Good find CBR

To me the splinter action sounds like the spalling effect. The spall knocked lose from the inside when a round does not penetrate a solid surface but strikes it with sufficient force.

The first six American Frigates were not only made from a couple of kinds of Super Oak not available to European ship builders, the wood was also treated in a special solution to impart more toughness and elasticity.

Rather than make the tables I will allow you to look up the mechanical properties of the woods.
Quercus bicolor (swamp white oak)
Quercus virginiana (live oak)

Quercus Robur (European Oak)

I know about the solution only because the last of it and the treated wood was found at Puget Sound Naval Shipyard, in a tank in the still undisclosed solution, under a building, stored there god knows how long. (It was founded in the 1850s) The wood was very much needed for the overhaul of the Constitution and that is where it went.
(from what I got the stuff is still classified)

The US tests were in all likelihood tested against Quercus alba (American white oak)
The penetration in Quercus Robur would be greater I would imagine.