Forces on a rope when catching a free falling weight

[erobz]

Answer from manufacturer:
The tensile force is measured by pulling at a speed of 300 mm per minute at intervals of 250 mm and measuring the force at rupture. We are sorry, but we do not disclose detailed data to consumers.

Thats weird. I don't know what to tell you other than you might be stuck experimenting yourself to estimate $k$.

 

[Zeusex]

Thats weird. I don't know what to tell you other than you might be stuck experimenting yourself to estimate $k$.

Yes they weren't cooperating. I will update as soon as I get results from my experiments.
Thanks.

 

[erobz]

Yes they weren't cooperating. I will update as soon as I get results from my experiments.
Thanks.

Do you have an experimental setup in mind, and do you know the material?

 

[Zeusex]

Do you have an experimental setup in mind, and do you know the material?

Yes, linear stage, linear encoder and a load cell

 

[erobz]

Yes, linear stage, linear encoder and a load cell

If it's a plastic material just be mindful of "Creep". If you put some load on it and it keeps slowly elongating over time at that load the material is experiencing "Creep". From memory I think plastics are prone to it.

 

[Zeusex]

If it's a plastic material just be mindful of "Creep". If you put some load on it and it keeps slowly elongating over time at that load the material is experiencing "Creep". From memory I think plastics are prone to it.

I am planning to first measure the length L0 when load cells shows 0 N. Then start moving the linear strange until the thread breaks. Let's say the thread breaks at 1 KN. I can then plot F vs L and would know strain: (L-L0)/L0 for the linear regime.
E - young's modulus I know from manufacturer 50 GPa.
k = AE/L0, where A is the crossectional area of thread

 

[erobz]

I am planning to first measure the length L0 when load cells shows 0 N. Then start moving the linear strange until the thread breaks. Let's say the thread breaks at 1 KN. I can then plot F vs L and would know strain: (L-L0)/L0 for the linear regime.
E - young's modulus I know from manufacturer 50 GPa.
k = E*A/L, where A is the crossectional area of thread

That can be used as a check, but you are measuring Force (with a load cell) and Length (with the linear encoder). The slope of that graph is the spring rate $k$ in the Hookean regime. Don't over complicate it with stress-strain. Put some length of rope under some small initial load. Measure the length of the rope. Then increase the load making successive length measurements at each load. Make a plot of Force vs length.

 

[Zeusex]

That can be used as a check, but you are measuring Force (with a load cell) and Length (with the linear encoder). The slope of that graph is the spring rate $k$ in the Hookean regime. Don't over complicate it. Put some length of rope under some small initial load. Measure the length of the rope. Then increase the load making successive length measurements at each load. Make a plot of Force vs length.

Sure. I will do that and share the plot. Thanks.

 

[erobz]

Sure. I will do that and share the plot. Thanks.

Most importantly. If you are determined to test to failure (I think it is unnecessary because it's beyond the scope of the Hookean model we are proposing) it should go without saying, but do this safely with PPE, and shield between you and the rope.

Probably best to keep the rope reasonably short as well. You don't want to max out the encoder stretching it.

 

[Zeusex]

Most importantly. If you are determined to test to failure (I think it is unnecessary because it's beyond the scope of the Hookean model we are proposing) it should go without saying, but do this safely with PPE, and shield between you and the rope.

Probably best to keep the rope reasonably short as well. You don't want to max out the encoder stretching it.

Sure, I will do that :)