Re: OT: Tensile strength of steel
- From: JosephKK <quiettechblue@xxxxxxxxx>
- Date: Thu, 04 Sep 2008 23:23:12 -0700
On Wed, 3 Sep 2008 21:34:12 -0700 (PDT), linnix
<me@xxxxxxxxxxxxxxxxxx> wrote:
On Sep 2, 9:13 pm, JosephKK <quiettechb...@xxxxxxxxx> wrote:
On Mon, 1 Sep 2008 13:41:32 -0700 (PDT), linnix
<m...@xxxxxxxxxxxxxxxxxx> wrote:
On Sep 1, 1:06 pm, linnix <m...@xxxxxxxxxxxxxxxxxx> wrote:
On Sep 1, 11:29 am, JosephKK <quiettechb...@xxxxxxxxx> wrote:
On Thu, 28 Aug 2008 23:28:00 -0700 (PDT), linnix
<m...@xxxxxxxxxxxxxxxxxx> wrote:
On Aug 28, 10:48 pm, Tim Wescott <t...@xxxxxxxxxxxxxxxxxxxx> wrote:
On Thu, 28 Aug 2008 19:05:04 -0700, linnix wrote:
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?)
The math looks right. Steel only gets to it's ultimate strength in a
laboratory -- in real life it always fatigues, or buckles, or does some
other real thing that the math doesn't cover well.
Figure that if it's going to rust or be subject to repeated stress that
you need to derate that calculation by at least a factor of 10 -- and
don't take my word for it, I'm just a gearhead, not a mechanical engineer.
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.
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.
I would expect yield strength of 50%, not 15%. But as someone already
mentioned, wood tissue around the screws could be a problem anyway.
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.
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.- Hide quoted text -
- Show quoted text -
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?
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.
.
- References:
- Re: OT: Tensile strength of steel
- From: linnix
- Re: OT: Tensile strength of steel
- Prev by Date: Re: Arctic sea ice
- Next by Date: Re: Arctic sea ice
- Previous by thread: Re: OT: Tensile strength of steel
- Next by thread: Re: Long life lights
- Index(es):
Relevant Pages
|
