Post Shot Peen Material Removal/Surface Disturbance.

[SkyPunk]

Anyone have a quick sumation of what possible effects could be expected of the following. Aluminum forging shot peened with 200% coverage damaged appx .006 deep gouge appx 1" long .008" wide. Damaged area blended out 10/1(ish), and shot peen not replaced? Most allowables of surface material are 10% of shot peen intensity. This particular one works out to allow .001" material removal allowable. How severe, if any would the reduction in fatigue life be?

Thanks,

Skypunk

 

[40818]

Of the top of my head, i would say it would be entirely dependanty upon the loading situation of the part, and the location of the damaged area, it might be in an area that is of little problem.
If i read your post correctly, the damaged area went through the induced surface compression layer due to the peening process, and further reduced by the blend. I would probably recommend looking at the local stress raiser casued by a grooved notch (petersons etc) and rund some quick numbers. You could always re-shot pean the local structure though to re-introduce the compressive layer.

 

[groovitude]

Not sure of what the requirements for the part are, but we had a similar problem a while back with a landing gear actuator. It was determined that blending the damaged area was acceptable, but there were additional considerations that had to be met before the part was accepted. The part had to undergo a Fluid Particle Inspection (F.P.I.) to determine if there were any minute cracks or damage that could not be seen by the naked eye after the blending process. It then had to be shot peened locally. The part had also been anodized. Rather than send it out to have the anodize removed & then re-applied, it was determined that local irridite or alodine would be sufficient because the part was to be primed & painted afterwards. Not sure if any of this is applicable to your part, but this solution got us through.

 

[WhiteRabbit]

It is common practice to re-shot peen 7075-T6 and 7178-T6 forgings due to it's adverse SCC properties after disturbing the surface.

We generally never re-anodized a part due to the process involved. Most of the time the part would burn at the electrode contact points during the anodize (not to mention the adverse effects of anodizing to the fatigue properties).