Name at least three nondestructive evaluation techniques used for composites and what they detect.

• A. Ultrasonic C-scan (delamination/ interfaces); Thermography/IR (thermal anomalies); X-ray/CT (voids and porosity); Acoustic emission (damage events)
• B. Ultrasonic C-scan for color imaging; Thermography/IR for sound; X-ray/CT for surface roughness; Acoustic emission for magnetic fields
• C. Ultrasonic C-scan detects moisture only; Thermography detects color; X-ray detects fiber orientation; Acoustic emission measures stiffness
• D. Ultrasonic C-scan detects electrical conductivity; Thermography detects density; X-ray measures moisture; Acoustic emission detects color

Answer: (A)

Nondestructive evaluation methods for composites focus on “seeing inside” the material without cutting it open, each using a different physical signal to reveal hidden defects. Ultrasonic C-scan sends high-frequency sound into the laminate and builds a map of the interior, making delaminations and weak interfaces visible as variations in the image. Infrared thermography looks at how heat flows through the part; defects like delaminations or poor bonding disrupt heat transfer, so thermal patterns appear as anomalies on the surface or in a thermal image. X-ray or CT imaging uses penetrating radiation to view the internal structure in 2D or 3D, exposing voids, porosity, inclusions, or misaligned fibers that aren’t seen from the outside. Acoustic emission monitors the high-frequency elastic waves produced as the material experiences damage, providing real-time indications of crack initiation and growth or fiber breakage under load. The other statements don’t align with what these techniques actually detect—color imaging, surface roughness, moisture, magnetic fields, density, or electrical conductivity aren’t the primary measurements for these NDE methods in composites.