I would like to repeat my concerns on the proposals bandied about to use welding
wire or other austenitic stainless steel wire in the place of aviation quality
hinge pin.
Aircraft steels is my business and I recently sold some hinge pin wire so I
pulled the test reports from the file this week. The tensile strength was 1900
N/mm2 (277000 psi) This is because it is cold drawn to increase the tensile
properties. Similar values are achieved with piano wire.
As someone has already confirmed the usual strength of stainless wire, including
welding wire, is about 400 N/mm2 (60000 psi). It can be as much as 700N/mm2 but
the yield strength (when it starts to permenently stretch) is only about 250
N/mm2 - 36500 psi). This is because it it softened after drawing to enable it to
be cut and formed.
If you work all this back to the breaking load for the cross section of a 2,13
mm hinge pin and a 1,6 mm stainless wire you come up with some worrying figures.
2,13 mm wire = x-section 3,56 mm2 (pi X r)
1,60 mm wire = x-section 2,01 mm2 - 56% of the original X-section
Hinge wire strength = 1900 N/mm
stainless wire = max 700 N/mm - 36% of the strength
The bottom line of all of thise reductions is that a normal stailess steel wire
of 1,6 mm diameter will break with a load on it of about 80 Kg.
A hinge pin will break with a load of about 650 Kg.
Of more importance in our case than the breaking load or yield strength is the
fatigue limit. This is the level of load that above which you need to start
counting the number of cycles because soon it will fail. This is also a function
of the tensile strength and is respectvely higher for hinge pin wire.
1,6 mm hinge wire is available with no min quantity but it must be down coiled,
straightened and cut and this involves a minimum charge of pds 90 from the
manufacturer.
If anyone has any more questions please mail me.
Best regards
Barry Tennant
D-EHBT
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