What material property changes might indicate thermal damage?

The correct choice highlights that alterations in tensile strength can indicate thermal damage to materials used in aircraft structures. When metals or composites are exposed to high temperatures, several changes in their microstructure may occur, which can affect their mechanical properties.

For example, excessive heat can lead to grain growth in metals, altering their tensile strength either by increasing it due to changes in crystalline structure or decreasing it due to softening or phase changes. Monitoring tensile strength is crucial in structural integrity assessments, as a decrease in this property can result in a failure mode that does not manifest until the structure is under actual service loads.

In contrast, the other material properties listed do not typically correlate with thermal damage in the same direct manner. Increased flexibility, enhanced fatigue resistance, and improved corrosion resistance may not occur as a direct consequence of thermal exposure, and in fact, may be incorrect assumptions about how materials respond to such conditions. Hence, focusing on alterations in tensile strength provides a clear indication of possible thermal damage.