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[Nadimuthu]

We have an order for supplying sand castings in Aluminium 319 alloy.Our customer wants to know what is the maximum stress to failure for a 20 million cycle loading?
Data available in the ASM Handbook "Specialty"Aluminium has information only for 5 million cycles/
Request help from some you experts>

Regards,
Nadi.

 

[TVP]

There have been a couple of recent articles on the fatigue behavior of aluminum alloys like 319 at very high cycles-- up to 10¹⁰. One article that was quite informative was "Demonstration of an Endurance Limit in Cast 319 Aluminum" by M. J. Caton, et al in the January 2003 issue of Metallurgical and Materials Transactions A. Alloy W319-T7 was analyzed, with three different solidication times (Low SDAS = 44 seconds, Medium SDAS = 970 s, & High SDAS = 2200 s). An endurance limit was found for all three conditions, with the low SDAS samples obviously having better mechanical properties and fatigue performance than the other two groups. Low SDAS = 23 micrometers, Medium = 70 micrometers, & High = 100 micrometers. Endurance limit (stress amplitude) was approximately 56 MPa for low SDAS, 40 MPa for medium SDAS, and 35 MPa for high SDAS.

 

[NickE]

TVP -- Does this raise questions as to the accepted rule that aluminium alloys have no endurance limit? It seems to me that it would. As this is a cast alloy I wonder if the wrought alloys will show the same behavior. Also seems that the heat treat condition should have some effect on the fatigue behavior. I notice the above applies to T7 condition hmmm.. wonder if the overaged or underaged would have better results.




Nick
I love materials science!

 

[TVP]

NickE,

Yes, this does conflict with the generally accepted notion that aluminum alloys do not exhibit an endurance limit. The authors discussed this in the above-mentioned paper, and one idea that was discussed is that the endurance limit may only appear after 10⁷ or 10⁸ cycles for cast alloys, and maybe only after 10¹¹ or greater cycles for wrought alloys. There is a lot of activity in this area with respect to fatigue crack initiation, critical flaw size, etc. One of the key aspects of this research is the use of ultrasonic testing equipment which makes it possible to test to very high cycles. All of their samples were tested in less than 1 month, whereas testing on a single servohydraulic test frame would have required 24.7 years!

Another contemporary paper on this topic is "Microstructure-based fatigue modeling of cast A356-T6 alloy" by D. L. McDowell, et al. It appeared in Engineering Fracture Mechanics 70 (2003) 49-80. Elsevier is still offering a complementary copy of this issue for viewing on their website. Use the following link for the article:

http://www.sciencedirect.com/scienc...md5=9db3c1ee11251782c11017325f3b0c2f&ie=f.pdf

 

[NickE]

Thanks TEV- this is really good reading to keep at least my head current on research in met/mat.

nick

 

[TVP]

Yeah, that TEV guy is pretty knowledgeable. I would have given him a star, but the system wouldn't let me. Hmm....

 

[NickE]

Sorry man....

nick

 

[TVP]

Not a problem, Nick. I was just goofing around...