JeffTsai

iTrader: (1)

Just wondering why do some manufacturers make these braces out of aluminum. It's a much weaker material than steel. The only reason I can think of is the weight saving, but for a bracing component shouldn't it be as strong and stiff as possible?

Here's the list I know off the top of my head.
TRD Front chassis brace: Steel
Tom's F/R braces: Steel
Cusco Front chassis brace: Aluminum

LexFather

Aluminum won't bend at all even while taking the hard Gs of a corner. Yes its for weight savings... The Acura NSX is built out of Aluminum as well as the new Jag XJ and XK Aluminum is EXPENSIVE for cars, that is why you don't see more use of it.

JeffTsai

iTrader: (1)

So you're saying the Cusco front lower brace made out of aluminum would be a better choice than the TRD bar? It seems like the TRD bar is MUCH beefier and probably also heavier. Either way I'm leaning towards the Cusco bar because its blue but I was just wondering about the structural weakness since the construction material is aluminum. Unless they are using a high strengh alloy such as 7075, but thats also very expensive just for the material itself. Or if the stress is only push/pull(tensile?) vs torsional stress then maybe a tubular aluminum at the right shape/angle can withstand some pretty high stress levels.

I'm probably just rambling here...but can any material/mechanical/structural engineers chime in? I'm an EE in progress(school) so this isn't exactly my field

engin_ear

iTrader: (1)

Aluminum is WEAKER than steel. It can get strength from properly shaping an extrusion. Various alloys will impart strength to the aluminum, but there is still a tradeoff of weight savings vs strength. (This especially applies when you're talking about bicycle frames.) Steel can be a strong as a tank, especially steel alloys, but your car may weigh as much as a tank too.
Not to be compared with titanium, which is both stronger and lighter than steel.

macd7919

iTrader: (10)

Up to yield strength aluminum is actually a little more tolerant than steel for example, widely used grades of both:

6061- T6 Aluminum:

Yield Strength:
Tensile = 37 ksi
Comp. = 37ksi
Weight = .098 lb/in^3

Ultimate Strength:
Tensile = 42ksi
Comp. = 42ksi

A36 Steel:

Yield:
Tensile = 36ksi
Comp. = 36ksi
Weight = .294 lb/in^3

Ultimate:
Tensile = 58ksi
Comp = 58ksi

So up to a point, before permanent deformation, aluminum is actually "stronger(for lack of a better term)" than steel. By stronger it would resist more force without being perm. altereted (i.e bent). Ultimate strength of steel though is much higher, so if you are worried about snapping your strut bar in half then you would want steel. Honestly I would agree it would come down to design, to honestly find which one is better you would need to know the forces at the shock towers etc.. and work it out. Weight on the other hand, 6061 is almost 1/3 the weight of steel Also, even if the aluminum did "bend" under heavy forces (ie. cornering hard) it would still provide an increase in chassis stiffness. The addition of a strut bar perios is going to require more force to twist/bend than driving without one. Granted steel may provide more resistence to the twisting or bending but the key is how much force is present, If you only have x amount of force and aluminum can handle it, then why bother with steel. If you have xx force and aluminum can handle without breaking but is still going to to temporarily deflect (deform) then steel maybe a consideration and would have to be based up on weight issues. The real key here would be knowing how much force is being generated along the horizontal axis under cornering.

JeffTsai

iTrader: (1)

Well, the 6061 aluminum reaches the ultimate strength a lot sooner than steel. So that probably means that the aluminum flexes a lot more than steel once the stress on both start to pass their respective tensile strengths. Hm on a third note, I wonder if Ferrari's and Lambo's come with titanium braces...

Either way though, I don't think the car chassis flexes nearly enough for the aluminum brace to even be anywhere close to the limit. I've seen a few wrecked cars with the strut brace only slightly bent so I guess under normal operation the aluminum is more than adequate.

engin_ear

iTrader: (1)

You've justified the fact that an aluminum bar will bend, but return to shape. A slight deformation of an aluminum bar under loads greater than its ultimate strength will not even be detectable at a glance, so will go unnoticed. Of the 2, I'd much rather have a steel bar. The weight difference isn't enough to get excited about, and it is sprung weight, not unsprung. The purpose of the bar is to prevent deflection by forming a rigid connection. While you're right about the loads presented to the bar not necessarily being significant, I'd rather not have to go out and measure the forces, and just go with a steel bar.

The TRD bar is the strongest one I know of - that thing is like a tank. It pained me to get rid of mine to accommodate the Tein EDFC motors. Now I have the Chrome CarsonTuned one, which is also steel. BTW, I had first ordered the polished aluminum one --- but IT BENT IN THE SHIPPING BOX before it got to me....no thanks.