Stronger or weaker, that is the ??

[Thomas Dean]

Had a friend ask me if twisting your material makes it stronger or weaker. I am not sure if it does or not. Could some of you gurus please explain.

[Don A]

I'm assuming you are refering to a decorative twist... "just for looks".

I have seen stress cracks in twisted sections when done under less-than-perfect circumstances; abused or over-worked steel, flawed stock, etc. I can't help to believe that even under ideal conditions, a twist would lessen the integrity of the stock, even if it's just a little bit.

This would be a good test project for folks that like to make stuff and the destroy it. :cool:

[habu68]

In my public demos I ask the visitors "why it is important for a blacksmith to always put a twist in an object? I let them guess while i take the heat. Then tell them the answer " You can get a $1.00 for it!" another thing, a twist doesn not shorten the piece.

[Tyler Murch]

Twisting pattern welded material can make it stronger. This is what the celts did during the migration era. It would pop off any scale, making better welds, and the forces of twisting after being welded would make any weak welds apparent.

[J W Bennett]

Don A,
"This would be a good test project for folks that like to make stuff and the destroy it. :cool:"



I usually destroy it While I'm making it:p

JWB

[ThomasPowers]

I should ask over at the Mat Sci dept if a student needed a project and do the test *right*.

In early pattern welding having the material twisted meant that any slag inclusion or crack did not leave a weak spot straight down the blade.

Tyler have you read "The Celtic Sword" by Radomir Pleiner? Lots of great metallographich analysis of extant blades from that time period showing exactly what the smiths did do. Try to ILL it from the public library.

[henerythe8th]

Depends on what you're doing, more than likely...
If you are twisting a piece of hot rolled square bar then you are likely "weakening" it.
Why?
It's about stress/strain and the cross-sectional properties of the piece, not to mention straightness. All things being equal, if you take a piece of "perfectly straight" rod and apply a compressive, or shortening load to it, it will be "stronger" than one that is a bit bent. Keep in mind, however, that if you apply enough force to it, that straight bar will "cripple" catastrophically. If you applied the same load to a similar bar with a bit of a bend, chances are it's going to start to move with less force, but you'll likely notice it before it gets to those levels.

Realistically, most of what we make is not loaded anywhere near what it can take (excluding knives, 'hawks and such), impact loads can create a huge amount of stress...

From a bending perspective, still considering the HR square bar, the quench that the steel is put through will likely modify the properties of the material more than the twist will modify the the properties of the cross-section...

...this could become a huge discussion, with many different opinions...

Let's see where it goes!

Henry

PS--Bachelors degree in Mechanical Engineering...

[Tyler Murch]

Thanks Thomas. Sounds cool. I'll look that up.

[irnsrgn]

Back to the original Question. Is a twisted section stronger than a straight section. I am assuming this is in reference to a decorative twist in a square solid structural member.

1. Rolled iron has a grain to it due to the rolling process and in theory it will take more effort to bend it one way due to the grain structure very similar to the way the grain effects a piece of lumber.

2. Square is like Flat in that it easier to bend in the direction of a flat side than it is to bend in direction of one of its corners. This is because there is more metal to stretch and or compress in this direction.

3. It stands to reason that a twisted square section is stronger than a non twisted section as the corners or high spots are all the way around the section, not just at the corners.


When I made the grill guard - Deer deflector for my suburban I used 1.5 inch by 3/16 wall square tubing and placed it on an angle with the corners up and down and front to back to gain addition strength from a small light material. This had the added advantage of more or less parting the wind stream in a more efficient way and reducing the drag from a flat surface.

(Note), this guard has successfully deflected 7 Deer to date with no damage to the front of my vehicle. One of them at 55 mph. In this instance the deer appeared from nowhere at night and the thump of its suicide mission was a complete surprise. It flew at least 20 feet to the right front just enough that I didn't run over it. Oh yes, the guard is not fastened to the bumper, its fastened to the frame of the reciever hitch I installed under the front which is securely bolted to the frame of the vehicle.

[Quenchcrack]

First, nobody said whether we are twisting hot or cold. Cold twisting will strengthen the steel due to cold working (work hardening). If done above the recrystalization temperature (about 1000-1100F), the effect will be negligible. Now for something totally different. There is something called the Bauschinger Effect. When steel is loaded to exceed the yield strength in tension, the yield strength in compression is diminished proportionally. The same is true of yielding in compression that lessens the yield strength in tension. The Bauscheinger Effect can be mitigated by stress relieving the material. This strongly suggests that cold working and the Bauschinger Effect are related to a reduction in dislocation mobility due to disorganization of the crystal lattice in the metal. Recrystalization and stress relieving allow the lattice strain to be relieved and the atomic organization re-established. This allows for a free movement of the dislocations until they are again pinned due to cold working. So until we know the temperature of the work piece and the degree and direction of strain, we cannot actually give an answer.

PS: Professional Masters Degree in Metallurgical Engineering- Whoopie!

[Thomas Dean]

THANKS folks! got some great stuff going here and I appreciate ALL of the response. Some of it goes a tad over my head but gives me great stuff to research. (Bauschinger Effect.)
Sorry about some of the confusion but the twisting is done HOT (bright red to orange), decorative (same direction or reversed twists. The pieces in question are to be table legs, starting out with 1"sq bar, forged to round with approx. 1/4" 'wings' on opposite sides down the entire length of 4ft. (=O=, looks similar to this, sorta, kinda, maybe a little ) Quenching (if any) is done only after cooling well below 900F.

[Hofi]

When Twisted Hot There Is No Change In Strength Tensile Or Bending. The Crosscut Of A Twisted Square Bar Is Always The Same Like The Original. If U Twist A Pack Of Cards U Get A Spiral Line Outside But The Card Dose Not Change.
Twisting Cold Steel Will Make It 20% Stronger For Bending And Tensile. It Is Called ''sygma'' Steel And Is Used In The Concrete Constructions To Lessen The Amount Of Steel Used