The quality of steel in war production no4s

[jmoore]

1. Only steel is considered to have an infinite life (if the iron moths stay away). I was told Aluminum has an effecive life of 40 years. Memo to those who gad about in WWII period airplanes. Interestingly, I was never exposed to how to work this information into calculations or factors of safety or how the failure mode would develop.

I've not seen any documentation on intergranular growth in steels yet, plenty on "fatigue", which often looks like some sort of embrittlement. Would enjoy seeing studies, though, if y'all could link some. ASME, SAE, ASTM, etc. or other countries' equivalents.

As for the degradation of aluminum alloys, it must be an environmental thing. The usual mechanism being "intergranular" corrosion. There's plenty of WWII bits at the shop which are brittle as can be. Other pieces of the same alloy are not badly degraded at all, but are from different recovery sites. As far as a 40 year life, there's 1930s DC3s still at work, and subject to FFA commercial inspections. Not to mention DC9s, B52s, etc.!

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[breakeyp]

When I heard these things I was a Junior and afraid to question what I was told. They just stuck with me. I remember he was specific about short life of aluminum.

As for submarines, the diving and surfacing results in hull expansion and contractions which are the same a work hardening. The same as bending a piece of wire back and forth and it will eventually break.

I wonder how they determine metal fatigue other than looking for cracks? metals investigatins tend to be after the failure. I am under the impression that the old planes are less in number flying every year. Crashes or failed frame annuals? Not my area of expertise.

[jmoore]

I wonder how they determine metal fatigue other than looking for cracks?

All sorts of NDT methods. Visual, penetrant, ultrasonic, magnetic particle, eddy current, Xray, just to name a few. Aluminum has no lower stress limits at which cracks will not propagate under cyclic loads, unlike steel, so that complicates things a bit. But as far as predicting failures, experience and testing seem to be the usual methods of catching drams before it's too late. Life limits and all that.

ETA:For powerplants, that's about it as far as approved methods go, except for Thermographic NDI (used for composites), but that's not something with which I'm familiar.