Steel/Aluminum failure benchmarks? 1

[PaperClipFixesAll]

Does anyone know of a site that either has videos or photos with practical failure tests of various steel and aluminum structural members? By practical I mean, say, a 5 foot long piece of 2" steel square tubing suspended between two columns and then have weight added until it buckles?

The reason I ask is because my current machine design job has me working with large machinery that weighs several thousand pounds, but since my practical experience with failure is limited to light materials like plastic,etc. I tend to overbuild and over-design things because I can't really visualize how much stress the material can take without running the FEA and I always assume it's much weaker than it really is.

 

[metman]

This sounds like too simple to require FEA. It sounds like a simply supported beam of square tubing.

If you do not have access to a strength of materials textbook then a machinery's handbook will have all the info you need. It will give you the diagrams to choose from that depict your loading condition and the corresponding formulae for stress and the section modulus or moment of inertia for the tube in another table and the yield strengths for the various steel or aluminum alloys in other tables.

If you do not understand these basics of design, attempting to overdesign when you know not whether you are actually overdesigning is a dangerouos approach at best.

I do not mean to criticise rather being cautionary.

 

[Guest102023]

Ditto, FEA sounds like overkill for this job.

With machinery, you don't want to design just strong enough to avoid failure from dead weight, it requires a certain amount of rigidity, as well as resitance to vibration. A simple square tube may well be strong enough to simply support the dead weight with a healthy safety factor, but may be insufficient in other respects. It looks as if for this bracket(?), a few judiciously selected elements joined by welding should do the job.

Any local fab shop big enough to have its own designer should be able to create something for you.

 

[PaperClipFixesAll]

no, I think you both are misunderstanding what I'm talking about.

First of all, I'm not designing anything remotely that simple. I've already designed a handful of oilfield drilling and abandonment tools working in my intern/jr. engineer position under a PE. While my core designs were great and required little or no modification to the geometry or mechanics, I have a tendency (for example) to use a 2" thick plate where my boss corrects me to just use a 1" plate (our tools are mostly one off and are thus made predominantly of flame cut plate steel) . In other words, I always underestimate the capabilities of the material and in sophisticated machine design it's hard to get a good estimate of factor of safety even with a good FEA program.

Therefore, I want to just see some video of just some basic pull tests, torsion tests, etc. of basic members and forms of steel with the forces noted so I can get an idea of what kind of stresses steel can take in different basic configurations so that when I'm designing I have a better idea of what to expect when the whole thing comes together.

Believe me, by no means did I ever mean to insist a factor of safety of 1 is acceptable nor was sophisticated FEA necessary for a square piece of tubing between two columns. I know I could probably just run these different tests in Solidworks, but I'd rather see a real piece of metal undergo the deformation.

To use an analogy, I want to be the machine design equivalent of a chef that never has to measure his ingredients because he always knows just the right amount to use. Not to say I would be reckless and not run FEA and have it pull tested, etc. but just to be able to design it almost perfect the first time instead of having to "guess and check" multiple times and have to keep modifying several parts to get the geometry back when I change plate thicknesses or pin hole sizes, etc. etc.

Do you understand now?

 

[metman]

PaperClip,
Maybe now I am starting to get a clue. Strength of material derivations for determining values of strain are based upon very small deflections whereas deflections required to reach yield strength or ultimate tensile strength are dramatically larger values.

However, as you say there are tensile tests. These tests give us values of Yield and Ultimate and as mentioned before these values are readily available.

...so I can get an idea of what kind of stresses steel can take in different basic configurations...

These tensile tests provide the values for the "kind of stresses steel can take." The stress can be calculated for these basic configurations. Therefore I am missing some parts of you point.

OK -- when you see and hear a .505" (12.8mm)diameter steel tensile specimen separate, it is impressive. It sounds like a small cannon and even though the frame of the tester is stout or rigid as brimstoner would say, there is a lot of jumping around of stuff before the dust settles. This of course helps to get a personal feel for what steel members can withstand.

This background has probably helped me in my design experience for an initial trial during the preliminary layout of a design but I still do not feel comfortable designing by the sea of my pants and always go through the numbers to whatever extent possible and sometimes find that I am off -- like you -- by a factor of two times or maybe even more.

Is there a mechanical test lab anywhere near you? Maybe they will allow you to come witness some pull tests or bend tests.

 

[Compositepro]

What you are asking for is to get real world, relevant experience quickly and on-demand. It is not realistic. Every experience is a learning experience. Every time you see a construction site you have an opportunity to look at cranes and heavy equipment in operation. The main determinant of how much you learn from experience is a quality called curiosity. You can also find what you want on You-Tube. But you will learn little from watching videos if you don't devote the concentration and attention to detail required to learn something. From your question I suspect that your real problem is a lack of inherent curiosity.

I really enjoy watching shows like "How It's Made" even though the narration is awful and often wrong. You can learn a lot if you are interested and curious. Most people are not.

 

[PaperClipFixesAll]

While I think you are closest to understanding what I'm looking for, compositepro, you actually have it backwards from my intent. If I wasn't curious and looking to better my inherent "feel" for materials, I would never have even made a post to begin with. I want the engineering equivalent of what a medical student gets by watching videos of surgeons at work. It's not the same as experiencing it first hand, but it's alot better than nothing at all. Simple material pull tests don't really help anything because materials are almost never loaded in pure tension. I don't see how videos like "How it's Made" would help anything in this matter because that's more about manufacturing processes than designing to withstand large stresses and rarely delves into any real engineering concepts. And, for the record, I already downloaded the complete series of How it's Made from bittorrent some time ago.

If you have seen anything on youtube like what I'm talking about, some examples would be nice, or at least some key search terms.

To further clarify, I'm looking for something like this but with more simplified structures and more off-the-shelf materials:

http://www.youtube.com/watch?v=CqK83ySMH_s

NOT this:

http://www.youtube.com/watch?v=YdqvGGFIbfc

No matter what you claim, there is no better way to learn about materials from a strength standpoint than to see examples of failure and knowing the weight and conditions involved. I've seen a few pull tests of equipment myself, but if it's not brought past the yielding point, it hasn't really told me anything other than it's overbuilt (which it should be, but too overbuilt wastes money and can make it unwieldy due to weight).