What are the most common causes for delamination of a composite structure?

• A. Sonic vibration, expansion of internal moisture, liquid leakage, and a manufacturing error.
• B. Exposure to ultraviolet light only.
• C. Overheating resin during cure.
• D. Impact damage not related to manufacturing.

Answer: (A)

Delamination happens when the bond between the layers of a composite fails and the plies separate under load. The most common culprits are factors that repeatedly stress or weaken those interlaminar bonds in service or during production.

Sonic vibration introduces cyclic interlaminar shear stresses that can crack the interfaces and propagate delamination under flight loads and engine/vibration environments. Internal moisture expansion causes the resin matrix to swell; this moisture-related swelling creates differential strains at the ply interfaces, promoting debonding and crack growth. Liquid leakage can carry chemicals that attack the adhesive or resin at the interfaces and can plasticize or weaken the matrix, reducing interlaminar strength and allowing layers to separate. Manufacturing errors, including voids, improper resin wet-out, misalignment, or incomplete curing, leave weak spots and residual stresses that predispose a laminate to delaminate when it experiences normal service loads or temperature changes.

Ultraviolet light mainly affects surface resin properties and is not a primary driver of through-thickness delamination in typical aerospace composites. Overheating resin during cure can cause curing defects and residual stresses, but it is not as common a root cause as moisture-related effects, vibroacoustic loading, liquid exposure, and manufacturing defects. Impact damage is a known cause, but the option describing multiple interrelated factors (vibration, moisture expansion, liquid leakage, and manufacturing error) best captures the most frequent ways delamination initiates and propagates.