Civil structures (such as bridges and buildings) and mechanical parts (for cars, planes, trains, etc.) exist to solve problems and simplify life. The final part must be functional, safe, reliable, competitive, usable, manufacturable, and marketable.
As explained throughout the book, designed components are exposed to specified and unspecified loads. The main task of the design team is to develop the component to mechanically withstand this set of loads during the service life. Nevertheless, unpredictable loads, external agents (generating corrosion), and known service loads produce fatigue or wear and necessitate inspection to ensure the integrity and safe functioning of the component.
Visual inspection was the first way to evaluate health integrity of a mechanical or civil structure, and it remains an important, valuable, and widely used nondestructive method to assess discontinuities exposed to the surface of the material. Advances in optics, digital image storage, and digital image processing have expanded the applications of visual inspection. In this case, optical methods can be considered as an extension of this technique because they are used to “monitor” the surface of a material under test and to identify possible anomalies not only on the surface but also below it.
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