techniques (including imaging systems), material property measurement techniques, and acousticemission techniques. The paper concludes with a consideration of important directions of future work.

Ultrasonics in nondestructive evaluation

Investigation of pitting corrosion of stainless steel by means of acoustic emission and potentiodynamic methods

Acoustic-emission techniques are beginning to be frequently used as a means of detecting and locating deformation and fracture processes in both metallic and non-metallic engineering structures This has happened despite a relatively poor understanding of the basic physical processes involved in the generation, propagation, and detection of acoustic-emission signals, and of the influence in metals of factors such as composition and microstructure, upon the acoustic emission from different types of deformation and fracture processes The measurement of acoustic emission, potentially, could yield much information about dynamic aspects of these processes However, it is shown that the limitations of existing acoustic-emission recording instrumentation have enabled only qualitative information to be obtained to date Even this data, however, has demonstrated that metallurgical variables greatly affect the acousticemission response of metals, and simple models to account for this are discussed

C. B. Scruby

Papers

Acoustic emission for physical examination of metals