Aluminum structural fatigue

[JD Cross]

My 91 is 20 years old and aluminum fatigue is on my mind.

I read somewhere that Honda thought our aluminum structure was sound for about 20 years. I am sure they thoroughly tested the aluminum structure of our cars and made sure they were conservatively engineered but other than the Porsche 928 I don't know of other cars of our vintage with an aluminum structure.
I read Porsche started to see aluminum fatugue after 10-12 years on their 928 and the cars value has suffered accordingly

Research shows that steel can handle bending/vibration cycles indefinitely if within it's design parameters.
Aluminum apparently has a much tighter range between bending/vibration acceptance and failure.

I am wondering if anyone has started to see any areas that are showing fatigue stress.

Jim

 

[A.S. Motorsport]

Personally i have never ever heard of or seen any structural fatigue in a NSX.
I do know a number of steel chassis KA7/8 Legend's have head structural failure after extreme abuse in combination with suspension/tire setups.

All i know off where high millage cars that ran on very bad roads iirc with low tire-walls, in the Legend community a lot blame over bracing the chassis with strut bar's caused it which i don't believe at all.

That being said chassis technical KA and NA cars have nearly nothing in common, and the aluminum sub-frames never failed in the KA's.

Anyway interesting topic let see what the aviation engineers have to see about this.

 

[docjohn]

at a past xpo...Fl I think, we were told the frame is designed for at least 30 years,what happens after that...who knows,so could 2020 be the new 2012?:wink:

 

[geometro]

I've heard of the 30 year figure also. Since Aluminum does not have a defined fatigue life, I think this figure is taking in consideration of driving it as a normal/sporting car around 10,000 mi a year. So unless you're getting close to 300,000 miles on the odometer, I wouldn't worry about it.

 

[Honcho]

If Honda's engineers are telling you 30 years, then plan on 150% of that number, or 45. Engineers always design conservative.

 

[Mac Attack]

That's called the safety margin factor. No one outside of a Honda NSX chassis engineer knows that, so I wouldn't say a 50% longer design life is a good number to use :wink:

Also, every car will be unique. For example, the 2000MY NSX from New York that has 100k miles on it, has had a stiff suspension and low-profile tires it's whole life may have it's structural design limits reached way before the 1991 MY 100k mile NSX with OEM suspension and OEM-sized tires driven on more normal roads.

Dave

 

[Huck]

Having had Porsche 928's for several years, I have never seen or experienced any metal fatigue and I drove them pretty hard. They were NOT built for performance racing but Autobahn crusing. The engines and transmissions were pretty bullet proof and the bodies did not rust. Most of suspension, like the NSX, is aluminum. That said, there is aluminum and there is aluminum. Some of the alloys are extremely strong ex--the 928 has aluminum lugs on the wheels. Their engine blocks are two piece with different alloys on the top then on the bottom---both being aluminum. never head of a 928 engine failure due to wear either.
Metal fatigue is not uncommon (BMW E36 are notorious for rear sub frame to body--metal fatigue failure especially with tracked cars). I had several Volvo 1800Es as well as early Mustangs with unibody where overpowering engine torque or weak shock towers would cause the metal to twist a bit. I don't seek the potential weak points on the NSX---unless you are racing or constantly pushing the car to or beyond it's stock limits. Perhaps some of our racing members can shed some light on this.

 

[dirtbag]

I wouldn't worry until 1950's Cessna's start falling from the sky on a regular basis. lol

 

[JD Cross]

I think the reason old Cessna's, Beavers and Otters keep flying is their metal fatigue issues are well documented, and owners replace those parts subject to fatigue failure on a preventative basis.

I doubt there are many aluminum planes from the 50's flying today that haven't had structural parts replaced due to fatigue.

A case in point is the Boeing 737. I read it was/is such a good airplane that they were in service much longer than Boeing expected and a rash of metal fatigue issues arose.
Now I think the weak points on the older jets are replaced as a matter of maintenance.

At least we won't fall out of the sky if something gives.:smile:

Jim

 

[Sumeronthechain]

No problems with my similar yeared Audi A8 and S8 with much higher miles.

 

[dirtbag]

I was being sarcastic. My point was airframes in light aircraft typically have an indefinite lifetime because they are inspected meticulously. There are a lot of vintage aircraft with more than 20,000+ hours on original airframe used for student training still in service. It's probably safe to say student aircraft are used and abused a little more than *most* of our NSX's

So until I see vintage Cessna's fall from the sky in great numbers, manufacturer or AD's imposing limits on airframe lifetime, I'm personally not going to worry.

Automotive engineers probably figure a very small percentage of cars will remain serviceable for greater than 300,000 miles anyway.

 

[JD Cross]

I've written Honda Canada hoping they will send my request for info to Jajan and one day we may get a reply. If I do get a reply I'll post it here.
Jim