Truths and Myths about Materials and Aerodynamics

[EarlQHan]

To everyone who came here to defend me, I thank you, I sincerely appreciate the gesture. I hope everyone understands what I'm doing here. Even if you do not buy products I develop, I want to educate people so they can demand comprehensive development from the industry. This creates a paradigm shift and means products will get better for cheaper, as they always do.

Originally Posted by u/Josh

Thanks for the post.

How do the real world fatigue properties of steel, aluminum, and titanium compare?

It depends on the specific alloy, but the commonly used materials generally have good fatigue strength. Steel and titanium alloys have a fatigue limit, meaning if they survive 10 million cycles, it will continue to do so. Aluminum has no known fatigue limit. That is why parts must be designed to stay under that stress level, for all metals. Steel will retain about 50% of its original strength when cycled, aluminum and titanium will only retain about 40%.

That is why in really high-performance applications, such as racing or aerospace, parts are mileaged and replaced at regular intervals to prevent fatigue failure. However, SubieNate is the aerospace engineer (respect) so I'm sure he could explain much better than I.

Originally Posted by SubieNate

I can almost guarantee that a large number of companies providing suspension parts are basically taking a swag (scientific wild ass guess) on the safe side of things and making the parts. Unless you're going for the ultimate in strength or stiffness:weight that often works. I'm almost positive that for a large number of companies, product testing consists of "Make it fit", install, and "Did it break after a week of street driving? No? Cool! Let's sell it!"

It's awesome that Hancha is even bothering with FEA and proper modelling of the suspension. Because the majority aren't. Are there other exceptions? Yes. Are they the norm? Not any more than Hancha is.

Cheers
Nathan

I've openly admitted I've had to use SWAG before. Without strain gauges/load cells it is impossible to know the exact loading conditions for the car. That in itself also largely depends on how much grip the car can generate, which varies widely from car to car. The LCA specifically is very difficult to model because in reality it is a pin-pin connection that acts in tension/compression, with a moment generated by damper displacement and counter moment from the anti-roll bar at the boundary condition. So using my best judgement, I had to guess what the maximum loading conditions would be, considering load transfer, then add extra load as a factor of safety, then run the analysis.

Speaking of, I will update the thread with computer modelling and real world data next.

[EarlQHan]

Originally Posted by Ro_Ja

So this post isn't totally off-topic...great info. I'm a bit of a wheel snob (okay, I'm a HUGE wheel snob), so this topic is kinda up my alley since I obsess over wheel construction techniques/processes and materials.

Then I'm sure you're aware of the "spun-forging" and "MAT" manufacturing techniques. That is a form of strain-hardening. You can see in the picture that the grains become oriented in a similar direction and also become elongated. That is why they can make those wheels lighter and stronger than some "forged" wheels. But I'll update on that later.

[Jeff@Racer X Fab]

Originally Posted by SubieNate

I can almost guarantee that a large number of companies providing suspension parts are basically taking a swag (scientific wild ass guess) on the safe side of things and making the parts. Unless you're going for the ultimate in strength or stiffness:weight that often works. I'm almost positive that for a large number of companies, product testing consists of "Make it fit", install, and "Did it break after a week of street driving? No? Cool! Let's sell it!"

It's awesome that Hancha is even bothering with FEA and proper modelling of the suspension. Because the majority aren't. Are there other exceptions? Yes. Are they the norm? Not any more than Hancha is.

Cheers
Nathan

EarlQ if you want me to remove this post, please let me know. This thread has gone way off topic from Materials/Aero.

…..Where to begin, I do my best to stay out of threads that discuss issues toward vendors but feel inclined to as Racer X Fabrication has been referenced quite a bit. I will do my best to keep this short and eliminate speculation.

Personal background, I graduated with my Engineering degree in 2007 and have been an engineer since 2003. I have a good array of experience and have worked for some of the largest companies in the world. I started Racer X Fabrication when the economy lulled and this is our 5th year in business. It has grown quite a bit from where I started it and I have continually invested in it. We do our own design work using Solidworks, and we manufacture our own parts. This allows us to be extremely competitive and in many cases lets us be light on our feet and make design changes quickly. We do not have to go through a supply chain. I choose to not share our design work publicly as I consider this IP for Racer X Fabrication. We do document every change so we can capture what was altered and updated in each design.



We choose the materials we do for specific reasons; we are fully capable of CNC machining aluminum control arms but choose not to. We run FEA, but any engineer knows this only gets you in the ball park it is a predictive analysis tool. Testing is and will be the mainstay of functional design. Currently the majority of our suspension products are being used by Tony Angelo (Professional Drifter) with his Scion FR-S. Link here: http://www.motoiq.com/magazine_articles/id/3021/pageid/6063/the-assembly-tony-angelos-scion-fr-s.aspx

I understand why Hancha / EarlQ chooses to share there FEA and design, I respect that. The reason for this post is to let members of the forum know we are not backwood mechanics (rather inferred or directed). We do a lot of design work, and the BRZ we have has been under development since the day we purchased it.

Hopefully that puts any speculation to bed, and we can all rest assured that rather its Hancha or other vendors we do a lot of work to make parts that are functional. Hopefully sell a few in the process and of course enjoy the enthusiasts that want to push their vehicles to the limit.

Thanks,
Jeff

[meeks]

real informative thread, i love it! thank you @EarlQHan

out of curiousity, what would you experts say about the composite body koenigsegg produces for their supercar (hypercar). For all the statements above, is this the 'prepreg' way or the the latter?

[ame="http://www.youtube.com/watch?v=504I_hJDFck&feature=share&list=PLHa6PXrV-yIgnXSYFT07BouKhEhyFuWnf"]Carbon Fiber Construction - Inside Koenigsegg - YouTube[/ame]

[SubieNate]

Originally Posted by racerx1715

EarlQ if you want me to remove this post, please let me know. This thread has gone way off topic from Materials/Aero.

…..Where to begin, I do my best to stay out of threads that discuss issues toward vendors but feel inclined to as Racer X Fabrication has been referenced quite a bit. I will do my best to keep this short and eliminate speculation.

Personal background, I graduated with my Engineering degree in 2007 and have been an engineer since 2003. I have a good array of experience and have worked for some of the largest companies in the world. I started Racer X Fabrication when the economy lulled and this is our 5th year in business. It has grown quite a bit from where I started it and I have continually invested in it. We do our own design work using Solidworks, and we manufacture our own parts. This allows us to be extremely competitive and in many cases lets us be light on our feet and make design changes quickly. We do not have to go through a supply chain. I choose to not share our design work publicly as I consider this IP for Racer X Fabrication. We do document every change so we can capture what was altered and updated in each design.



We choose the materials we do for specific reasons; we are fully capable of CNC machining aluminum control arms but choose not to. We run FEA, but any engineer knows this only gets you in the ball park it is a predictive analysis tool. Testing is and will be the mainstay of functional design. Currently the majority of our suspension products are being used by Tony Angelo (Professional Drifter) with his Scion FR-S. Link here: http://www.motoiq.com/magazine_articles/id/3021/pageid/6063/the-assembly-tony-angelos-scion-fr-s.aspx

I understand why Hancha / EarlQ chooses to share there FEA and design, I respect that. The reason for this post is to let members of the forum know we are not backwood mechanics (rather inferred or directed). We do a lot of design work, and the BRZ we have has been under development since the day we purchased it.

Hopefully that puts any speculation to bed, and we can all rest assured that rather its Hancha or other vendors we do a lot of work to make parts that are functional. Hopefully sell a few in the process and of course enjoy the enthusiasts that want to push their vehicles to the limit.

Thanks,
Jeff

Jeff, just to be clear, my post was in no way directed at you or Racer X fabrication. In fact, I think Gem is the only one in the thread talking about you. From what I've seen, you would be on the list of exceptions I mentioned. My post was mainly aimed towards the flood of parts being made for this car by an unheard of number of companies with no real background or proof of design, craftsmanship, or quality.

@EarlQHan pretty much has the fatigue stuff down. I'm not a metals expert at all (I deal almost exclusively with composites at work) but it's my understanding that steel, if kept under a certain stress/strain threshold, will have basically an indefinite fatigue life. Aluminum on the other hand, will fatigue at any stress level. At a certain point, it will fail. If you design properly, this fatigue life will be in the millions and millions of cycles and in real life will never become an issue. I haven't studied Titanium at all so I won't speak to that.

An interesting tidbit I do know, is that the main frame that the engines mount to in an F-18 is normally made of of aluminum, and a huge part of the operating costs the US military incurs on them is replacing those when their service life is up. Switzerland didn't want to deal with this, as it required shipping or flying the craft back to the US, having considerable downtime, and then sending them back across the world. They ordered theirs with the rear main frame element made in titanium. According to the guy I spoke with at Northrop they expected them to last basically forever.
@meeks-the Koenigsegg is definitely made out of prepreg. A lot of the pictures and video I've seen of their manufacturing process reminded me very much of my internships with a major aerospace company. I would love to go work for them. Unfortunately I don't speak Swedish.

Cheers
Nathan

[EarlQHan]

EDIT: Jeff, I do not mind one bit. Please keep up the good work.

updated with computer modelling information.

updated with forging vs. casting and wheel manufacturing techniques.

[ft_sjo]

The main concern I have is how well these aftermarket products will work in the event of a crash. Most of us are not purely using our cars for track usage. People can design parts which on the computer say will work fine during normal use, or even 10x the normal use, but will they break when someone t-bones you?

In which case i'd prefer a steel arm that bends but keeps stuff in the right sort of place, over an aluminium arm which will break.

I don't think many/any aftermarket part manufacturers do any kind of crash testing, which is understandable as the parts wouldn't be affordable otherwise!

[EarlQHan]

Originally Posted by ft_sjo

The main concern I have is how well these aftermarket products will work in the event of a crash. Most of us are not purely using our cars for track usage. People can design parts which on the computer say will work fine during normal use, or even 10x the normal use, but will they break when someone t-bones you?

In which case i'd prefer a steel arm that bends but keeps stuff in the right sort of place, over an aluminium arm which will break.

I don't think many/any aftermarket part manufacturers do any kind of crash testing, which is understandable as the parts wouldn't be affordable otherwise!

You raise a valid point. But tensile strength is tensile strength. Doesn't matter if it's steel or aluminum. A steel part is not necessarily stronger or safer than aluminum, or vice-versa. It's all in how it's designed and manufactured. If it's designed properly, that is all taken into consideration. Remember the point I made about unintended use? Even though parts say "off-road use only" a good engineer should realize people will still drive the car on the street with the product on the car. With that in mind, a good engineer will think of crash/worst case scenarios.

That is why I, personally, FEA the product with 2G braking, 2G cornering, 2G bump for worst-case scenario at the track. Then I do 4G bump (pothole) and 10G buckling (crash). 10G is likely excessive, because at that point (the way I analyzed the part) that's 75000 lbs or 33 kN directly on the part alone, without considering how energy is dispersed through the rest of the car. Depending on the energy of impact, that kind of force could be fatal to the driver, whether the part stays intact or not. I don't know how other engineers do it, so I cannot speak for them.

Like driving, it's the nut behind the keyboard that needs to be tightened down first.

[ft_sjo]

Is that 10G figure an industry standard, from professionals are are used to doing crash tests etc.?

[OrbitalEllipses]

Your knowledge, give it to me.

[EarlQHan]

Originally Posted by ft_sjo

Is that 10G figure an industry standard, from professionals are are used to doing crash tests etc.?

AFAIK, industry standard for crash tests in the US are done at 40 MPH. How many G's that will be is dependent on mass and deceleration rate. However, at a 40 MPH crash, the driver usually remains conscious, meaning that the crash is under 6 G's. Over that the driver will become unconscious (without a flight suit), which is why I arbitrarily picked 10G's. This is an example of SWAG and using math to get the numbers.

Originally Posted by OrbitalEllipses

Your knowledge, give it to me.

Here, take it. Did you get it? Good

[EarlQHan]

http://www.ft86club.com/forums/showp...1&postcount=13

[s2d4]

Originally Posted by EarlQHan

like driving, it's the nut behind the keyboard that needs to be tightened down first.

Unfortunately some nuts somehow comes back into use after being discarded, so the people that decided to use the nut again needs to have their own nuts replaced as well.

[CA2]

Carbon fiber composites will act differently than metals in a crash. They fail differently. They respond to damage differently.

Also, composite structures are difficult to accurately model. Is any sort of model verification being done (ie. testing w/ strain gages, etc.) on these parts? To have any real confidence and to eventually establish design allowables, you should have some sort of iterative process of analysis, test, tweak model, repeat.