Landracing Forum
Tech Information => Technical Discussion => Topic started by: 38Chevy454 on July 03, 2012, 06:14:04 PM
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I told Jon last year at Speedweek I would put a metallurgy article together. I hope this works, I made it an attachment pdf. Never tried an attachment before.
I am a metallurgical engineer. My hope is that you can gain better understanding of the technical basis why metallurgy related things are the way they are. I tried to keep it in easy terms and language, not getting too caught up in level of details that are not needed for this level of understanding. Get a beer and read it :cheers:
Please ask any questions and i will try to answer them here.
Looking forward to Speedweek again! Unfortunately just as a spectator again..... My 55 Stude coupe project is not making any progress last few years. :oops: Terry
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Nice document Terry, I'm sure many will find it to be a very useful resource.
Larry
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Terry,
Great job! Looking forward to your up coming articles. I really haven't thought about Body Centered Crystals and Face Centered Crystals since I was taking metallurgy from H.P.Davis back in 1964!!! Again "Great Job"!
A little side story (can't get away from these with old men!) I did some work for a company that made (makes) very sophisticated casting machines that control the rate of poor and also the rate of cooling. The big product that is made with these machines are titanium compressor blades for jet engines. Using their method they can cast a complete compressor blade, almost net size, that is one crystal of titanium. As I understand the actual physical properties, tensil and yeild strength are not very affected but the fatigue life is very significantly extended, no inter crystal surfaces. Any comments?
Rex
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Thanx Terry. I've been looking for the one you shared with me 3 or 4 years ago and was gonna ask you about it. This is a huuuuuuuge help. See you in a month or so. :cheers: Wayno
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Terry:
If memory serves me well (and I think it does but I can't remember for sure) - you did send something like this to me for my inspection and approval - right? And I got it lost in the pile of stuff and never moved ahead with it - moving, that is, by telling you to go right ahead and offer it up to the forum?
Well -- I apologise for my sloth but offer hurrahs to you for getting this posted. It's pretty good - 'specially in that for me, a liberal arts major, it offered stuff that answered questions and brought a bit of enlightenment. So therefore I say unto you - if the rest of the folks that comment on the article agree, I'll install it in the Tech archive on landracing.com.
Thanks for the work.
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Hi Rex, yes, single crystal blades are used in turbine engines. Mostly for the hot section where the temps are extreme. Most of the baldes are nickel and other very high temp oxidation resistant materials.
On your specific question, the grain boundaries are where it is easier for fatigue cracks to initiate. Fatigue cracks grow as transgranular, so the crack surface is flat typically a semi-elliptical shape. Fatigue cracks are the most common as they are a result of cyclic loading under the yield strength. Almost all cracks you find on your racecar or anything that has cyclic loading will be a fatigue crack. The key is to keep the stress level low enough the crack does not initiate or propagate, called fatigue limit. Not all materials have fatigue limit, but steel does and aluminum does not. This is why alum connecting rods have a set life, they will develop a crack eventually. Another key to reduce fatigue is limit the stress concentration. Smooth fillets as opposed to sharp radius, gussets vs unsupported corners on tubing, etc.
One thing that is a bit unique to the single crystal is that they can orient the structure for optimum result in one direction. Most product you buy is rolled and has best properties in the longitudinal (think length) direction. The long transverse (think width) is a bit less and the short-transverse (think thickness) is the worst. Always try to orient stress in longitudinal or long-transverse if possible.
Kind of contrary to the single crystal is that very small grain size is generally better than large grain size. Smaller grain size is beneficial to most properties. This is why heat treating you need to watch for excess time at temp, it causes grain growth. You can;t really control grain size in what you buy however. Sorry for the rambling reply.
Terry,
Great job! Looking forward to your up coming articles. I really haven't thought about Body Centered Crystals and Face Centered Crystals since I was taking metallurgy from H.P.Davis back in 1964!!! Again "Great Job"!
A little side story (can't get away from these with old men!) I did some work for a company that made (makes) very sophisticated casting machines that control the rate of poor and also the rate of cooling. The big product that is made with these machines are titanium compressor blades for jet engines. Using their method they can cast a complete compressor blade, almost net size, that is one crystal of titanium. As I understand the actual physical properties, tensil and yeild strength are not very affected but the fatigue life is very significantly extended, no inter crystal surfaces. Any comments?
Rex
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Hi Jon, yes I did send it to you a while ago, but not a worry. I figured just get it out here and let people see it to generate comments and questions. Putting in tech archive would be a good idea. Terry
Terry:
If memory serves me well (and I think it does but I can't remember for sure) - you did send something like this to me for my inspection and approval - right? And I got it lost in the pile of stuff and never moved ahead with it - moving, that is, by telling you to go right ahead and offer it up to the forum?
Well -- I apologise for my sloth but offer hurrahs to you for getting this posted. It's pretty good - 'specially in that for me, a liberal arts major, it offered stuff that answered questions and brought a bit of enlightenment. So therefore I say unto you - if the rest of the folks that comment on the article agree, I'll install it in the Tech archive on landracing.com.
Thanks for the work.
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Hello from another Metallurgical Engineer. I haven't had an opportunity to read the article yet, but I'm glad to know I'm in good company.
Steve.
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Terry,
Thank you so much! We EE's appreciate simple stuff.
Don
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Terry,
I'd like to thank you for such a concise explanation on ME . Do to the nature of the business I'm in, ME plays a very critical roll. Most of the folks that work hear have a good understanding of what materials work best for any given specific project, but not entirely sure why.
I am going to print your PDF and pass it around to the guys to read. Hopefully that will help them understand why I get so hard headed about material selection for some parts.
Thanks for the post, I think any car builder should take a close look at it.
Rouse
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Terry I must say you simplified this very good I remember when teaching you would lose the student as soon as you tried to get them to understand the dendritic growth of a crystalline structure during solidification. I have not taught for 7 years and surely miss it. I look forward to your next article this is the stuff that is made for sitting on the technical library and having a good read.
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Nice article. Still too technical for a lot of people, but there is only so much you can do to simplify technical articles.
If you don't understand the chemistry and physics at the atomic level, you are never going to go fast.
Heck, I even bought "On Food And Cooking". "The Science and Lore of the Kitchen". Having the chemistry and physics explained makes me a better cook too!
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Yesterday I was goofing around in the shop and experimenting with digital photography. The first picture shows a fatigue failure of a SawZall blade. Note the coarse crystalline structure. This indicates a fatigue fracture.
Next, The blade was bent and broken in a vise. The second photo shows this.
A tensile fracture, not related to fatigue, results. Note the fine crystalline structure. This is shown in the third picture.
Broken metal parts subject to cyclic loading often show both types when examined. Usually there is a stress riser somewhere. This is an irregularity, defect, or discontinuity that concentrates stresses. Adjacent to this is a zone of coarse crystalline surface that indicates a progressing fatigue fracture. Finally, the cross-sectional area of the part is reduced enough to fail in tensile fracture. The fine crystalline structure shows where this occurs.