From Metal Fatigue: What It Is, Why It Matters

C.1 Introduction

Non destructive testing (NDT) is not a clearly defined concept (Halmshaw 1991). NDT has a wide range of applications in the detection and evaluation of flaws in materials. Many different methods are used, and a wide range of commercially available instruments has been developed. These are often automated under computer control. The key feature of NDT is that it has no deleterious effect on the item tested.

In the context of metal fatigue the usual meaning of non destructive testing is the detection and sizing of cracks and crack like flaws in components, structures and laboratory specimens. This includes monitoring of fatigue crack propagation in service and in laboratory specimens; the advantages and disadvantages of various methods are summarised by Richards (1980). The accuracy of crack sizing that can be achieved varies widely.

Some of the non destructive testing techniques used in metal fatigue work are described briefly in this appendix, together with the important statistical concepts of probability of detection and probability of sizing. In order to make the appendix more self contained some figures in the main text are repeated here.

C.2 Visual Inspection

Visual inspection is the simplest method of detecting surface cracks, usually called surface breaking cracks in the non destructive testing literature. This term is used in this appendix. The utility and importance of visual inspection are often underestimated. Under good conditions fatigue cracks with a surface length of 3 mm can be detected by the naked...

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Nondestructive Testing (NDT) Equipment
Non-destructive testing (NDT) equipment is used to detect, inspect, and measure flaws, bond integrity, and other material conditions without permanently altering or destroying the examined part or product. NDT equipment includes a wide variety of instruments and systems.
Nondestructive Testing (NDT) Supplies and Accessories
NDT supplies and accessories are components, ancillary equipment, standards, and consumable materials used in non-destructive testing (NDT).
Nondestructive Testing (NDT) Material Testers
Non-destructive testing (NDT) material testers are devices, machines and equipment that are used to determine residual stress, alloy type, hardness, microstructure, elasticity, heat treatment and other material conditions without permanently altering or destroying the material being examined.
Flaw Detectors
Flaw detectors are used to detect or measure defects in raw materials or finished products. This product area includes fault detectors, NDT instruments that are used to find faults in electrical, mechanical, optical, or other systems.

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