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Very interesting graph but duration at temp is the problem. I will make a few assumptions from this graph and toss them out:

1. Minor time excursions into the higher temps will not affect strength. Operating at 425 through TBO would affect strength appreciably but 15 minutes is not going to make any difference.

2. We must have safety margins built in even at max operating temp for these engines so we must be operating way down on that graph.

3. Fatigue strength is probably far less than tensile stress in the graph so we must have even a larger safety margin for fatigue protection and be further down the graph in normal ops.

4. Cylinder heads likely have both tensile and compressive loads. Tensile loads may be an issue or maybe high temps near the exhaust valve is the limiting issue with temps.

5. Rebuilding with previously flown cylinder heads could leave you with diminished protection in strength unless you know the temp history.

Thanks for that graph Fred.

Paul

On 2013-05-31, at 23:04, "Frederick Moreno" <frederickmoreno@bigpond.com> wrote:

<SENDER_EMAILfrederickmoreno@bigpond@@com.png>

Paul wrote:

"Colyn: I just re-read that article, Busch states:

(The head's tensile strength is reduced to 50% of its room-temperature value at a CHT of 400F, and to about 33% at 500F.)

I don't see that supported in any literature studying the properties of steel versus temperature."

The cylinder heads are ALUMINUM and the cylinders are steel. Attached chart shows that the 1000 hour strength of 356 aluminum alloy heads south rapidly as exposure temperature exceeds 300F.

Fred

<cz_Heat_Effect_on_Aluminum.JPG>

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