On Fri, 24 Jul 2020 19:29:46 +0100, The Natural Philosopher
wrote:

On 23/07/2020 12:47, AnthonyL wrote:
On Tue, 21 Jul 2020 13:56:57 +0100, The Natural Philosopher
wrote:

On 21/07/2020 12:49, AnthonyL wrote:
On Mon, 20 Jul 2020 17:27:28 +0100, The Natural Philosopher
wrote:



It somewhat reminds me of what I learnt as an engineer "Safety factor
is simply ignorance factor".

Sounds ******** to me. Safety factor is the margin to known problems.
Says nothing about unknown problems, but how could it?


https://en.wikipedia.org/wiki/Factor_of_safety
or more precisely the "Margin of safety"

That has nothing to do with unknown problems and has everything to do
with the uncertainty of the anticipated behaviour of the materials in
question.

Ignorance === unknown.

I didnt start the use of that term, I merely replied that 'ignorance
factor' implied 'margin for unknownn (problems)

Albeit a long time ago I also spent a lot of time calculating (before
ready access to calculators) Mean Time Before Failure and Operational
Reliability of sub-systems in an engine.

No doubt any safety factor applied nowadays would be much more refined
than in those days as the manufacturing and build processes improved
and the ignorance factor decreased.

What 'ignorance factor'?

You have categorically stated that this has nothing top do with unknown
problems, therefore there is no 'ignorance factor



The ignorance factor is the uncertainty in the reliability of the test
measurements taken against any sample, it has nothing to do with
unknown outside influences.

The tensile strength of Steel, structural ASTM A36 steel is
250MPa. Well exactly? All? Most samples? If you're life depended
on it would you apply that load and feel safe? Would design engineers
be prepared to put their reputation on that figure? Or might you
calculate everything at 230MPa just to give you a margin of safety
because you want to be sure (ie because you are not sure)?

These are not external unknown problems which is the way I had
interpreted some of the criticism of my statement. If a plane crashed
into a building that was reliant on the 250MPa structural frame that
is beyond the design criteria. If the plane crashed because a wing
failed because a bolt snapped because it had no safety margin built
into the design then that smacks of overconfidence/negligence and a
slight application of extra material would have saved the day if the
designer had understood that the full behaviour of the bolt was not
exactly understood, ie ignorance factor as cited to me many years ago.


--
AnthonyL

Why do scientists need to BELIEVE in anything?