Which of the following is NOT a common cause of delamination in composite structures?

Excessive heat is a factor that can indeed impact composite structures, leading to degradation of materials and potential delamination, but it is not considered a common cause of delamination. In composite structures, high temperatures can weaken the bond between layers, but they generally need to be extreme or sustained over time to cause significant damage. The more common causes of delamination typically involve mechanical stresses, environmental factors, or interruptions in the manufacturing process.

Conversely, sonic vibration, liquid leakage, and manufacturing errors are well-documented contributors to delamination. Sonic vibrations can create stresses that may lead to layer separation, especially in composite materials that can be sensitive to repetitive mechanical cyclic loading. Liquid leakage, such as moisture intrusion or fluid contamination, can lead to chemical reactions or weakening of the materials, causing them to delaminate over time. Manufacturing errors, such as improper curing or insufficient resin, can also lead to weak points in the structure that are susceptible to separation.

Thus, while heat can have adverse effects, it is not the primary contributor to delamination compared to the other listed factors.