The accumulation of particles at a site on the surface of a part due to a magnetic leakage field is known as what?

The term for the accumulation of magnetic particles at a site on the surface of a part due to a magnetic leakage field is referred to as an "indication." This phenomenon occurs during magnetic particle testing, where the presence of a magnetic field creates areas of leakage at discontinuities (such as cracks or voids) found within the material being inspected.

When magnetic particles are applied to the surface, they will congregate at these leakage fields, forming a visible pattern that indicates the presence of a defect. The indication itself is not the defect but rather a signal that shows where a potential issue may reside. This distinction is important in non-destructive testing, as it helps inspectors identify and evaluate the integrity of parts without causing damage.

In summary, "indication" is the term used to describe the visual manifestation of magnetic particles clustering in response to a magnetic leakage field, making it the correct answer to this question.