Aren't we talking about the relationship between the amount the sway bar deflects given a particular load. The stress - strain relationship of a material is the modulus of elasticity NOT the yield strength or hardness. I believe Cristo is correct, the aluminum sway bar of the same cross section would deflect more (less stiff) than a steel alloy bar given the same applied load...just one opinion...

 

couldn't find that info easily, but the numbers should follow a parallel path.

 

Kurzbeschreibung:
Für den Mazda®® MX-5 haben wir ein Stabilisatorenkit für Vorder- und Hinterachse aus ultraleichtem Aluminium entwickelt, das selbst härtesten TÜV-Prüfungen standhält. So sind die aus AL7050 gefertigten Stabilisatoren bei 40 % weniger Gewicht ca. 35 % fester als die Originalen. Die Alu-Stabilisatoren werden mit TÜV-Gutachten geliefert. Im Lieferumfang enthalten sind Polybushes (Gummilagerungen) in gehärteter Ausführung sowie neue stabilere Bügel zur Befestigung der Gummis. Auf den Fotos sehen Sie die hinsichtlich der dynamischen Betriebsfestigkeit durchgeführten TÜV-Tests. Bei diesen Tests wurden die Streben 1.000.000 Mal verbogen ohne jegliche Festigkeit zu verlieren. Damit bringen wir erstmalig ein Stabilisatorenkit aus Aluminium mit einer TÜV-Zulassung auf den deutschen Markt. Wir haben uns bereits von den exzellenten Fahreigenschaften überzeugt und möchten Ihnen diese natürlich nicht vorenthalten.

Die zul. Achslasten der Stabilisatoren sind:
VA 680 Kg; HA 705 Kg

Die Durchmesser der Stabilisatoren sind:
22mm für den Vorderen
15mm für den hinteren

 

Short description: For the Mazda MX-5 ® ® we have developed a stabilizer kit for front and rear axle of ultra-light aluminum that can withstand even the harshest TÜV tests. Thus, the stabilizers are made of AL7050 at 40% less weight about 35% stronger than the originals. The aluminum stabilizers are supplied with TÜV parts certificate. The package includes Polybushes (rubber bearings) in hardened versions and new stable bracket for attachment of the gums. In the photos you see carried out in terms of the dynamic fatigue tests TUV. In these tests, the struts were bent 1,000,000 times without losing strength. Thus we get the first time a stabilizer kit in aluminum with a TÜV-approval on the German market. We have already discovered the excellent ride and they do not want to deprive you. The permissible axle loads of the stabilizers are: VA 680 Kg, 705 Kg HA The diameters of the stabilizers are: 22mm for the Middle 15mm for the rear

 

"Thus, the stabilizers are made of AL7050 at 40% less weight about 35% stronger than the originals. "

I'm guessing they are talking about the original steel bars compared to the aluminum ones?

 

Data for 7068 alloy:

This source says E (Young's modulus of elasticity) is 10,600,000 or 10,700,00 psi
http://www.kaiseraluminum.com/wp-con...8-brochure.pdf

A very tough, strong, and hard alloy, but only a little springier than most aluminum alloys
(or should we say aluminium to pay homage to the british nature of our MINIs).

A36 steel is 29,000,000 psi.

Getting back to the earlier question, each of these would have the same anti-sway stiffness
(ignoring the way the ends of the bar are different from the middle to supply an attachment point):

a 19mm solid steel bar weighing 11.28#
a 22mm hollow steel bar with 2mm wall thickness weighing 5#
a 24.4mm solid forged 7068 aluminum alloy bar weighing 6.7# - (0.36 x the density of steel - 2.81/7.8)

I dare you to try to make a forged hollow aluminum sway bar.

 

 

With all due respect, unless the posters have a background in engineering or material science, I think the insistence that this issue has anything to do with yield strength, hardness, or strength to to weight ratios just demonstrates a lack of understanding of what is important in a device of this type. Perhaps the link below will help the posters understand as Cristo points out it is an issue of "springiness". The aluminum alloy with a lesser modulus of elasticity will deflect more with the same load as the steel...see link:

http://www.instron.us/wa/glossary/Mo...com/search/web

 

However I have a plate of 5/16" 7000 series aluminum I bought from a guy that worked for Alcoa. I used it for some motorcycle motor mounts . I had a scrap piece about a 1/2' wide and compared it to a piece of mild steel about the same width. I set both pcs in a vise one a time and I devised a torque wrench to measure the deflection before a permanent bend. The aluminum was by far much stiffer and resisted being bent much more.

 

JPMM: The point of permanent deformation is the "yield" of the material, what is important is the stress-strain relationship (approximately linear) prior to permanent deformation. The slope of that line is the "modulus of elasticity" of the material. Elasticity means once deflected it comes back to the same place. I don't think we want our sway bars to permanently deform, so yield strength isn't important to the design.