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niall.smyth
Posts: 18
Registered: ‎02-20-2012

Stress test using a nylon rope

237 Views, 2 Replies
06-14-2012 11:01 PM

I am carrying out a simulation to find out the axial forces in a nylon rope when a load is applied.

 

I am using non linear MES with truss elements (sub-divided) to define the rope and the analysis with large deformation switched on.

 

I need to find out the force which results in the rope when the weight is applied.  One load case is when the rope is vertical and held by a pin constraint at the top, the other is when the load is applied to the midpoint of the rope with two pinned constraints at either end.

 

My question is how do I relate the Youngs modulus of the rope to specify the dashpot coefficient for the element and how does the dashpot coefficient affect the stiffness of the rope?

 

Also how do I specify the damping in the material definition when specifying curved elements?

 

Many thanks in advance and any help is greatly appreciated.

 

Niall

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INACTIVE_AstroJohn
Posts: 492
Registered: ‎03-25-2010

Re: Stress test using a nylon rope

06-15-2012 07:09 AM in reply to: niall.smyth

Hi Niall,

 

This sounds like a homework assignment, so I hope these answers are not directly related to the grading. :smileyhappy:

 

There is no correlation between the Youngs modulus and any type of damping, whether it is the dashpot coefficient or the material damping. Unless some other information was given from which the damping can be determined, you can leave the values at 0.

 

Regardless of what values you choose for damping (0 or anything else), damping does not affect the force in the rope once it reaches its static equilibrium. Once the motion stops, there is no damping. (damping * velocity = force = 0 when velocity = 0)

 

Sincerely,
John Holtz, P.E.
Senior User Experience Designer, Simulation
Autodesk, Inc.

Current version of Mechanical & Multiphysics: 2013 SP1 (2013.01.00.0012 28-Jun-2012)
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Contributor
niall.smyth
Posts: 18
Registered: ‎02-20-2012

Re: Stress test using a nylon rope

06-15-2012 02:23 PM in reply to: INACTIVE_AstroJohn
Hi John, Many thanks for your response, looking back my question does seem like a homework assignment! Unfortunately not, my goal is to simulate a drop test to test the integrity of a lanyard for fall restraint from various heights so I would have to incorporate impact loading. Your response is very helpful, would I be correct then in saying that I have two options- Option (1) Carry out a static load test using non linear truss elements and input a force that incorporates impact loading worked out from the height fell and the max static deflection. or Option (2) Carry out a Mechanical Event Simulation in which I would have to know the damping properties in order to see how much force is transmitted through the rope due to impact/rope elasticy i.e. draw a spline to simulate the rope (subdivided) in the pre impact position and then apply a force and see how the rope arrests the fall? cheers, Niall
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