What is the boundary between two different materials in contact with each other called?

The term used to define the boundary between two different materials in contact with each other is an interface. In nondestructive testing, particularly in ultrasonic testing, the interface is crucial because it is at this boundary that significant changes in material properties occur, which can impact the propagation of ultrasonic waves. When ultrasounds encounter an interface, they may reflect, refract, or transmit depending on the material properties and the angle of incidence.

Understanding interfaces is vital for interpreting ultrasonic testing results, as they can reveal defects, variations in material density, and other critical factors that are essential for assessing the integrity of a material or structure. In practice, effective evaluation of interfaces helps in identifying issues such as voids, cracks, or other discontinuities that may compromise the material's performance. This concept is fundamental to ultrasonic testing techniques and is frequently referenced in NDT applications.