Which type of ultrasonic testing involves the search unit being in direct contact with the material being tested?

The correct answer is that all types of ultrasonic testing can involve the search unit being in direct contact with the material being tested. Each testing method can be adapted to use a contact technique, depending on the specific application and inspection requirements.

In straight beam testing, the transducer emits sound waves directly into the material, and having the search unit in contact ensures efficient energy transfer and better sensitivity to detect flaws. Surface wave testing, while generally related to surface inspections, can also utilize contact methods to investigate near-surface or surface-borne discontinuities effectively. Angle beam testing relies on the angles of transmission to detect discontinuities at various depths, and this technique can be performed with the search unit in contact with the material to ensure proper alignment and optimal performance.

The ability to utilize contact methods across these different types of ultrasonic testing enhances the versatility and effectiveness of NDT techniques, allowing for tailored approaches based on the characteristics of the material and the nature of the flaws being inspected.