Dip Net: shape vs strength

You did not provide the wall thickness of the tubing, but it seems likely that both strength and stiffness of the 3/4" aluminum tubing will be substantially greater than that of a 3/8" steel bar for any reasonable selection of wall thickness.

I'm not sure I understand what you mean by which shape would be stronger but the rectangular shape would produce less moment on the end of the handle because the center of force is closer to the end of the handle.

I think the aluminum would be lighter and would not rust or require special coating. Steel would be heavier and require treatment and would still rust.

I agree with post #1, on the 3/4 being stronger than the 3/8".

I bet on the oval net because the tubing is attached to the handles with no sections of the tubing perpendicular to the handle. That will minimize the twisting of the tubing when moving through the fluid.

OK.....

So we have a consensus that the 3/8" tubing would be stronger against bending than a 3/8" cold rolled steel.

Now how about the shape? ........... so far, 1 to 1.. rectangle : oval

Can someone translate these specs into REALLY simple terms?

Thank you.

Smitty

I'll give it a try, its pultruded plastic, not aluminum.

milo

I would ask how that affects the rod to tube question, but we would need to know wall thickness.

That being the case, I reserve my right to post a second opinion.

If the tube is not stronger, then the rod is!

What does this have to do with the problem originally posed? You were talking about an aluminum tube versus a round steel bar. Now you are talking about a pultruded polyester resin tube. This is not an elastic material and it is non-isotropic, so why are you introducing it into this thread? It is not readily assessed on a forum such as this, but, to answer your question, the specs are already in REALLY simple terms.

The specs provided are for the handle of the DIP NET that will hold the frame.

It was my oversight to not mention that .

As for already simple terms, I am NOT an engineer. The specs are not common to me and I requested a clarification from someone who is familiar. Once again, forgetting to mention that this was for the handle of the net frame.

As for NOT being readily assessed on this forum, I would almost guarantee that someone will either respond or PM me a SIMPLE explanation in terms of what these numerical values represent.

(Knowing I am NOT an engineer and asked this question because I needed an answer).

Thank you for your input.

Smitty

Smitty

Smitty,

You are comparing two shapes, an oval and a rectangle. The first shape in your diagram does not look like a true oval. If it is an ellipse, then its area is 20*14*pi/4 = 219.9 in² and its centroid lies 10" from the end of the handle. If it is loaded with a uniform load, w uniformly spread over its area, the moment on the end of the handle will be 2199w.

In the case of the rectangular shape, the area is 280 and its centroid is only 7" from the end of the handle, so with a uniform load of w, the moment would be 1960w at the end of the handle or approximately 89% of the moment from the ellipse.

Needless to say, if you rotate the ellipse 90 degrees, the story will be quite different.

Smitty,

The flexural strength is the stress at which the material fails when subjected to bending. Pultruded tubes have no well defined failure point, so 5% strain is usually taken as failure.

Flexural Modulus is the ratio of stress to strain in flexure. If a tube is bent as a beam and has a stress of 10,000 psi at the extreme fibers, the strain will be 10,000/1.8e6 or 0.00555.

Tensile strength is the failure stress when subjected to axial tension.

Tensile modulus is the ratio of stress to strain in tension. For an elastic material, tensile modulus and flexural modulus are the same, i.e. Young's Modulus...not so for polyester resin systems. If a tube is subjected to a pure tension of 10,000 psi, the strain would be 10,000/2.5e6 = .004 or 4mm per meter of length.

Compressive strength is the failure stress of a stocky section when subjected to axial compression. Slender sections have a lower compressive strength because of slenderness coefficients.

The remaining properties are not of much interest structurally.

OK....

Thank you Bruce for the information. I believe armed with these explanations we can make a better decision on how to go with this project.

We are looking at situations where the variables are going to be widely spread across the board.

This information leads me to believe that we will need to make several designs both in Oval and Rectangle. No problems. I just like to run the portions of my projects that I am NOT familiar with, through you all here at CR4 as i am not an engineer by any means....and you all ALWAYS have answers....

Thank you all again.

Smitty