Home Forums General Discussion Ask Dr. Peener Determination of peening intensity

How do I determine the required or industry standard "N" intensity for glass bead peening of cast Inconel 718 (AMS 5383). I currently process similar parts to an intensity of 6N based on a print call-out however this part does not have a call-out and I must be able to substantiate the peening intensity used. Thanks for your assistance!

Sounds like Xerox engineering, a common practice ;-) when there is no other information available. Are you the part owner or are you doing the peening for someone else? How similar are the geometries of your parts?

What exactly does the print for the part cite regarding the peening?

I am producing the part for a customer. The geometries are similar between the parts. My issue is that these are aircraft engine parts and the substantiation requirements are very strict. Determination by comparison is not the best means of substantiation. I have considered doing a surface stress analysis of a new OEM part to determine the intensity but this would be difficult and the results may not be difinitive. I have found tables that show standard practice intensities but my application always seems to fall of of the chart. Low intensities of 6N on substrates like inconel do not make it on to the chart. 6Ns are typical for aluminum but not high tensile steels. Is there a MIL or AMS that I can reference that would have tables that inlude an application like this.

Really, the customer should be giving you the peening requirements, as they are part of the part's design and will certainly effect its life and performance. This may be a silly question, but have you asked the customer about the peening specs? I agree with you that determining the surface stress and backing into an intensity is not definitive and is not the way to go.

In this particular case, I am processing the parts for an operator under an FAA approval and not the OEMs approval. The OEM has, and excercises, its right to withold data such as this. The operator relies on the repair station, with the help of OEM manuals, to process the part correctly, so ultimately has very little input to the processing of the parts. When no OEM data is available, I have to generate my own substantiation in many cases. As an FAA engineering representative I can actually approve the data. However, not being a shot peening GURU, I have to rely on other experts to guide me in the right direction. I just can not believe that this is not published data. If glass peening of inconel is a standard industry practice, then someone has surely published the parameters and properties of the process.

I have a general aversion to "Xerox" engineering where peening is concerned because it cannot be expected to produce best results except in instances where component characteristics and service environment closely duplicate those for which the prior-used peening conditions were developed. In your case, however, it appears that your customer is not forthcoming with any useful or helpful information. The prior peening intensity you cited (6N)is not likely to be damaging and could reasonably be expected to be somewhat beneficial even if not optimal. Therefore, it is at least something on which to hang ones hat. I offer two strong caveats: 1. Do not overcover i.e. 100% coverage is plenty. 2. This is a casting, so if you are peening an as-cast surface, ensure that there are no surface defects e.g. cold shuts against which peening cannot be effective.
After all of this I hasten to add that there really is no such thing as an "industry standard" for peening any materials, information such as that in Table 4 of AMS-S-13165 notwithstanding. Peening conditions must be considered as component specific, taking into account material characteristics, component geometry and component operating environmentin particular.