# OT: Tensile strength of steel

Discussion in 'Electronic Design' started by linnix, Aug 29, 2008.

1. ### linnixGuest

This is not really electronics, but most of us are engineers here.
Right?

I need to estimate the tensile strength of a steel bar of 25mm width
and 1mm thick.

Do I have the numbers correct?

Using low end estimate of 400MPa steel.

400 MPa = 400,000,000 Newton / sq. meter

25mm x 1mm = 0.025 * 0.001 = 0.000025 sq. meter

400,000,000 * 0.000025
= 10,000 Newtons or 2250 pounds (4.4 pounds per Newton?)

2. ### JeffMGuest

The book I consulted says there's a grade even lower than that:
The math looks kosher to me.

3. ### linnixGuest

It's stainless steel screwed on a piece of wood to increase the
tensile strength of the structure. It could be subject to a few
hundred pounds of vibrations, but no where near 2000 pounds. I just
need to figure out if it should be 1mm or 2mm thick.

4. ### Dirk Bruere at NeoPaxGuest

Any failure is likely around the screws

--
Dirk

http://www.transcendence.me.uk/ - Transcendence UK
http://www.theconsensus.org/ - A UK political party
http://www.onetribe.me.uk/wordpress/?cat=5 - Our podcasts on weird stuff

5. ### neon

1,325
0
Oct 21, 2006
I guess he means stainless steel as opposed to cold roll stell. WELL ANYHOW POUNDS/1000 feet /circular mil is 0.002671 now you do your conversation you may get a A. NOW THAT IS AT 20 DEGREES

6. ### Rich GriseGuest

How do you intend to fasten it? In any case, if it's attached to wood,
then the part that fails won't be the steel.

Good Luck!
Rich

7. ### JosephKKGuest

Typical SS runs about 35000 PSI at yield (3% elongation). Useful
capacity is not over 15% of that. Your dimensions are about 0.038
square inches for 1 mm thickness. 35000 * 0.15 * 0.038 = 199.5 lbf. I
recommend at least 2 mm.

8. ### linnixGuest

I would expect yield strength of 50%, not 15%. But as someone already
mentioned, wood tissue around the screws could be a problem anyway.

9. ### linnixGuest

Sorry, we are both wrong. I read your message wrong. SS is 70PSI
tensile and 35PSI yield. You got my size wrong. It should be 35000 *
0.15 * 1 (25mm is approx. 1") = 2000 pounds.

10. ### Tim WilliamsGuest

I should hope not; you meant KSI right?

(Hmm, are there even any materials with single-digits PSI yield? Jello
perhaps?)

Tim

11. ### linnixGuest

Yes, you are right. It's KSI.

12. ### Tim ShoppaGuest

Maybe it's just english, but I'd describe a 25mm x 1mm shape not as a
bar but as a 1-inch wide strip of 20-gauge sheet metal.

Now you're drilling or punching holes in that sheet metal, and then
you're going to subject it to vibrations of hundreds of pounds.

Maybe what you describe (wood, sheet metal strips, etc.) are more
appropriately described as "banding", like what they put outside a
wooden crate for a little extra strength?

1: Whatever fastener system (screws? glue?) you're planning on using
will probably fail long before the metal does.

2: Hundreds of pounds of vibrations are not things to ignore. With
many metals, if you know the rig is going to be seeing hundreds of
pounds of vibrations, you have to design for a static strength in the
thousands of pounds.

3. Sheet metal... bent around corners? I can guarantee that when it
does fail it'll fail at a sharp corner!

Tim.

13. ### JosephKKGuest

Umm, 1 mm is a little less than 0.040 inch. 25 mm is about 2 % less
than one inch, i stand by my very conservative cross section estimate.
It is highly desirable to stay well below yield. (say 15% of yield.)
Ultimate tensile strength is at the breaking point, not a real
operating load. At least that is the way i read the "Metals
Handbook, (1963) Volume VI properties and material selection", IIRC.
Took the book to work to clarify some discussions about various
materials and typical strengths.

14. ### Tim ShoppaGuest

Nothing wrong with going to the books to look up material
properties, but it's amazing that anyone here thinks that
this is the only concern when someone wants to support
something that vibrates with hundreds of pounds of force
with a piece of sheet metal an inch wide and as skinny as
20 gauge all held to a wood support with a screw.

In other words, it's not just material handbooks and multiplication,
there's some handyman's common sense that ought to come in too .

Tim.

15. ### linnixGuest

I find it hard to believe that the usable range is so low. Yield is
where it deform permanently, but temporary deformation is OK (for
example: a spring).
Actually, it's more like 18 guage (1.27mm) with six screws of various
length and sizes (long thin one and short thick one). There are also
plywood on top and other supports around. Worst case is a 200 to 300
pounds person jumping directly on top of it, which would create
tensile forces parallel to the plate, but perpendicular to the
screws. But I am still open to 10 to 12 gauge metal plates.

16. ### Tim ShoppaGuest

You're now talking about human safety! It sounds worse every time you
talk about it, you should not support a human with a one-inch wide
piece
of skinny sheet metal attached to wood with a bunch of screws.

For non-human loads, it is common to derate ropes and chains (under
tensile load) by a factor of ten to fifty from their breaking load.
The derating factor
for a strip of sheet metal and a non-human-safety load has gotta be
far far more severe. And I don't personally get to deal with anything
involving
human safety.

And finally, a 300 pound guy jumping a foot and coming back down,
stopping in a fraction of a second, is a force far far greater than
300
pounds.

You should probably be asking someone familiar with OSHA safety
requirements etc. for railings and platforms and fire code
requirements
for fire escapes. There is far far more to engineering a safe
structure
than looking up some numbers related to a material in a handbook!

Tim.

17. ### linnixGuest

OK, I'll go with 2mm steel bar. The structure is mostly jointed with
1mm steel plates. I am just trying to reenforce the weak points. The
25mm x 2mm steel bar should give me at least 5000 pounds yield
strength.

18. ### linnixGuest

Douglas Fir, or similar construction wood has a tensile
strength of 87MPa (12.6KSI) in the X direction (lenght) but only
2MPa (290PSI) in the Y direction (width) Stainless steel has
a tensile strength of 860MPa (125KSI) in either direction.

For a typical 2x4 wood (cross sectional area of 8 sq. in)
and stainless steel plate of 4x0.04 (18 guage steel plate),
Wood has a cross sectional area of 12 times of steel.

So, steel has 80 percent of tensile strength of wood
in the X direction, but 30 times in the Y direction.

My purpose is to reenforce the weak Y direction tensile strength.
Shouldn't 1mm steel plate be more than enough? What am I missing?

19. ### Rich GriseGuest

Use Southern Yellow Pine. To see how a support structure is made,
find a wood roller coaster, buy the attendant a 6-pack (or bottle),
and have him show you the details.

Good Luck!
Rich

20. ### JosephKKGuest

Three things:

1.) No sane engineer designs anything at more than 10 % of failing
strength. That is the meaning of the upper number of tensile
strength, that is when it breaks over 95% of the time. There are also
differences between fairly elastic materials like most metals and
fairly inelastic materials like wood, and brittle materials like most
ceramics.

2.) Stated dimensions are not always the physical dimensions. For
example a finished 2 by 4 is actually about 1-3/4 by 3-1/2 inches; go
ahead put a measuring stick to it.

3.) I will not even touch this any more without dimensioned drawings
with fully declared materials. I have many civil engineering friends
that will help just for the asking, but they will not do it
blindfolded and hogtied by inadequate information.