Car structure weaking rate over time/mileage
Car structure weaking rate over time/mileage
(OP)
Hello,
I'm extremely curious as to your professional thoughts on how the car structure's strength and stiffness weaken over time/mileage. If we take a very basic and simplified example of, say, 2015 Honda Accord. Let's assume that initial stiffness was at 30,000 lb.ft and that the car is driven moderately - not too gently, not too harshly on average roads that are neither smooth, nor perfect. Assume standard wheels that have average 215/45 R17 wheels. Assume rust plays no role (California car)
1. What is the rate -approximately/vaguely - at which the structure would lose its strength and stiffness?
2. Would the rate of stiffness and weakness loss be faster in the beginning (first 30,000 miles) and slower thereafter? Or vise versa?
3. Is it possible that two different cars - for example 2015 Honda Accord and 2015 Mercedes E class - assuming both had the same initial structure stiffness would age differently under the same conditions?
P.S. is it possible for an automaker to build a car structure that would not groan and moan after 300,000 average miles and 20 years on the road?
Thank You very much for your insights/thoughts/suppositions on this matter
I'm extremely curious as to your professional thoughts on how the car structure's strength and stiffness weaken over time/mileage. If we take a very basic and simplified example of, say, 2015 Honda Accord. Let's assume that initial stiffness was at 30,000 lb.ft and that the car is driven moderately - not too gently, not too harshly on average roads that are neither smooth, nor perfect. Assume standard wheels that have average 215/45 R17 wheels. Assume rust plays no role (California car)
1. What is the rate -approximately/vaguely - at which the structure would lose its strength and stiffness?
2. Would the rate of stiffness and weakness loss be faster in the beginning (first 30,000 miles) and slower thereafter? Or vise versa?
3. Is it possible that two different cars - for example 2015 Honda Accord and 2015 Mercedes E class - assuming both had the same initial structure stiffness would age differently under the same conditions?
P.S. is it possible for an automaker to build a car structure that would not groan and moan after 300,000 average miles and 20 years on the road?
Thank You very much for your insights/thoughts/suppositions on this matter





RE: Car structure weaking rate over time/mileage
It's also going to vary enormously. I can tell you that where I live, the number one factor is rust. My friend's Pontiac Montana minivan needed the doors kept closed if you had to jack it up to change a wheel to stop the whole thing from simply twisting, mostly because the rocker panels weren't there any more. I doubt if the crusher in the junkyard had much trouble flattening it.
Certainly this is going to vary between models ... because some have much better corrosion protection than others.
RE: Car structure weaking rate over time/mileage
More usefully, in your PS, yes, a rough calculation suggests that a car that weighed twice as much would maintain its squeaks and rattles performance for 300000 miles. So if you can persuade enough people that they want to pay twice as much new for a car so they can drive around in an expensive, slow, heavy quiet 15 year old car, perhaps you'll find a market.
Bear in mind the luxury end seems to have gone the opposite way - a 10 year old 7 series is just an electronic timebomb, by all means buy one and enjoy the ride, but if anything goes wrong electrically you have scrap metal on your hands.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Car structure weaking rate over time/mileage
Of course, hinges and latches still wear, and weatherstrip and seals age.
Cars that start out heavier and stiffer might wearn the hinges and latches less. Or those pieces might be better to start.
Jay Maechtlen
http://www.laserpubs.com/techcomm
RE: Car structure weaking rate over time/mileage
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Car structure weaking rate over time/mileage
If spot welds are being stressed to breaking points during normal and adverse driving conditions then the structure is not designed correctly.
Breaking in crash tests is another subject.
If the body structure is correctly designed then it should never lose its stiffness, only suspension and shock absorbing rubbers etc. would wear and degrade.
So out of all the cars manufactured which ones are the best for maintaining body structural stiffness?
RE: Car structure weaking rate over time/mileage
Ever heard of statistics? The spotwelds strength will fall on a distribution, inevitably on some events a weaker weld will be on a high stress point and will break.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Car structure weaking rate over time/mileage
"Durability test" - I bet many (most?) cars in service never get used as hard as in a mfg's durability test?
Jay Maechtlen
http://www.laserpubs.com/techcomm
RE: Car structure weaking rate over time/mileage
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Car structure weaking rate over time/mileage
Or the same with cylinders falling off engines. So then auto manufacture is not into correct design of their products?
If there is a problem fix it, before it becomes the big trillion dollar recall that is a statistic to think about.
RE: Car structure weaking rate over time/mileage
There is no such thing as correct design, but anyway, how many recalls involve /structural/ issues in the bodyshell?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Car structure weaking rate over time/mileage
Actually no, there are some wonderful videos of Boeing 777/787 wings being loaded until they snap.
Matt
RE: Car structure weaking rate over time/mileage