8. 49 4. Magnetic Anomaly --ferromagnetic materials only --moderate depth penetration (otherwise similar to ultrasonics) 5. Acoustic Emission (8.18), (8.19), (8.20), (8.21) --extremely sensitive --wide area (or volume) coverage --instantaneous response --scanning unnecessary, but also impossible --responds to dynamic stresses only --poor measurement of flaw size and location --little current industrial use--no data base 6. Eddy Current --extremely sensitive to surface flaws --easily automated --shallow penetration ~-small search area per transducer --ferromagnetic materials degrade performace These are the only really practical NDE methods for use on the space colony prototype. Many techniques simply do not work in a zero-gravity vacuum environment (e.g., liquid penetrants), or are much too awkward to use on large scale construction in space (e.g., holography) . Radiography can almost be eliminated because of its low accuracy and two-sided access requirement, and should be avoided if at all possible because of the radiation hazard. The relative crudity of visual/optical inspection limits it to last-resort checking for major damage. Acoustic emission has much promise, but its practical reliability is hard to predict, and additional inspection is usually required. Eddy current techniques are limited to very thin materials. and do not have the operational flexibility of ultrasonic or magnetic anomaly methods. This leaves ultrasonics and magnetic anomaly as the preferred techniques. Ultrasonics has the additoinal advantage that it can give direct dimensional measurements, so it has been chosen as the primary inspection method. (The proposed electromagnetic ultrasonic probes are also sensitive to magnetic anomalies.) Ultrasonic methods have also been well proven in industry.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==