Final answer:
The correct option for TOFD testing is B: Low damping, small diameter, high frequency. This combination allows for a wider frequency range detection and a more focused beam, suitable for flaw detection in materials. Additionally, the loudest sound in a resonance experiment is produced when the vibration frequency matches the natural frequency of the air column.
Step-by-step explanation:
The TOFD (Time of Flight Diffraction) technique in ultrasonic testing uses a probe set up where both probes are positioned on opposite sides of the weldment. The correct option for carrying out TOFD among the given choices is option B: Low damping, small diameter, high frequency. This combination is used because low damping allows for a wider range of frequencies to be detected, which is crucial for identifying flaws within the material. A small diameter is generally preferred for the probes because it provides a more focused beam, which helps in detecting small flaws. High frequency ultrasound is primarily used for better resolution.
Regarding the resonance phenomena described, the air column will produce the loudest sound when the frequency of the vibration of the tuning fork is equal to the natural frequency of the air column, as stated in option option D.