1. ## Cable stresses

Hello guys,

i am new to this forum and currently a student of mechanical engineering. I have a problem in mind that I cant figure out. If I have a cable made of various materials (copper,rubber,etc.) how can I calculate the maximum load that it can withstand? If I was dealing with copper only, I would find out the stresses that the load is causing and then relate them to yielding stress. However, how do I go about this problem if I have multiple materials with different yielding stresses? Do I look at each materials stresses individually and they all have to be smaller then their respective yielding stresses? For the record, I am talking about a cable with rigid support simply hanging from the ceiling. Any help will be appreciated. Thank you!

2. Are these different materials configured as concentric cylinders (copper inside rubber inside plastic etc) or as separate lengths connected to each other like a chain (a length of copper connected to a length of rubber connected to a length of plastic etc)? The calculations for each would be different.

Assuming the concentric configuration, you should also remember that these materials will have different moduli of elasticity. Individually they will stretch different amounts for a given applied load (strain vs stress). But as an assembly of multiple bodies they are all constrained to stretch by the same amount. One of the members will contribute the greatest amount to the load carrying capacity of the cable assembly, probably the copper. I would assume that member carries ALL the load, calculate its resulting strain, and then check to see if the other members can withstand that same amount of strain without failing.

3. Originally Posted by jboggs
Are these different materials configured as concentric cylinders (copper inside rubber inside plastic etc) or as separate lengths connected to each other like a chain (a length of copper connected to a length of rubber connected to a length of plastic etc)? The calculations for each would be different.

Assuming the concentric configuration, you should also remember that these materials will have different moduli of elasticity. Individually they will stretch different amounts for a given applied load (strain vs stress). But as an assembly of multiple bodies they are all constrained to stretch by the same amount. One of the members will contribute the greatest amount to the load carrying capacity of the cable assembly, probably the copper. I would assume that member carries ALL the load, calculate its resulting strain, and then check to see if the other members can withstand that same amount of strain without failing.