I want to build a Cage

How much weight could you save by using a sparser/thinner walled tube made out of CroMo rather than "regular" steel tubing? I.e. you wouldn't need as much bracing with a stronger tube, right? Or is CroMo not significantly enough stronger to make much difference? I don't know about cost... I'm just thinking out loud....

I'd like to put a cage in my truck sooner rather than later - but I don't want the weight or braces intruding on the interior space - which makes a cage troublesome, of course.
 
its going to be a hell of a chart with strength being dependant and BOTH dia. and wall thickness being independent factors. I could make one based on maximum stress as the strength indicator. you would want one for bending and one for tension/compression. and then one for the principal stress when both loading conditions are satisfied.
 
jjvande said:
its going to be a hell of a chart with strength being dependant and BOTH dia. and wall thickness being independent factors. I could make one based on maximum stress as the strength indicator. you would want one for bending and one for tension/compression. and then one for the principal stress when both loading conditions are satisfied.
Click to expand...
I don't have the resources to come up with such a chart. If you could show the bending and tensile strengths of all the common roll cage size tubing that would be awesome and hopefully not too many.

diameters-
1.5
1.75
2.0

walls-
.095
.120

materials-
HREW
DOM
Chromo
 
BrettM said:
I don't have the resources to come up with such a chart. If you could show the bending and tensile strengths of all the common roll cage size tubing that would be awesome and hopefully not too many.

diameters-
1.5
1.75
2.0

walls-
.095
.120

materials-
HREW
DOM
Chromo
Click to expand...
Yea i could do it. Itl have to wait till sun night, or mon. They will be 3-D plots with x,y axis being diameter and thickness, and z being relative strength. If we normalize the strengths, making the lowest "1", then they are easy to compare and we dont have to worry about actual stress values. assuming we use the same loading conditions/equations for each case.

The difference in material will be factored in as a scale based on yield strengths of the different materials. so if one were to compare two different geometries of two different materials, they could multiply the geometrical strength value by the material yield strength scale to get the comparison. eg, tube A is twice as strong as tube B based on like materials via the chart. then if you wanted to compare tube A to tube B of a stronger material, you would multiply the strength of tube B by a factor/scale. If material B has twice the yield strength of material A, then tubes A and B could be equal in strength (2x1=2=2). Tube B sees twice the stress levels as tube A, but the higher yield strength of the alloy allows it to withstand the elevated stress levels resulting from the different cross-sectional geometries.

not sure if that makes sense,but ill give it a shot and make sure it all works out all fine and dandy.:)

cheers.
 
Did I miss something or did 1990XJ4x4 say CroMo and Mig welding? The last I checked when you weld CroMo you had to pre-heat, Tig weld then post heat. If welding CroMo changed please let us know.

Guy
 
Did I miss something or did 1990XJ4x4 say CroMo and Mig welding? The last I checked when you weld CroMo you had to pre-heat, Tig weld then post heat. If welding CroMo changed please let us know.
Click to expand...

Yes I did mention both of those things but if you read it again I said my experience welding tube was TIG on chromo, but I was going to be using a MIG on my cage that was not going to be made of Chromo.
 
1990XJ4x4 said:
Yes I did mention both of those things but if you read it again I said my experience welding tube was TIG on chromo, but I was going to be using a MIG on my cage that was not going to be made of Chromo.
Click to expand...



Now I understand :wave: .

Guy
 
BrettM said:
no, this IS so. strength is gained by larger diameter. strength is lost by thinner wall. there is a point where the two meet and one passes the other.

I don't know where that exact point is, but to choose some safe numbers; I would wager that 2.5" .095 wall would be stronger in tension/compression and bending than would 1.5" .120 wall of the same steel.
Click to expand...

The wall thickness(cross section area) and the radius of the tubing are used to derive the moment of inertia of the tubing. The ability of the tubing to resist bending and buckling loads is a function of the moment of inertia.
The chart below lists the calculated moment of inertia (I) for several common sizes of roll cage tubing.

1.500 X .095 - 0.104
1.500 X .120 - 0.125
1.625 X .095 - 0.134
1.625 X .120 - 0.162
1.750 X .095 - 0.170
1.750 X .120 - 0.205
2.000 X .095 - 0.259
2.000 X .120 - 0.314

I for 1.75" X .095 tubing = .170 vs .125 for the 1.5" X .120 tubing indicates that BrettM's 2.5" X .095 wager is a pretty safe bet.

As mentioned before, wall thickness takes on additional importance in an exo-cage where localized impact strength is important.
 
Taking those values of Inertia and calculating bending stress...

the 1.75x.095" is 16.5% stronger in bending than the 1.5x.120" (Stress=Mc/I)

however, it is 5% weaker in tension/compression loading based on cross-sectional area. (Stress=Force/area)

1.75x.095 is also 5% lighter weight.
 
jjvande said:
Taking those values of Inertia and calculating bending stress...

the 1.75x.095" is 16.5% stronger in bending than the 1.5x.120" (Stress=Mc/I)

however, it is 5% weaker in tension/compression loading based on cross-sectional area. (Stress=Force/area)

1.75x.095 is also 5% lighter weight.
Click to expand...

depending on the length of a given section of tubing, it may succomb to buckling before the tension/compression limit is reached.
 
So what's wrong with pocket protectors??????
 
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