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Improving Frames with Micropeening and Other Residual-Compressive-Stress Treatments?

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Improving Frames with Micropeening and Other Residual-Compressive-Stress Treatments?

Old 10-30-12, 04:04 PM
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Niles H.
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Improving Frames with Micropeening and Other Residual-Compressive-Stress Treatments?

Laser Peening, Shot Peening, Ultrasonic Impact Treatment, Low Plasticity Burnishing, High Frequency Impact Treatments -- these are some of the approaches that have demonstrated significant improvements in strength and fatigue life, sometimes very significant improvements. Surface appearance, hardness and scratch resistance, notch resistance, crack and crack propagation resistance are also significantly improved.

In some cases, order-of-magnitude improvements are seen. Other times, it is more like 2X-5X.

I've just started looking into these treatments.

Independent Fabrication sells a shot-peened titanium frame. They are convinced of the merits of this treatment. More details are available on their site.

Google can provide additional information and links for all of these treatments, among others.

I thought others here might be interested. If anyone has anything to add on the topic, please post.

I already have a ti frame, and I am considering sending it out for one of these treatments. I have no idea how expensive they are, though, or which of them would be most cost effective, or who would be best to do it through. Any suggestions appreciated.

The idea of relieving residual tensile stresses seems excellent to me, as do the other improvements.

High Frequency Impact Treatments look as though they may even involve reasonably affordable tools.

Aluminum and Titanium seem like prime candidates for these treatments. Maybe some of the steels as well? Falanx? Anyone?
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Old 10-30-12, 05:00 PM
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I don't see how they improve the strength. They put a surface layer in compression, which helps avoid crack nucleation and initition. I worked in a place that used something similar to reduce cracking in holes, but I didn't stay there long enough to know if it really worked. I know the engine manufacturers have used shot peening for quite some time.
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Old 10-30-12, 09:56 PM
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The materials and processes that the bike business uses have evolved over the last hundred+ years and haven't yet taken advantage of the stress relieving that you mention. I wonder how much less weight can result with the stress relieving. We all know that the life span of frames are not the primary goal of manufactures. Andy.
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Old 10-31-12, 09:33 AM
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Really? We're still at that old chestnut? Shaving a hundred grammes off a frame while the rider piles on the pounds?

That's not entirely true. GT used to plastic ball bead burnish their frames, don't know if they still do, but it's essentially the same process, carried out with a softer impingement material to slightly lower deformations.

Basically every ductile engineering material would benefit from a shotpeening operation of some type. Yes, Unterhausen it really works, otherwise no-one would invest the time or effort in doing it, especially not in aerospace, where it's routine and often fundamental. It also lowers the incidence of stress corrosion cracking and corrosion rates. The important aspect is that all the surface is worked plastically and none of that material is removed by the impingement material. Thats why polished steel balls or plastic beads work wonderfully well on steels and aluminium respectively.

Increases in direct UTS are rare and low, as the total volume of material work hardened is very low, but in practical terms a structure with an extended or raised fatigue life or limit gives the illusion of greater strength.
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Old 11-01-12, 07:44 AM
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You would think that all the theorists going on about frames hardening(or is it softening?) over time would say that just riding a frame relieves stress in the material or hardens the outside with all the pummeling it takes......
Bike companies don't really want their frames lasting longer than the warranty. What would the point of that be? Frames are like lightbulbs. Gotta burn them out to keep the cash flowing.
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Old 11-17-12, 06:51 AM
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Originally Posted by Falanx View Post
Really? We're still at that old chestnut? Shaving a hundred grammes off a frame while the rider piles on the pounds?

That's not entirely true. GT used to plastic ball bead burnish their frames, don't know if they still do, but it's essentially the same process, carried out with a softer impingement material to slightly lower deformations.

Basically every ductile engineering material would benefit from a shotpeening operation of some type. Yes, Unterhausen it really works, otherwise no-one would invest the time or effort in doing it, especially not in aerospace, where it's routine and often fundamental. It also lowers the incidence of stress corrosion cracking and corrosion rates. The important aspect is that all the surface is worked plastically and none of that material is removed by the impingement material. Thats why polished steel balls or plastic beads work wonderfully well on steels and aluminium respectively.

Increases in direct UTS are rare and low, as the total volume of material work hardened is very low, but in practical terms a structure with an extended or raised fatigue life or limit gives the illusion of greater strength.
GT used steel balls to burning their frames in 6' diameter steel drums with internal floating fixtures that held four frames. The fixture was designed to move around the inside on the drum during the process. The drum had a truck wheel on on each end that rode on an industrial pipe rolling machine. Pretty simple stuff.

The drum spins at a pretty slow speed, with small scoops bringing the balls up and dropping them on the frame in random patterns. For an aluminum frame, it's the best thing you can do to reduce failure once the heat treating is completed. In addition, the surface compression provides a beautiful, lasting finish. Have you ever seen a GT that wasn't shiny? That is raw 6061.

It takes 10 mins to process the frames, right out of heat treating and right into a shipping bag.

I found a machine for free but it would cost a lot to get installed and filled with 1500 lbs of steel balls. It also makes a lot of dirty water.

No theory or illusion. People do actually test things sometimes.
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Old 11-17-12, 04:15 PM
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Originally Posted by ftwelder View Post
GT used steel balls to burning their frames in 6' diameter steel drums with internal floating fixtures that held four frames. The fixture was designed to move around the inside on the drum during the process. The drum had a truck wheel on on each end that rode on an industrial pipe rolling machine. Pretty simple stuff.

The drum spins at a pretty slow speed, with small scoops bringing the balls up and dropping them on the frame in random patterns. For an aluminum frame, it's the best thing you can do to reduce failure once the heat treating is completed. In addition, the surface compression provides a beautiful, lasting finish. Have you ever seen a GT that wasn't shiny? That is raw 6061.

It takes 10 mins to process the frames, right out of heat treating and right into a shipping bag.

I found a machine for free but it would cost a lot to get installed and filled with 1500 lbs of steel balls. It also makes a lot of dirty water.

No theory or illusion. People do actually test things sometimes.
I was always of the understanding that GT used polymer beads. I stand corrected. In which case, they must have been some pretty bloody expensive BBs to have the minimum silky smooth polish not to chew the surface alloy.

See what I mean by lowers stress corrosion? :-)

Really? They've measured actually statistically valid increases in bulk UTS from deformation layer just one hundredth of the section thickness?
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