Which ultrasonic testing methods allow the search unit to be in direct contact with the material being tested?

The correct answer is that all types of ultrasonic testing methods can allow the search unit to be in direct contact with the material being tested.

In ultrasonic testing (UT), the search unit, or transducer, emits ultrasonic waves into the material. When the transducer is in direct contact with the material, it ensures optimal coupling, which is crucial for the effective transmission of sound waves. Direct contact can be achieved using a couplant, such as gel or water, to fill any air gaps, thereby enhancing the efficiency of sound wave propagation.

Straight beam methods are typically used for thickness measurements and detecting flaws perpendicular to the beam path. Surface wave techniques can also rely on direct contact for evaluating surface or near-surface defects. Angle beam methods, which use ultrasound at oblique angles, can benefit from being in contact with the test piece to achieve proper beam alignment and penetration.

This flexibility allows ultrasonic testing to accommodate a variety of test scenarios and applications, making all types applicable when direct contact is required.