In softball and baseball it's common knowledge that you can "break in" composite bats. They get hotter and hotter and hotter and then... Shatter. Especially the case for big hitters.
I'd bet that it's the same with a carbon face club. As the epoxy and fibers break down due to impact, they'll become more and more flexible, increasing CT/COR... Until they break!
Rule 4.1.a Clubs Allowed in Making a Stroke
(1) Conforming Clubs. In making a stroke, a player must use a club that
conforms to the requirements in the Equipment Rules:
• A club used to make a stroke must conform not only when the club is
new, but also when it has been deliberately or accidentally changed in
any way.
• But if the performance characteristics of a conforming club change
because of wear through normal use, it is still a conforming club
Should have read the small print
When a used club is pendulum tested (see Part 2 Section 4c(i)) in the
field and a result in excess of 257 μs is attained, the specific club will
be deemed to be damaged into a non-conforming state, based on the
presumption that it conformed when new and was included on the List of
Conforming Driver Heads.
For reference the limit for new driver heads is 239 μs with a 18 μs tollerance.
My main point was the ignorance of the GC talking heads talking about “metal fatigue” on a carbon faced driver when Rory’s previous driver in question was the first gen Stealth.
Yep. I think the PGA Tour has their own 'Local Rule' on this also. Devil's in the details. 
but here's a hot take on such vague wording:
is using a club that you know that, with respect to its manufactured quality is broken ( or in process of breaking)
"normal use" . It seems like to me that if I had million(s) riding on a single given shot and the club could fail with much higher probability than normal on a given shot, I would take it out of play. Hell, I'd take it out of play just because I wouldn't want to ruin a round if I had a greens fee greater than $100 riding on it. LOL.
Rory should really start keeping his mouth shut...complaining at Bay Hill...Maybe he needs to practice and focus on his game instead of blaming equipment like a 20 handicap? What people need to know, and cry baby doesn't mention ( or maybe doesn't realize) is that clubs are deemed non conforming for many reasons. And it doesn't always make the club better of worse. Things from Hotter faces to caved in faces to sitickers on the clubhead ALL make the club non conforming.
If Rory has been hitting the same driver head for a year of so, the constant pounding at that speed could make ANY clubface non conforming. Its up to the USGA to test them. For him to blame his playin that... shooter move.
Typhoon I think you've misunderstood what Rory said. The article I read had his direct statements in quotes.
He basically said that knowing his drives were getting so long, he suspected the club may no longer be conforming. The tournament he was at was testing drivers, apparently on Friday, so he changed his out Thursday night, without having it tested.
I'm sure that was a 'face saving' move, no pun intended. But this does tell the public just how often he has been called on for driver testing. Maybe never?
ode Exactly… does Rory or half the guys on your know how far any of their clubs go? I don’t think they’re a bright bunch. The caddie has to tell them every yardage, where to aim, has to tell them they are good, they got this shot, stay in the moment…
Seriously, you guys that have jobs… is there someone standing next to you all day telling you what to do and reminding you that you are good at your job?
This crap happens a lot probably, and nobody else feels the need to be in the spotlight for saying it.
IMO a lot of the confusion comes from the frase "breaking in" your breaks, a driver,... in Queens Kings English this is "betting in". This was translated by US jounalists as "betting on" a new driver. Rory explained that he had a mishit he could not explain, so he assumed his driver was about to crack, got a new one and not enough time before the masters to break/bet it in.
Hilarious what people make of it.
