Nondestructive testing (NDT) or Nondestructive evaluation (NDE) is a method of materials testing to assess the characteristics of a component without altering or destroying it. NDT is important in the materials testing industry where quick, dependable information on finished or raw material is needed. This may occur during the production stage, during the service life of a material or product, or as a diagnostic tool in the event of material failure.
NDT is contrary to destructive testing such as stress or bend testing where critical material properties are determined through achieving specimen failure. While destructive testing is intrinsically more revealing; it also is costly to a manufacturing operation due to material loss and, for obvious reasons, it is not suitable for in service material testing.
Application uses for NDT cover a comprehensive range of material and industries such as automotive, aerospace, construction, and a multitude of manufacturing types. A classic example of NDT at work is testing for weld defects at manufacture and periodically during service life of the welded material. Other typical applications include crack detection in aircraft skins, surface flaws in pipes or bar, and evaluation of heat treating of product.
NDT has also become a valuable tool in the research and development field where quick, reliable data can provide vital information on materials. Typical types and method of NDT include Ultrasonics, Eddy Current, Rebound, and Ultrasonic Contact Impedance. Hardness testing by diamond or ball indentation is also, sometimes arguably, considered a form of NDT, as in most cases the material is only indiscernibly effected. The force applied in a hardness test correlated either with the depth of indent or with area of indent provides a measurement of hardness. Typically the properties and usefulness of the material is not compromised. Microhardness testing is the best example of a nondestructive hardness test. Some of the more common NDT test types are described below.
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