On Wednesday, August 13, 1997 at 12:30:00 PM UTC+5:30, Gearhart, Lee (corp) US wrote:
> Seth Eliot wrote:
>
> >What are "S, B, or A" in non-military metallurgical terms?
>
>
> To elaborate on Christopher Wright's answer:
> An S basis value is taken from a specification. For example, if I buy hot
> finished, annealed, 304 stainless steel bars using ASTM A276 as my purchasing
> specification, the bars have a yield strength of 30 ksi and a tensile
> strength of 75 ksi. If I test them and they show lower values, I can reject
> the material. So my S basis yield strength is 30 ksi, and tensile strength
> is 75 ksi.
>
> Yet I do not want to use these values if I am designing something for which
> failure would be catastrophic: a jet engine, for example. Strength values
> that are based on a statistical analysis of many tests are preferred for
> critical designs, and this is where A and B values are used.
>
> A basis means 95% confidence of 99% exceedance, which is best explained as
> IF a test program of 100 tests were run, and
> IF this test program were repeated 100 times,
> THEN at most 1 out of 100 test results will be below the A basis value in at
> least 95 of the 100 test programs.
>
> The B basis values mean 95% confidence of 90% exceedence, and is similar.
> Section 9 of Military Handbook 5, Metallic Materials and Elements for
> Aerospace Vehicle Structures contains the statistical formulas for
> determining basis.
>
> Sorry to drone on, but I ve had a number of discussions , usually with new
> design engineers, on why they can t use the typical strength value found in a
> manufacturers brochure.
>
> Lee Gearhart lgearhart.inc@moog.com

Thanks Gearhart for enlighting us. Can you suggest very basic reading material about A-basis, B-basis or S-basis ?? Which will be more normally.
Vikas
(India)