Media size / Intensity limitation

Posted by: Walter

Media size / Intensity limitation - 03/05/18 10:27 AM

I'm looking for a chart / information that would detail the intensity limitations for a given size of media. I'm particularity interested in glass beads, but this would be good information for any type / hardness of media. Far to often I'm seeing drawings call out a size of media that is really too small to get the job done for a given intensity range. Either it's physically impossible to do what they are asking. Or by peening at extremely high velocity the glass bead explodes on first contact and or the part is not really being peened, it's being abused.
Posted by: Dave Barkley

Re: Media size / Intensity limitation - 03/05/18 11:36 AM

I think this is something that the Purdue CSEE could handle with ease and would be beneficial to the industry. Other than that, we could solicit intensity results for various medias and database it.

It would have been nice if we (at EI SPT) would have logged this type of data at our on-site visits over the years.
Posted by: Jack Champaigne

Re: Media size / Intensity limitation - 03/05/18 12:10 PM

I have often wondered if there should be a lower limit on intensity application based upon media size since small media at high intensity tends to "bury itself" into the surface. I speculate that each impact would therefore have significant tensile stresses near the periphery of the impact leading to failure nucleation.
Posted by: Robert Stone

Re: Media size / Intensity limitation - 03/07/18 10:57 AM

Jack, I'm not trying to hijack your train of thought, but I am a firm believer that there should be an upper intensity limit based on media size. In my experience, damage is induced well before small media buries itself into the workpiece.

I know of multiple tempered martensite steel products in the spring industry where small shot at high velocities produced a subsurface defect whose presence correlated very well with significant reductions in fatigue life.

Modifying the process to use larger shot at lower velocities to produce the same intensity eliminated the subsurface defects and greatly improved fatigue life. (In one case, the fatigue life more than tripled.)

So, here is a situation where there is no detectable surface damage but fatigue life is greatly impacted by the details of the peening process.
Posted by: Andy Levers

Re: Media size / Intensity limitation - 03/07/18 11:28 AM

I think the practical solution would be put an upper limit on the dimple diameter acceptable on a specific material, which in itself can then be related to media size, media type and ultimately intensity.

Its probably something that the OEMs would be best placed to do within their respective process specifications. However, I wonder if some guidance materials could be produced via one of the SAE committee's...
Posted by: Jack Champaigne

Re: Media size / Intensity limitation - 03/08/18 08:50 AM

Andy: you are spot on. Now all we need to do is find who will support the research with time and effort. Perhaps we can get the ISCSP involved since they are the world-wide experts. With funding we could get work done at Purdue or perhaps Ecole Polytechnique.