Wire Rope Stretch/Elongation 1

[TCPhoenix]

I am trying to calculate the elongation of wire rope as a fuction of load. I understand that it will be based on the wire rope configuration, overall diam, number of strands and number of wires. Is there a formual out there for this?

 

[byrdj]

I googled this site

http://www.spaceagecontrol.com/calcstre.htm

 

[arto]

Shigley's Machine Design has a good section on Wire rope design

 

[40818]

If i read your post correctly then your wire has an axial load applied to it??
If this is the case then its simply back to basics:

E = (stress/strain), then just rearrange for elongation.

 

[CanuckMiner]

TCPhoenix,

In my industry (underground mining), rope stretch on the hoist ropes is a big deal. I think you are asking about the elastic stretch (as opposed to the constructional or permanent stretch that would be induced in the rope and is never "recovered").

Rope Stretch = P x L / (A x E)
Where P is payload or force in pounds
L is length of rope in feet
A is nominal cross sectional area (e.g. a 1 in diameter rope has an area of 0.785 sq in)
E is the modulus of the rope in psi

The E varies depending on rope construction. A few examples (from Wire Rope Industries):
Round Strand Rope
6x7 fibre core - 9 Mpsi
6x7 steel core - 10 Mpsi
6x19 fibre - 8.5 Mpsi
6x19 steel core - 9.4 Mpsi
8x19 fibre core - 5.3 Mpsi
non rotating rope, fibre core - 7.8 Mpsi

Flattened Strand Rope
6x8 fibre core - 10.5 Mpsi
6x27 fibre core - 10 Mpsi
non rotating rope - 8.5 Mpsi

Hope this helps.

Cheers,
CanuckMiner

 

[40818]

As i said, just go back to basics!

 

[JsTyLz]

The equation is not as simple as y=mx+b. It actually would have to be calculated piece wise. One section would be the section where the woven strands' geometry has the most effect, then a certain load is reached where the mechanical properties of the wire materials start to have more of an effect.

Check machinery hand book also.

 

[40818]

Sorry, but the whole basic assumption of linear stress analysis is based upon hookes law. Now for a linear elongation within a reasonable accuracy level, the basic equation for elongation applies. If you want to go to a higher level of detail then you can spend all day calcualting to the nth degree and get maybe a few percent more accuracy, but just spend 30 seconds, do a quick calc and the rope is sized. Job done.

 

[Denial]

As TCPhoenix says in posing his question, the effective axial stiffness of a wire rope depends on a heap of things. It is best to get the value from the manufacturer. This is what CanuckMiner has done with the effective E values he cites, values which reflect twist effects, void ratios, strand interplay, etc.

Then, before putting the wire rope to work, apply a proof load to it so that what CanuckMiner refers to as the "constructional or permanent stretch" is taken out to as great an extent as possible.

The formula might be simple and basic, 40818, but not the values you feed into that formula.