Brittle Lacquer Technique of Stress Analysis.

[Henry W]

I thought the info posted from sailawayrb and mobile_bob in another topic was too important to get lost so I posted their quotes here.

And yes, I love red paint!  This paint is special in that it will flake off if there are any stress concentrations in the cast iron.  So it provides some advanced warning of potential component stress failure.

[Henry W]

iirc the paint thing goes back to the "brittle lacquer" used to do what Rob alludes to
the idea being nitrocellulose lacquer is very hard when cured, and will crack before a casting or other part painted with it
would fail.

it was used a lot before puter simulation and stress analysis (finite analysis?) became mature and common, and it was referred to as the "brittle lacquer" test.

this is something i was trained to look for as a mechanic, and certainly applied in millwright work with component saws and flip  jigs,  you see a crack in the paint, you best stop and look hard at why it is cracking, because it doesn't crack unless something is flexing, twisting or distorting.

of course some things are allowed to flex, twist or otherwise distort,... springs come to mind, but other things
such as a motor hub holding a 30 diameter circular blade with carbide teeth turning 1740rpm you don't wanna see any distortion, or cracked paint.

every time i replaced a hub or anything that if it were to crack or break  could cause serious damage, or threat to the operator, i painted it with red lacquer, a nice coat of good coverage.  everyone thought  it was because i wanted it to look nice or not rust. ... nope!

[Henry W]

UNCLASSIFIED BY:

US ARMY ABERDEEN PROVING GROUND (STEAP-MT-M)
ABERDEEN PROVING GROUND, MARYLAND 21005

US ARMY TEST AND EVALUATION COMMAND
TEST OPERATIONS PROCEDURE

BRITTLE LACQUER TECHNIQUE OF STRESS ANALYSIS

Approved for public release on August 5th, 1981, distribution unlimited.

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