Subsonic vs. Supersonic Fatigue

[lLouie]

• Subsonic Flight: Fatigue is primarily dominated by high-cycle fatigue (HCF) due to repetitive low-stress loading. The absence of extreme thermal fluctuations reduces the impact of thermal fatigue, leading to a longer material lifespan.
• Supersonic Flight: More severe low-cycle fatigue (LCF) occurs due to rapid pressure fluctuations from shock waves. Additionally, aerodynamic heating causes thermal fatigue and creep, accelerating material degradation. Therefore, high-temperature-resistant materials like titanium alloys and composite materials are crucial for durability.

​

I came across AGARD while researching. The fatigue behavior will be different between subsonic and supersonic flight. So, what kind of aerodynamic loading will occur when transitioning from subsonic to supersonic? For fatigue analysis, both subsonic and supersonic conditions need to be considered.

I am curious about your opinion on this and whether there are any relevant sources available. Could you share any references on this topic?

 

[rb1957]

Maybe Concorde testing ? Thermal effects are significant, at least for metallic structures.

Maybe this is like fuselages (pressure vessels) one really large cycle per flight and lots of (almost) insignificant) little ones ?

 

[lLouie]

Yes, are thermal effects significant for both cases, or when going from subsonic to supersonic?
I'm looking at the metal parts which are in the wings.

 

[rb1957]

I think the thermal effects are apparent during supersonic flight, not just in the initiation of supersonic flight (breaking the sound barrier).

But I think there is excess loads when going supersonic.

 

[lLouie]

I think the thermal effects are apparent during supersonic flight, not just in the initiation of supersonic flight (breaking the sound barrier).

But I think there is excess loads when going supersonic.

Yes, you are right.
As the aircraft accelerates, the temperature will also increase. Therefore, the g loads on the wing will also be very different.
As a result, it is necessary to examine both situations separately in detail.

 

[rb1957]

as the plane flies supersonic, it'll heat soak until it reaches a stable temperature.

"Therefore, the g loads on the wing will also be very different." ... well, aerodynamic loads, though sure, the plane is accelerating (but not manoeuvreing).