Which NDT method should not be used to detect cracks in advanced composite structures?

The use of dye penetrant testing (PT) in detecting cracks in advanced composite structures is not suitable because this method relies on the penetration of a liquid dye into surface-breaking defects. While effective for metallic surfaces, advanced composites can be porous or have a layered structure that limits the effectiveness of dye penetrants. Additionally, the chemicals in the dye may adversely affect the composite material, potentially causing damage or contamination.

In contrast, ultrasonic testing (UT) is a non-destructive method well-suited for advanced composites because it utilizes high-frequency sound waves to detect internal flaws, such as voids or delaminations, without relying on surface characteristics. Magnetic particle testing, on the other hand, is specifically for ferromagnetic materials and requires the presence of magnetic properties to identify defects, making it irrelevant for composites.

Thus, the choice of dye penetrant testing as unsuitable for advanced composites accurately reflects its limitations in this context.