what causes case hardening???

[IMERC]

There is your answer.

so what happened to the interior of the wood....
not likely "rot" but just cellular break down as in self destructed???

[WDH]

Sounds like the core honeycombed because the shell dried too fast and the core could not reciprocate.

[SwampDonkey]

Honeycombed and possible collapse with surface checks opening up exposing busted fibre.

[Den Socling]

What do we have here? The wood went into the attic green. There is no airflow over the wood. The temperature might hit 120'.

Later the wood was "stringy/fibrous". You could "break apart with fingernails".

Honeycombed wood indicates casehardening. Honeycombed wood is hard inside. I think that rot is indicated.

Suppose that 120° and no air, shell dried the wood just enough to trap the water inside. Then suppose microbial or fungus eating away at the wood. It might explain the weak fibers.

Just my guess.

[Den Socling]

BTW I have links to the Dry Kiln Operator's Manual and to Drying Hardwood Lumber in a sticky at the top, labeled kiln operation.

[SwampDonkey]

Certainly possible, I would rule out dry rot though. That usually is a result of intermittent water flow from a leaky roof or around windows and such. Even damp manure in a barn aloud to build up against the walls in a barn due to a little laziness of the shoveler. ;) :D

[jamesamd]

Almost feels like the logs were just starting to go punkey when they were then sawed and put up to dry.
Jim

[lt70guy]

curious if the attic was vented?

[IMERC]

curious if the attic was vented?

yes....

[jimF]

As has been mentioned casehardening is created in all forming of drying, in airdrying or kiln drying.  I see no mention of the species nor what the condition of the lumber was in initially.  Since casehardening is present in all forms of drying , it is not an indication of honeycomb.
The test results for honeycomb is very sensitive to how thick the prongs are cut.  The test can indicate either casehardening or reverse cashardening coming from the same piece of lumber depending on how the prongs were cut.
Without samples or clear photos it is hard to determine if it is rot or not.

[Den Socling]

Casehardening is created in ALMOST all forms of drying. Vacuum drying can be the exception.  ;D

[jimF]

sorry, almost correct :-\