Quantifying value of legacy shot peen on pinion

[UCengno1]

I am reviewing the value of retaining a shot peen process on a carburized, low alloy pinion. The pinion is subjected to an initial shock load at start-up followed by a 1-3 sec duration steady load. Operating speed of 3-5k rpm and it must last in the neighborhood of 10k start cycles. The application is successful with the peening opertion and has never been tested without it.

My experience with the use of shot peen has been primarily qualitative as a measure to boost fatigue resistance and have never been tasked with quantifying its importance. Is there any means by which to quantitatively review the effectiveness of shot peen? Do I isolate the component and look only a repetitive loading via testing or are there new analytic measures?

BCK

 

[unclesyd]

I think the first site will get you started. Aside from the posted page there is a wealth of information available on thi site.

http://www.shotpeener.com/learning/gears.htm

You will need to register and then go to downloads and download the "Green Book".

http://www.metalimprovement.com/index.php

Also if you will checkout NASA you will find a lot of information on shotpeening.

 

[swall]

At some point, after you get up to speed, you will need to do comparative fatigue testing--peened vs unpeened. No way to get around that.

 

[UCengno1]

unclesyd / swall

Thanks for the feedback. I saw testing in the crystal ball but was unsure if any other verification analyses had been developed.

BCK

 

[rmw]

You might look around some aviation sites or even post this question in some of the aviation forums since peening is extensively used in rotating aircraft parts (like helicopter blade system parts.) They may have some testing or information that would be beneficial to you.

Unclesyd beat me to my recommendation which would have been Metal Improvement. The branch that I used for some gear parts also did a lot of parts for Bell Helicopters near their location.

rmw

 

[MrMyers]

As mentioned above, peening is used in a wide range of industries, however, as far as I am aware, its affects are not often quantitatively used in an analysis to prove design life of a particular component.

The life of the component is predicted based on other methodologies without taking the peening in to account. The component may then be peened to subsequently lower risk of initiation as an 'extra added conservatism' for the life-critical region.

 

[unclesyd]

One thing not mentioned with a legacy product is that it probably stated life in a plain Jane configuration. In your case if was probably carburized and somewhere along the line an increase in fatigue life was needed and it was decided to shootpeen the gear for this increase. I seen this scenario carried out many times where the existing component wasn't quite good enough or had some bad design or machining features so we went looking a 10-15% increase in fatigue life. For years there wasn't much literature available as to the benefits of shotpeening other than people understood that it couldn't hurt and was supposedly made a better part. What I've seen happen is that product contains shotpeened components that allowed for an
incremental increase in loads or speed which is quickly used up by the user. When a replacement comes it may not have the increased capacity and one quickly finds they have serious failure problem. We had this happen on several gearboxes where the original manufacturer went out of business and the replacements looked the same but weren't.
Testing is OK but make sure you understand the end use of the product by asking numerous customers.

 

[israelkk]

MIL-P-81985 Peening of metals
SAE-AMS2430 Shot Peening
MIL-S-13165 replaced by SAE-AMS-S-13165 Shot peening of metal parts

 

[TVP]

Quantification of shot peening effects is frequently done using x-ray diffraction. Suppliers of highly loaded springs (automotive engine valve and fuel injection springs, suspension coil springs, almost any aerospace spring, etc.) use x-ray diffraction (XRD) to measure the amount of compressive stress in the surface and near-surface region and correlate this to fatigue life. The shotpeener.com website will have numerous papers that discuss XRD, the effect of maximum compressive stress at the surface, the depth of compressive stress, the effects of shot size & velocity on compressive stress, etc.

 

[Neubaten]

In my opinion, there's no use for a calculation on fatigue life if shot-peening is used. Bear in mind that I'm not a believer in fatigue life calculations. They tend to overlook many principal factors that can greatly vary the outcome.

You can calculate the fatigue life of a given part, with the greatest theoretical accuracy, but if this bart is, for example, bent, and the grips of the bending machine leave the smallest strech mark that could serve as a crack initiator, this will poo-poo all those beautiful calculations.

This is extremely certain in the case of hardened or pre-tensed shot-peened steel parts if you don't have a special consideration in certain factors.

Imagine that you have a tolerance for decarburization of 0.05mm or 0.10mm max, which is not uncommon for automotive structural parts. Under the same shot-peening process, the results obtained will greatly vary if you receive your parts free of decarburization, or near to the max tolerance. Which not so hard to predict of you think a bit about the process.

And so forth and so on.

I think the only reliable data is for tests of peened vs. non-peened parts. Using always the exact same manufacturing process as in production parts under study and using exactly the same shot-peening parameters as intended for the final manufacturing process, (shot type, shot size, shot hardness, almen intensity, cycle time, kind of machine, same granulometry, etc...)