chassis frame profile

[gr3pz]

dear all,

which is the best profile for chassis tube? square, rectangular, or square profile?

best regards,

gr3pz

[gr3pz]

dear all,

which is the best profile for chassis tube? square, rectangular, or square profile?

best regards,

gr3pz

[markocosic]

Circular... http://fsae.com/groupee_common/emoticons/icon_wink.gif

Square is far easier to work with, but hollow circular sections make best use of the material.

[ben]

Not necessarily. In a spaceframe the loads aren't always in pure tension/compression no matter how well you design things. In this case a square or rectangular tube can offer a stiffer joint.

Damian Harty of Prodrive explained this to me when we judged together at FStudent. He also pointed it out to a number of teams. He suggested doing a simple solid or shell FE analysis of a T junction between circular and square tubes and look at the stiffness of the joint.

Ben

[gr3pz]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ben:
Not necessarily. In a spaceframe the loads aren't always in pure tension/compression no matter how well you design things. In this case a square or rectangular tube can offer a stiffer joint.

Damian Harty of Prodrive explained this to me when we judged together at FStudent. He also pointed it out to a number of teams. He suggested doing a simple solid or shell FE analysis of a T junction between circular and square tubes and look at the stiffness of the joint.

Ben </div></BLOCKQUOTE>

Which one is the stiffer? I do some shear stress calculation of different profile caused by torque loads, and the result is square hollow profile has the lowest shear stress, follow by circular, and rectangular hollow profile. Can you give me detail data about the advantages of these profiles?

Regards,

gr3pz

[markocosic]

Interesting tip Ben; noted. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[ben]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by gr3pz:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ben:
Not necessarily. In a spaceframe the loads aren't always in pure tension/compression no matter how well you design things. In this case a square or rectangular tube can offer a stiffer joint.

Damian Harty of Prodrive explained this to me when we judged together at FStudent. He also pointed it out to a number of teams. He suggested doing a simple solid or shell FE analysis of a T junction between circular and square tubes and look at the stiffness of the joint.

Ben </div></BLOCKQUOTE>

Which one is the stiffer? I do some shear stress calculation of different profile caused by torque loads, and the result is square hollow profile has the lowest shear stress, follow by circular, and rectangular hollow profile. Can you give me detail data about the advantages of these profiles?

Regards,

gr3pz </div></BLOCKQUOTE>

I haven't actually done the analysis yet. Since I'm embarking on a non-FSAE race car design in the coming weeks it will likely get done soon.

Ben

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by gr3pz:
Which one is the stiffer? I do some shear stress calculation of different profile caused by torque loads, and the result is square hollow profile has the lowest shear stress, follow by circular, and rectangular hollow profile. Can you give me detail data about the advantages of these profiles?

Regards,

gr3pz </div></BLOCKQUOTE>

If you are talking about twisting of the tube ("shear stress ... torque loads"), then for a given wall thickness and perimeter (ie. same mass/length of tube) the circular profile is stiffest and has least stresses, followed by square, with rectangular least efficient. The rectangular profile has greatest stresses in the middle of its long side.

Note: For same wall thickness, ~25mm diameter circular has same mass/length as ~20mm square.

Again for same mass/length, I would guess that an optimally designed joint would be stiffest with circular tubes. But for "optimally designed" (don't you love that word Ben http://fsae.com/groupee_common/emoticons/icon_wink.gif) the joint might need internal webs. Webs aren't hard to do, but perhaps best left for only the most critical joints.

Cutting the ends of square or rectangular tubes is fairly easy for "box" shaped structures (ie. flat panels and 90 degree corners). But you might still have to do four cuts per tube end - think about mating up to the corner radius... Square and rectangular tubes can be a nightmare, and look ugly http://fsae.com/groupee_common/emoticons/icon_frown.gif, when you have a lot of compound angles.

Z

[ben]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
(don't you love that word Ben http://fsae.com/groupee_common/emoticons/icon_wink.gif)

Z </div></BLOCKQUOTE>

Hell yeah!!

BTW I discovered fairly quickly while judging this year that the quality of design reports tends to be inversely proportional to the number of instances of (and variations on) the word "optimised"

Ben