How much wear is acceptable? 1

[KirbyWan]

So if there is a wear mark from rubbing, how much wear is acceptable. I have often seen a figure of 10% wear as being minor, and occasionally 20%, but is there any accepted data I could use to substantiate leaving the wear mark and just blending the damage to a smooth contour.

Generally I'm dealing with secondary structure, nacelle systems and what not. In this specific instance I have a fitting on a translating sleeve that is a lug .295 thick and .625" wide with a wear mark .035 deep by .250" wide, and smooth bottomed where the actuator was rubbing against the fitting. So this is over the 10% the thickness, but a cross sectional loss of only 2.4% which in my engineering judgement is minor.

Without specific allowable damage limits is there any accepted data I could use justify this?

What factors should i be thinking about when making a judgement call like this? (Obviously primary vs. secondary structure but also sheet metal, vs. bonded structure vs. fittings with lugs etc.) Which of these would make sense to have a more restrictive limit compared with others which would be less critical?

What would be a reasonable cross sectional loss to have as a hard figure to not exceed? I was thinking perhaps 5% cross sectional loss after blending to a smooth contour would be acceptable.

Thanks,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[rb1957]

if you've got rubbing i'd worry about "why?" ... remember it was "rubbing" between fuel pipes that brought down an A330 over the Atlantic ... Air Transat, luckily a safe landing.

at a minimum I'd put something between the worn parts, as a sacrificial wear strip.

As for the worn parts, I'd look at where they're worn. presumably there's nothing in the SRM (I'm sure you'd've looked first).

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

 

[KirbyWan]

This is where the thrust reverser deploy actuator connects to the translating sleeve. The connection has a spherical bearing and it looks like there was enough play for the end of the actuator to make contact with the fitting. I was thinking of bonding a .020 thick stainless steel or 7075 doubler to prevent damage from future wear. I could use this material to come up with some numbers that say the strength is restored, but for a fitting this size, I kind of know that critical loads would not be transferred if this fitting was loaded to design limits. So I feel uneasy using a justification that I know is suspect.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[rb1957]

sounds like good judgement ...maybe "return to supplier for repair or scrap". The supplier (manufacturer) are the guys with the numbers. I suspect that they'd like to know that their mechanism has to potential for unexpected wear.

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

 

[MikeHalloran]

I'd wonder if there's a way to install the actuator so it doesn't rub, i.e., the intended way, and why it's even possible to install it in an unintended way.

... not that I have ever designed anything that could be installed wrong.






Mike Halloran
Pembroke Pines, FL, USA

 

[KirbyWan]

Yeah, I think we're going to go to Boeing to have them create a repair. It seems like of the 12 fitting for the ship set of reversers there are 3 with wear marks. Might just be a rigging issue.

I was mostly hoping for direction on substantiating what I think of as a standard practice but nowhere covered by what I think of as accepted data for a repair. Also for more experienced hands to share their estimate of what wear limits are acceptable in various situations.

Thanks,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.