shotpeening of machined fittings ? 2

[rb1957]

Hi guys,

Does anyone (Will ?) have references for the need to shotpeen machined fittings ?

I am looking for myself, but I guess here is a good source of info.

We're being "challenged" to come up with a justification beyond "industry practice" when we call up shotpeening on fittings machined from thick billets, to address the corrosion concern (not for fatigue benefit, we keep that in our back pocket !).

another day in paradise, or is paradise one day closer ?

 

[LiftDivergence]

You might have a look at the following site - seems like there is a lot of good info on there including specifications and articles in the "library".

https://www.shotpeener.com/

I have always understood the primary benefit to be the improvement in fatigue performance and endurance limit as you mentioned. But if that is not something you want to bring up, there are a couple other ways to look at it.

First, as established, peening of any sort (shot, flap, laser, etc.) is a form of work hardening which primarily affects the surface (the tensile stress deeper in the part is increased, but mainly the surface is affected). The surface hardness is increased due to the plastic deformation. This increases the part's resistance to abrasion, which could be considered an additional benefit. There is something about this in my Materials book by Callister and Rethswich I think.

There is also data out there suggesting peening improves the stress corrosion performance of a part. Sounds like you want to avoid talking about fatigue benefits, but remember SCC is a distinct phenemenon: thread2-458851

Stress corrosion will generally progress along grain boundaries at the surface, which can be hardened by peening. If you search for "corrosion" in the library at the site above you will bring up some articles to reference.

Keep em' Flying
//Fight Corrosion!

 

[WKTaylor]

RB...

Lot of factors/info has to come together to provide a logical answer.

Alloy/temper/thickness of the raw stock? grain orientation critical?

A 100% machined part: (a) 'new designed'; or (b) to replace a part that was originally DF/machined?

What peening media and peening spec? What was YOUR 'value-added' intention for this process.

What is the machined finish requirement… and how is the surface machining' to be 'cleaned' up to attain this requirement?

What corrosion protective finish?

NOTE.
Peening has proven valuable for retarding fatigue-crack initiation and providing significant resistance to stress corrosion cracking and exfoliation corrosion. It is also used to mitigate surface embrittling effects of certain plating's and anodic coatings. I have this info somewhere... just have to figure-out where the 'non-proprietary' equivalent is in my 'stash of knowledge'.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[rb1957]

thx.

the back story … we typical call for saturation shotpeening when we machine a fitting from thick plate, so usually 7075T7351 but also 2024T3 and 6061T6; the idea being to close the grain boundaries (and not looking for a fatigue improvement). Now we're getting push-back … "this takes a long time to do, do we Have to do it ?". I believe this is typical industry practice though large OEMs (we're a "chop shop") would have much more definition on this. I'm prepared to say "ok, if you want to deviate from industry best practices then let's gather some data; corrosion test on …" and wade into that river until they give up !?

To Will's questions,
typically 7075T7351, sometimes 2024T351 or 6061T6
new parts (ie not replacement/repair parts)
my "value added" is corrosion "prevention" (yes, I know you can't prevent corrosion, but you can delay it)
clean up and finish as required, usually not much alodine & prime or anodize, top coat maybe, wash with WDC after installation maybe.

cheers,

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

rb… quick fly-by comments ONLY...

In general I never shot-peen 6061-T4 or -T6... little/no valued added. Attain/maintain 125-microinch RA machined finish [ASME B46.1]. apply chromate conversion coating [CCC] and primer/topcoat if/as needed.

7075-T7351 I recommend peening thick section parts that are heavily machined... especially if anodized prior to primer/topcoat. Otherwise I have to 'see' the value-added before I'd sign-onto peening... especially if 'simple' corrosion protection [CCC + primer + topcoat] is to-be applied. Exception: severe corrosion or sonic environment use could be a factor.

As for parts machined from 2024-T351 thick-plate... even though L-T and L properties are very good... this stuff can have very nasty tendency for SCC/EXCO/fatigue initiation issues in the short transverse [S-T, as-rolled thickness] orientation, due to low KIscc... and this temper is generally NOT recommended for use in heavily-machined thick sections without shot-peening.

NOTE.
As a rule... I try to have most thin and thick section parts... replacing 7075-Txxx machined/DF parts... machined from 7050-T7451 plate for a bunch of reasons I haven't time to 'splain'-in-depth. The multi-orientation, benign properties [S-T, L-T & L] high resistance of 7050-T7451 to SCC/EXCO and uniformly good fracture toughness usually make this stuff a no-brainer.

Material subs for ancient/deep-section higher strength alloys...7075-T6, 7178-T6, 7049-T6 [extrusions, plate and die forgings], etc... are the hardest... especially when the analysis shows low MS.

BTW...
Glass beads, ceramic beads and cast steel shot are typically used for peening aluminum... my preference is ceramic beads for a whole bunch of reasons.


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Sparweb]

You could address both the "industry practice" issue and the "reasons for it" in one stroke by pulling up the SRM for the aircraft in question.
The starting point is SRM 51-28-08 for the jets and SRM 51-24-00 for the turboprops you typically work on.

The link from LiftDivergence to shotpeener.com has no shortage of reference material.
This one has Goodman diagrams in it and everything:

https://www.shotpeener.com/library/pdf/1954013.pdf

And... there's a certain SAIT AET grad that you and I both know who should be able to dig up a document from the Bus company that states shot-peen gets a 15% credit on aluminum and steel and a 5% credit on titanium. 'Cause I love getting between you guys and your debates.

http://www.sparweb.ca

 

[WKTaylor]

Might find these useful... no particular order...

ARL-TR-4095 Shot-Peening Sensitivity of Aerospace Materials

MCIC-71-02 Shot Peening for Improved Fatigue Properties and Stress Corrosion Resistance

AMS2430 Shot Peening

SAE J2441 Shot Peening

SAE ARP7488 Peening Design and Process Control Guidelines

SAE HS-84 SAE Manual Shot-Peening

MIL-STD-852 [CX] Glass Bead Peening Procedures

Metal Improvement Company 'green book' 9th Ed - Shot Peening Applications

RB'57...

In the field [service engineer OS], I found it useful to glass-bead-blast aluminum parts for improved finish... especially somewhat rough surfaces to attain a ~125-microinch RA Shot-Blasted finish that had a 'uniform smoothed-matte appearance'... Local machine shop made their 'good-parts' look smooth/refined... and worked-well with CCC+epoxy primer.

MIL-STD-1504 Abrasive blasting [on aluminum alloys with glass or ceramic beads, only].

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[rb1957]

thx, will look into your references … I understand SAE HS84 is out of print (went looking for it, IHS says unavailable).

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

RB... I just checked IHS...

My company's subscription... the last available HS-84 [4th ED] is still available for download [I verified]. Legibility is sketchy... but 'does the job'...

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[rb1957]

'k, gremlins ?

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

RB... call your IHS customer service agent...they've helped me several times with issues like this!

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]