reference to substantiate a braze repair

[KirbyWan]

I'm looking for a reference to substantiate a braze repair. I'm brazing an Inconel 625 doubler to an Inconel 625 part using a nickel foil braze per AMS 4777. MMPDS-01 only has shear allowable for copper and silver brazing both of which it gives as 15 ksi. I found the article "Design properties of brazed joints for high temperature applications" by R L Peaslee and W M Boam which shows graphically that nicrobraz brazing has better qualites then silver or copper brazing.

I want to use the 15 ksi figure, which would give me a large margin of saftey, but I can't find any specific reference to substantiate that number. Does the community have any references I can use, or would referencing this article be enough? The article does not deal specifically with the materials I am using but s 590 (ams 5770) and nicrobraz 125.

Thanks,

-Kirby

 

[rb1957]

i'd use the 15ksi for Cu/Ag brazing as being conservative, and it gives a large margin.

otherwise, test it.

 

[KirbyWan]

rb1957,

Using the 15 ksi figure is my goal, but If the FAA or our DER comes back and asks "what's the basis for this number?", I want to be able to say I referenced it from such and such a data source.

To expand on my question just a bit, what is considered valid data to base a repair on? For materials and fasteners MMPDS and AN/NAS/MS specs are a great source. What do you use when the material is not listed? (Or "Don't use materials that are not listed!") Or a fastener that does not have shear or tesile properties such as AN123301-450. I couln't find shear data on this solid rivet. (I used the Fsu from MMPDS to calculate the shear, but again this was for a different standard AMS 5540 instead of AMS 7232.)

I'm alwasy uneasy using the tensile lap shear properties for adhesives in product tecnical data, because I know that information is based on a carefully controlled bonding procedure. While I feel our bond shop is very capable I expect somewhat lesser properties just from natural variation. I usually try to use the qualification requirements such as for BMS5-101 for adhesive properties.

What are some other best practices that can be used or when is a test the best approach? I am committed to designing good repairs, but I don't always know the best places to find valid data or how closely 'related data' needs to be before it can be used.

I mostly work on secondary structure such as nacell systems for GE and PW engines (inlets, fan cowls, thrust reversers, etc.) though I keep in mind that what brought the Concord down was a repair strap that fell off of a thrust reverser from the previous aircraft. I don't want to be the guy who designed (or installed) that repair.

I'm always willing to learn.

-Kirby

 

[WKTaylor]

KirbyWan...

Brazing is a materials and process driven assembly method. So materials and process must be developed and tested to assure accuracy of calculations.

Calculations are typically based on the braze metal properties, area, part-gap, voids, class, etc.

I strongly urge You to get the following as "starter" references.

AWS BRH Brazing Handbook.

AWS C3.2 Standard Method for Evaluating the Strength of Brazed Joints

SAE ARP573 Silver, Copper and Nickel Alloy Brazed Joints for Aerospace Propulsion Systems

MIL-B-7883 [CX'ed] BRAZING OF STEELS, COPPER, COPPER ALLOYS, NICKEL ALLOYS, ALUMINUM AND ALUMINUM ALLOYS

Regards, Wil Taylor

 

[KirbyWan]

Wil,

Thanks for the references. I had already looked at the Mil spec you offerered. The main piece of info I gleaned from that was the inspection limits. I'll look up the AWS and SAE references. From the titles they look exactly like what I am looking for.

BTW I would also like to thank you and the other heavy hitters that make this forum such a valuable resource. Your explanation of the difference between Hi-lok and Hi-lite pins and numerous other contributions have been a great resource.

I plan on going to the Boeing Structual repair for engineers part 1 in September, which I'm excited about.

-Kirby