What are "indications" in the context of ultrasonic testing?

In the context of ultrasonic testing, "indications" refer specifically to the signals or responses generated during the testing process that suggest the presence of a flaw within the material being examined. When ultrasonic waves are transmitted into a test object, they reflect off various material interfaces—these may include boundaries between different materials, inclusions, or any irregularities such as cracks and voids. The data received back, which are the echoes of these waves, serve as indications that help technicians identify and assess the nature of any flaws present.

Indications are critical in ultrasonic testing because they provide information that assists in evaluating the integrity of materials and components in a non-destructive manner. Proper interpretation of these signals enables an accurate assessment of the material's condition without causing damage.

Other options such as visual representations of internal structures, measurements of material properties, or errors during testing do not correctly encompass the definition of indications in this context. Each of those options relates to different aspects or processes of NDT but does not capture the essence of what indications are in ultrasonic testing.