what i do know

is I like grape jelly

we're going to get yelled at for talking about jelly in a RRO A-Arm thread



ok i think everything got covered from the JBA discussion so let's shush till new info on the RRO arms shows up



Thanks for the clarifications Boiler and anyone else that assisted in getting things out on the table

Gee, you're giving up without even mentioning peanutbutter?

I like peanut butter on my pancakes

taco bell hot sauce on PANCAKES???? ewww

From what I am reading it sounds like you are all sort of right depending on the size of materials used. So answer me these 2 questions.

If the cross sectional area of material in a tube is the same as the cross sectional area of a solid made of the same material does this mean they are also the same bending strength or is the tube stronger because it has '4' sides.

If the cross sectional area of the tube is less than the solid does this mean the tube is weaker in bending strength?

So..... if they're all done talking about food now nosnorb - were you able to get those arms on this weekend yet? How did the install go? run into any problems with fitment or such?

The areas being the same does not mean the same strength. if they have the same cross sectional area, the tube will be stronger (in bending), since it will have a larger outer diameter. And it is entirely possible to have a tube with less cross sectional area that is actually stronger than a solid bar. it is all dependent on the geometry of the cross section.

If you have one tube and one round bar, both are made of the same material and both are the same outside diameter, the solid round bar will be stronger. Here is an example of a four foot long bar/tube loaded in the middle of the span.

Proof:

TUBE:
Material Properties: (From www.matweb.com)
Material: 1020 Steel Cold Rolled
Yield Stress (Yield): 50,800 psi
Density: 0.284 lb/in^3 (pounds per cubic inch)
Elasticity Modulus: 29,700,000 psi

Geometry:
Tube OD (OD): 2.00 in
Wall Thickness: 0.375 in
Tube ID (ID): =OD-(2*Wall Thickness) = 1.25 in
Tube Length (L): 48 in

Section Properties:
Max Distance from Neutral Axis (c): =(OD/2) = 1 in
Cross-sectional area: =(pi/4)*(OD^2 - ID^2) = 1.91441 in^2
Second Moment (I): =(pi/64)*(OD^4 - ID^4) = 0.66556 in^4
Section Modulus (Z): = (I/c) = 0.66556 in^3
Force to reach yield stress (F1): =(4*Yield*Z)/L = 2817.52 lbf (pound-force)
Deflection at max stress (ymax): = ((F1)L^3)/(48*E*I) = 0.3284 in

SOLID BAR:
Material Properties: (From www.matweb.com)
Material: 1020 Steel Cold Rolled
Yield Stress (Yield): 50,800 psi
Density: 0.284 lb/in^3 (pounds per cubic inch)
Elasticity Modulus: 29,700,000 psi

Geometry:
Tube OD (OD): 2.00 in
Wall Thickness: 1.00 in
Tube ID (ID): =OD-(2*Wall Thickness) = 0.00 in
Tube Length (L): 48 in

Section Properties:
Max Distance from Neutral Axis (c): =(OD/2) = 1 in
Cross-sectional area: =(pi/4)*(OD^2 - ID^2) = 3.14159 in^2
Second Moment (I): =(pi/64)*(OD^4 - ID^4) = 0.78540 in^4
Section Modulus (Z): = (I/c) = 0.78540 in^3
Force to reach yield stress (F1): =(4*Yield*Z)/L = 3324.85 lbf (pound-force)
Deflection at max stress (ymax): = ((F1)L^3)/(48*E*I) = 0.3284 in

Note that both the solid bar and the tube require the same displacement to reach yield stress, but the solid bar will take a higher load to reach that displacement.

A 2" solid bar over a 2.00 x 0.375" tube will take an 18% higher load to reach yield stress and will weight 64% more. It's not worth the strength to weight trade-off.... unless you're getting it for free.

The areas being the same does not mean the same strength. if they have the same cross sectional area, the tube will be stronger (in bending), since it will have a larger outer diameter. And it is entirely possible to have a tube with less cross sectional area that is actually stronger than a solid bar. it is all dependent on the geometry of the cross section.