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Why Use Chicken Rivets?  
User currently offlinejorisdebont From Netherlands, joined Sep 2012, 10 posts, RR: 0
Posted (3 years 7 months 1 week 5 days 2 hours ago) and read 7581 times:

I was at the Delft University of Technology last week and someone there told me about chicken rivets. Some parts of the wing can be glued and/or welded into place, no need for rivets. But they still put a few rivets into the wing to secure the part that has al ready been welded there. The rivets serve no purpose except for giving the self reasurance that there are some rivets there. Why do engineers put in these rivets?

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4 replies: All unread, jump to last
User currently offlineDalmd88 From United States of America, joined Jul 2000, 2891 posts, RR: 14
Reply 1, posted (3 years 7 months 1 week 5 days 1 hour ago) and read 7542 times:

I've never worked on any structure that has these but a quick search yielded redundant load path and peel back prevention in case of adhesive failure. Sounds like they are common in some newer biz jets like Gulfstreams.

User currently offlinehorstroad From Germany, joined Apr 2010, 361 posts, RR: 0
Reply 2, posted (3 years 7 months 1 week 5 days ago) and read 7505 times:

fail safe
if the welding/bonding fails the rivets take the load. will probably never happen, but better be safe than sorry

User currently offlinetdscanuck From Canada, joined Jan 2006, 12710 posts, RR: 78
Reply 3, posted (3 years 7 months 1 week 3 days 22 hours ago) and read 7099 times:

Quoting jorisdebont (Thread starter):
Some parts of the wing can be glued and/or welded into place, no need for rivets.

Yes. It's typically referred to as "cold bonded" or "hot bonded."

Quoting jorisdebont (Thread starter):
But they still put a few rivets into the wing to secure the part that has al ready been welded there.


Quoting jorisdebont (Thread starter):
The rivets serve no purpose except for giving the self reasurance that there are some rivets there.

No. They have a purpose.

Quoting jorisdebont (Thread starter):
Why do engineers put in these rivets?

As horstroad said, if it's a fail-safe design the rivets provide backup in case the bond fails. Unlike a bond, rivets tend not to individually fail all at once unless you're talking about multi-site damage (like the 737 "convertible").

If it's a damage tolerant design, which is a lot more likely for today's designs, then the rivets greatly simplify your inspection plan. Assuming the rivets can carry limit load (which is the normal design criteria) then you only need to inspect the joint about every 1/3 to 1/2 of the *rivet* fatigue life. If you don't have the rivets, you have to do the much more difficult bonded joint inspection more often.


User currently offlineKPWMSpotter From United States of America, joined Dec 2006, 502 posts, RR: 2
Reply 4, posted (3 years 7 months 1 week 3 days 21 hours ago) and read 7048 times:

The "chicken rivet" methodology is a hold-over from the early years of structural adhesive technology and realistically is no longer necessary. In the era of the 707 and DC-9 very little was known about adhesive reliability and generally the quality of bonding was quite poor. Rivets and mechanical fasteners were well known and were added for redundancy.

These days, structural adhesives are usually much stronger than the metals skins they are holding together, are corrosion resistant, and are fatigue resistant. Structural bonding can out-perform mechanical fasteners in many cases. In some cases, the addition of mechanical fasteners actually detracts from the effectiveness of the bonded technology.

Most MD-80 and 737-series flight controls (spoilers, ailerons, flaps) are constructed of bonded honeycomb wedges. Some of these surfaces (especially on the MD-80 series aircraft) also make use of redundant rivets which fasten into the honeycomb core. One of the biggest problems with honeycomb core is moisture ingression (which leads to disbonding, weight gain, corrosion, etc). The "chicken rivets" on these flight controls actually accelerate the failure of the parts, since the rivet holes provide a path for moisture to enter the honeycomb. Boeing has issued a number of standard repairs for these parts which replace the skins with adhesive only (no rivets) to improve the service life of the parts.

Initially, yes, chicken rivets were installed for redundancy. In modern composite structures they have very little use, and often cause more problems than they solve. That being said, improper use of adhesives can also cause problems (the aforementioned "737 convertible" was partly due to improperly installed adhesive interfering with a rivet joint), but that's a different topic altogether...

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