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Elastic modulus of wire rope

Elastic modulus of wire rope

This question is automotive-related only because I'm working on a trailer that will haul a race car.

I don't have an M.E. degree and I couldn't find the answer in Machinery's Handbook.

I need a ballpark value of modulus of elasticity (in tension, of course!) of a cable of 1/2" diameter, 6 x 19, galvanized finish. Assume the material is a "good" steel alloy with a nominal modulus of 30 x 10^6 PSI.


RE: Elastic modulus of wire rope

You might want to repost this on one of the civil engineering forums.

RE: Elastic modulus of wire rope

It will depend a lot on the lay up and twist.

I presume the 6 19 is number of yarns and number of strands per yarn.

I can't answer your question, but I would think whoever does, needs the twist data.

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RE: Elastic modulus of wire rope

You need to contact the mfgr of the wire rope, and ask for typical data.  The data will not be very reproducible from batch to batch of rope.  The stretch-vs.-tension curve will also not be repeatable unless you first stretch to a maximum expected load, then unload and repeat (due to movement of the individual wires as the rope is loaded, there is a lot of hysteresis in the rope stretch curves).  If the wire is wound onto a winch drum it will similarly change its stretch vs. tension curve further (but by much smaller amounts if the winch drum was properly sized) with each wind/unwind cycle.

RE: Elastic modulus of wire rope

Kind of begs the question of where in the middle of "hauling a race car" is this rope being applied, since most hauling applications use trailer hitches to make the connection.  

There ought not be any self-created structure that's being loaded under use.  That's just asking for lawsuits if it ever breaks.


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RE: Elastic modulus of wire rope

For example:

My book shows:

3/8' 6 x 19 FC IPS has a breaking strength of 12,200 lbs and a safe load of about 1952 lbs. using a 5:1 Safety factor.  Don't ask why it is not 12,200/5 = 2440 lbs. cause I don't know!


RE: Elastic modulus of wire rope

the smaller cable on my come-along sinks into the cable wound on the drum before doing anything useful

RE: Elastic modulus of wire rope

It might be on a winch designed to haul a car onto the trailer, even if the car is broken. It might operate a tail gate or ramps or tilt mechanism or dual level mechanism.

BT and Greg gave the best advice in my opinion.

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RE: Elastic modulus of wire rope

All answers very helpful- Thanks!

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