Anyone know what aluminium alloy is used to make booms?
I did find an advert for North that says they use 7075 ( and claimed its 30% stiffer than the aluminium used in other makes , which is nuts).
Seems manufacturers use the T8,T9 designation as a promise of stiffness, which is wrong.

Aluminium has a Youngs modulus of generally = 69 GPa. This is a measure of stiffness. It can't be changed - it is an inherent property of the material. Some aluminium alloys can be slightly higher eg 7075 maybe 72GPa.
For aluminium the T designation is to do with strength, which is the amount of force it can withstand and still retain its original shape.
The geometry of the boom will have a lot to do with some feeling stiffer than others, also the cross section shape of the tubing.
Interesting that the manufacturers don't tell us the grade of aluminium they use. Maybe its their trade secret. The T8 T9etc is meaningless.

Dont confuse stiffness with strength. Stiffness is how much it deflects for a given force. Strength is how much force it takes to break it. Annealing or heat treating has no effect on stiffness but a massive effect on strength. Architectural grade 6063 and aircraft grade 7075 have the same stiffness (for practical puposes)But heat treated 7075 may be many times stronger than 6063. Common boom grades might be 6061t6 or 7075t6 or proprietary variations of them that could be given any old name or number. Higher t numbers dont mean higher strengths, the just mean different kinds of heat treatment which can include heating, aging, quenching and even cryogenic cold treatment. H numbers generally mean cold work. Changes in alloy composition mostly affect stiffness by only a few percent but do have massive effects on strength and the way it is heat treated. All generalisations that engineers will argue over, but for the real world, thats the low down.

So a boom made from T0 would not bend any more than a boom made from T9? ie T9 is stronger, but not stiffer?

Well I am still lost as the numbers posted about show that for increasing temper, the tensile strength goes up
surely that makes a boom stiffer and stronger.

Higher temper = higher tensile strength (higher Youngs modulus) and thus a stiffer boom (for the same construction) ??

So T3 or T8 is not meaningless???

And 7075 is stronger than other aluminiums.

Higher grade aluminium has a higher yield point. That means it can take higher stress loads before it starts deforming plastically.

Temper designation[edit]The temper designation follows the cast or wrought designation number with a dash, a letter, and potentially a one to three digit number, e.g. 6061-T6. The definitions for the tempers are:[5][6]-F As fabricated-H Strain hardened (cold worked) with or without thermal treatment-H1 Strain hardened without thermal treatment-H2 Strain hardened and partially annealed-H3 Strain hardened and stabilized by low temperature heatingSecond digit A second digit denotes the degree of hardness-HX2 = 1/4 hard-HX4 = 1/2 hard-HX6 = 3/4 hard-HX8 = full hard-HX9 = extra hard-O Full soft (annealed)-T Heat treated to produce stable tempers-T1 Cooled from hot working and naturally aged (at room temperature)-T2 Cooled from hot working, cold-worked, and naturally aged-T3 Solution heat treated and cold worked-T4 Solution heat treated and naturally aged-T5 Cooled from hot working and artificially aged (at elevated temperature)-T51 Stress relieved by stretching-T510 No further straightening after stretching-T511 Minor straightening after stretching-T52 Stress relieved by thermal treatment-T6 Solution heat treated and artificially aged-T7 Solution heat treated and stabilized-T8 Solution heat treated, cold worked, and artificially aged-T9 Solution heat treated, artificially aged, and cold worked-T10 Cooled from hot working, cold-worked, and artificially aged-W Solution heat treated only.

The material properties of aluminium alloy are depicted by the following designation XXXX - XX. The first 4 numbers depict the alloy content and the last 2 numbers depict the temper.

Strength is the ability to withstand load. This is measured as either Yield Strength (the maximum load before the aluminium will elastically deform - i.e. return to its original shape after removal of the load) or Ultimate Strength (the maximum load before failure). Differnet grades and temper of alumoinium have different strengths eg:

6061 - T6: Ultimate tensile strength 310MPa, Yield Strength 270MPa
7075 - T6: Ultimate tensile strength 560MPa, Yield Strength 460MPa

Stiffness is resistance to deflection under load. This is measured by Youngs Modulus. As Piv has already said, this does not markedly change for different grades and temper of aluminium alloys eg 6061-T6 has a Youngs Modulus of 69 and 7075 - T6 has a Youngs Modulus of 72 (less than 5% difference)

Hence for boom of the same design - ie length and tube cross section, made from 6061 - T6 or 7075 - T6, then the 7075 - T6 boom:
- will be 4.3% stiffer (i.e. will deflect 4.3% less) under the same load
- will withstand a 70% bigger load before it plastically deforms and
- will withstand a 80% bigger load before it breaks

Macro is also right in that the section size properties of the tube also effect strength and stiffness

Note that even the lowest grade Carbon Fibre Reinforced Polymers have at over twice the Youngs Modulus (i.e. stiffness) and nearly 3 times the ultimate tensile strength as 7075 - T6, hence why carbon fibre booms are worth the extra money

Mark,

The following comparative Load Deflection Curves for Carbon fibre, 6061-T6, and 7075-T6 might help explain.

Stiffness and strength are not the same thing.

Stiffness is the resistance to deflection under load - eg. how much your boom flexes as you sail. From the curves below, under the same load, carbon fibre deflects much less than 7075 - T6 and 7075 - T6 only deflects a little bit less than 6061 - T6. I.e. the steeper the straight section of the curve the stiffer the material (this is the Youngs Modulus)

However strength is how much load can be resisted before it yields or breaks - eg. how much shock loading your boom can handle in a shore dump. From the curves below carbon firbre is much stronger than 7075 and 7075 is much stronger then 6061.

Hope this helps

Mark, Tempering doesn't make a boom bend less for a given load. Tempering an alloy boom means its can endure a bigger load and deflection before the boom fails

Macroscien said..
At this stage the whole strength of the boom or mast is entirely dependent on the walls.
Will be interesting to see one day newly designed boom or mast build around honeycomb core.
Some of the forces then will be transferred internally troughs that structure inside.For Hi tech mast we could also imagine masts being pressurized that beside lowering overall weight, increased performance may offer change in stiffness on demand, depending on pressure inside....

If you pressurise any vessel, it gets heavier... because there are more molecules in it per volume. Do you have special science up your sleave ?

[ assuming no helium, but using that would eventually leak through the walls ].

Another advantage with carbon is it is easier to change diameter and wall thickness than with aluminium. So my enigma race boom has nice big tubewhere you dont hang onto it and nice skinny tube where you do. Plus carbon laminate is lower density than aluminium, so a given thickness of carbon is lighter than aluminium. Enjoy the carbon.

^^^ Stop trying to invent kiting.

Look what happened last time

Will this follow on and open up a can of worms on Carbon Booms materials now ?


Interesting read, thanks & keep it up fellas.

gofaster said..
Right, going back to my original question, if the manufacturers don't specify the alloy they are using and just bull**** with the T8 etc, then its not possible to compare their offerings on material properties. Plus the shape of the boom and cross section of the tubing has a major effect on the stiffness of the boom.

It would be necessary to compare booms with some sort of standard load test. Probably never going to happen(although IMCS has happened for masts)

If I can't go carbon, from peoples' experience, what is the best AL boom out there, in terms of attachment to the mast, stiffness and strength? around 180 length, freeride

7075. Those who are using it, do specify.
Tecnolimitz Ergal are regarded as best. But then u are paying $600 insteads of $300 for a boom that is still ali
For that you can easily find secondhand carbon, so it becomes a hard decision huh

John340 said..
Mark,

The following comparative Load Deflection Curves for Carbon fibre, 6061-T6, and 7075-T6 might help explain.

Stiffness and strength are not the same thing.

Stiffness is the resistance to deflection under load - eg. how much your boom flexes as you sail. From the curves below, under the same load, carbon fibre deflects much less than 7075 - T6 and 7075 - T6 only deflects a little bit less than 6061 - T6. I.e. the steeper the straight section of the curve the stiffer the material (this is the Youngs Modulus)

However strength is how much load can be resisted before it yields or breaks - eg. how much shock loading your boom can handle in a shore dump. From the curves below carbon firbre is much stronger than 7075 and 7075 is much stronger then 6061.

Hope this helps

Hmmm. Why is deflection shown on the x-axis (usually the independant variable), and the load on the y-axis (the dependant variable)? Ordinarily, wouldn't load be the independent variable? Is it so you get a saggy bit in your curve as the alloy itself goes saggy? Wouldn't look as pretty if it curved back towards your y-axis.

Just asking by the way.