Aluminum Alloy Fatigue Information

In summary, the author is looking for fatigue data for aluminum alloys, but is having difficulty finding any. There is data available online, but it is limited.
  • #1
minger
Science Advisor
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Hey guys, I'm working on a project and am looking for some fatigue data for aluminum alloys, A356-T6 in particular. I've looked through the MIL-5 and Aerospace (Cindas) handbooks and haven't found any decent information.

The textbook I have "Mechanical Engineering Design" by Shigley and Mischke only lists data for steel and other steel alloys. Does anyone have any decent references for stress vs cycles or anything decent?

Thanks,
 
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  • #2
The data is available out there, it's just a matter of whether you're willing to pay for it or not. SAE has a fatigue design handbook that might have some data in it. Otherwise, a quick search on Google turned up this ScienceDirect.com journal article:

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W7V-42DRCFD-8&_user=7150423&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_version=1&_urlVersion=0&_userid=7150423&md5=0b0a18db6a2b5b8f86b8bb101b0a3dc6
 
  • #3
Hi Minger. Good fatigue data on aluminum is hard to come by, especially charts showing test results.

MatWeb has some data depending on whether it's a http://www.matweb.com/search/DataSheet.aspx?MatGUID=595aeac7a5af4446bf4d912226644759" cast. Note the ASTM specs for these are B26 (sand) and B108 (perm mold).

I've designed a number of sand cast parts are highly stressed and under cyclic conditions and the only data I've been able to find is the matweb stuff which I've had to depend on. Seems to be ok, though I've always put lots of extra margin in.
 
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  • #4
Well, the only thing I could find off of there was the Fatigue Strength for 5e8 cycles, which can be useful, but I really wish there was some more data, an Ultimate Fatigue Strength would be nice; as then I could apply my own Marin endurance modifying factors.

Either way I appreciate the help, I guess I'll go through the library and see if there's any good fatigue books.

Thanks again,
 
  • #5
minger said:
Well, the only thing I could find off of there was the Fatigue Strength for 5e8 cycles, which can be useful, but I really wish there was some more data, an Ultimate Fatigue Strength would be nice; as then I could apply my own Marin endurance modifying factors.
The problem with aluminum is it doesn't have a typical 'fatigue limit'. The more stress cycles that are imposed on aluminum, the lower the stress cycles need to be to eventually result in failure. This is different than steel which has some distinct endurance limit.

If you were to plot peak alternating bending stress (y axis) against a log scale of life cycle (x axis) you'd find a knee in the curve at around 10^7 cycles. So that by 10^8 cycles, the graph is almost flat. It isn't flat though, it continues to decline, meaning that as you continue to impose more cycles on your test specimen, the peak alternating bending stress needed to result in failure continues to drop.

The most important things to understand about fatigue calculations isn't the specific limit of the material anyway. With the data MatWeb gives, one can be pretty sure where your stresses need to be to create a safe design. The more important issues are always things like stress concentrations, surface finish and absolute magnitude of loads and in what direction. These are the factors that I've found are typically not properly accounted for. In addition, realizing how far off some of these factors can be, in addition to how far off your real life loading conditions may be, the best thing to do is to be conservative in your design and ensure the safety factors you select reflect this lack of accuracy.
 
  • #6
Awesome, well I appreciate the help. Turns out my still-active ohiolink.edu account let's me pull some of that experimental data up.

I should be good to go now for what I need. Thanks again!
 
  • #7

1. What is aluminum alloy fatigue?

Aluminum alloy fatigue is a phenomenon where an aluminum alloy material experiences damage and failure after repeated cycles of loading and unloading. This is a common concern in engineering and design, as it can significantly affect the structural integrity and lifespan of a material.

2. What causes aluminum alloy fatigue?

There are several factors that can contribute to aluminum alloy fatigue, including material composition, loading conditions, and environmental factors. Some common causes include stress concentrations, corrosion, and improper heat treatment.

3. How is aluminum alloy fatigue tested?

Aluminum alloy fatigue is typically tested by subjecting a sample to repeated cycles of loading and unloading, often using a machine called a fatigue tester. The number of cycles and the applied load are carefully controlled and monitored to simulate real-world conditions.

4. Can aluminum alloy fatigue be prevented?

While it is not possible to completely prevent aluminum alloy fatigue, it can be mitigated through proper design, material selection, and maintenance. This includes avoiding stress concentrations, selecting appropriate alloys and heat treatments, and regularly inspecting and monitoring for signs of fatigue.

5. How is fatigue information used in engineering and design?

Fatigue information is an important consideration in engineering and design, as it helps determine the safe operating limits and expected lifespan of a material. This information is used to design structures and components that can withstand repeated loading and unloading without failure, ensuring safety and reliability.

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