2001 P Kentucky State Quarter Mint Error - Cud

I can offer an explanation based on my engineering experiences:

If you consider the die surfaces and devices from a metallurgical standpoint there is absolutely a wide distribution of stresses imparted on the die during the coin striking process.

The largest magnitude stress occurs where the devices make sharp turns such as a 90 degree angle - these locations are known as 'stress concentrations'.

It is these stress concentration locations where the strain (think local elongation) on the underlying metal is the greatest and eventually the repeated stress/strain at that location causes the metal to fracture.

All metals have a fatigue life - and when the repeat stress and resulting strain cycles add up eventual small cracks then ultimately fractures will occur.

Think about opening a steel paperclip and bending it back and forth numerous times about one point - that is essentially what is happening at the stress concentration points in a die.

If those stress concentration points happen to be near the rim, with corresponding stress cycling, then Cuds will appear over time in apparently the 'same' location because, well, all of the die devices for a particular design are the same.

I have no doubt that metallurgists at the US Mint try their best to 'encourage' die designs that minimize stress concentration points - but if they had freedom over die design we would end up with quite bland coinage free of sharp corners in the devices.

So - cheer for your Cuds - they are an example of metallurgy responding to elegant die features.

Edit to add - the same metallurgical reasoning applies to why we find die cracks in similar locations across a series of coins. A classic example are the die cracks that begin at the lower corner of the Lincoln Memorial on the reverse of a LMC. That sharp corner of the building is a strong stress concentration point - and those cracks are the result of metal fatigue leading to local failure from repeated stress and strain cycling.

Hope all that makes sense!

Wow. Thank you so much for that thoughtful and detailed explanation as I really learned a lot from reading it. It is always a great day when I can wake up and learn something interesting from a professional, and today is such a day. Again, thank you for taking the time to really put me on the road to actually understanding why these things happen as they do.

Nice Cud TB, Great explanation Nickel