Question about non-conforming drivers

[bluedot]

I’m a bit confused.

 

I have read and been told that drivers, like aluminum baseball bats, lose some “pop” after long periods of use; 300-400 rounds is one number I’ve seen as a recommendation.  I follow that recommendation, at least in part because my son was a baseball player and we KNEW that aluminum bats lost some pop; HS and college players NEVER take their current gamer in the cage for this reason.  I have seen this when I get a new driver every couple of years, though it’s not huge, and I know a number of serious players who get a new driver every year because of this if they play tournament golf and practice a lot.

 

So now McIlroy and Scheffler, among others of lesser note, have had drivers ruled to be non-conforming after testing because of “CT Creep”, which is about the face becoming more flexible and the Characteristic Time increasing beyond the limits, increasing the trampoline effect of the face.

 

I’m having trouble reconciling the two pieces of information.  Scheffler said that he had been using his driver for a year, and that he knew it was probably close to being non-conforming, so does that mean the CT Creep is a completely separate process from a driver going “dead”, and that it happens only to high swing speed players?

 

As a related question, if we assume that the manufacturers all try to get their drivers to the “perfect” level of COR and face flex, etc, then does CT Creep automatically mean that the ball is going farther, even if only by tiny amounts?  Is it possible that changes in the face flex of a driver could actually make the ball go SHORTER, if only by tiny amounts, in the same way that low compression golf balls typically don’t go as far as higher compression premium balls?
 

By now, it may well be obvious that not only am I not a physicist, but that I didn’t even stay in a Holiday Inn Express last night.  

 

[Jeff58]

Aluminum and titanium are very different materials from a fatigue point of view. Titanium has no fatigue limit. As long as you don’t exceed its strength, or yield limit, it can be *cycled* to infinity. What is found is that the structure’s overall flex does tend to increase over use, and this change results in less distortion of the ball at impact, and therefore more potential ball speed.
 

Aluminum has a definite fatigue life, though different alloys vary. It tends to be very stable up to the point of failure, which can be catastrophic.

[Stuart_G]

28 minutes ago, bluedot said:

I’m a bit confused.

 

I have read and been told that drivers, like aluminum baseball bats, lose some “pop” after long periods of use; 300-400 rounds is one number I’ve seen as a recommendation. 

 

 

That really depends a lot on your swing speed.   That might be the number of rounds for pros but most am's can play the head for a MUCH longer period - maybe even indefinitely for slower swing speeds.    Although a lot of time with extra hard (and cold) range balls might shorten that life.

 

FYI - when OEM's test new designs they generally get tested for longevity by testing them with something like 10k impacts at higher speeds.

 

28 minutes ago, bluedot said:

I’m having trouble reconciling the two pieces of information.

 

If it helps, think of it as a two stage "failure".   

 

The first stage is for micro-fractures to cause the face to be a little bit weaker (without any actual plastic deformation) and flex more - this causes the COR to go up a little bit.    

 

When a head "looses it's pop" - it's usually a more severe and catastrophic failure - plastic deformation of the face that changes the bulge or roll or causes fat spots - or cracks in the weld seems - both of which will result in a noticeable loss in energy transfer to the ball.     Its' not impossible that there might be a short period where it's gradual but even then it doesn't usually last very long.  Once it starts it will usually drop off pretty fast.

 

So (IMO) no need to be overly cautious about switching heads - unless you're actually making a living from the performance.  When a head goes, you'll usually know it from the loss of distance.   It might even change the sound of impact.

 

Edited May 22 by Stuart_G

[dubbelbogey]

Qi10 (which both Scheffler and McIlroy are playing) are carbon-fiber faced drivers. Not titanium or any other metal.

 

Back a decade or so back, carbon fiber bats were really popular in youth baseball. A common effect was as the bat "broke in" it became hotter due to increased trampoline effect. The bats continued to get hotter as the carbon-fiber matrix broke in, up until some threshold where it broke down to the point of ultimately diminishing in performance. A cottage industry popped up to "roll" bats - effectively breaking them in to their hottest state without having to hit hundreds or thousands of balls to get the same effect. Soon, the regulating bodies caught on and banned this practice.

 

When TM came out with these carbon fiber faced drivers, I posted here asking if they'd ultimately have the same behavior. Well, we now have the answer - yes they do.

 

(Oh - and carbon fiber bats still exist, but standards were put in place to force the mfrs make the bats less amenable to this effect.)

 

Edited May 22 by dubbelbogey

[Stuart_G]

2 minutes ago, dubbelbogey said:

Well, we now have the answer - yes they do.

 

The specific material doesn't really matter all that much.  

 

Anytime you minimize the weight of an impact device, it means you'll be pushing the structural strength to it's lower limits for the intended use.  So that strength will pretty much always be a vulnerability.

[dubbelbogey]

34 minutes ago, Stuart_G said:

 

The specific material doesn't really matter all that much.  

 

Anytime you minimize the weight of an impact device, it means you'll be pushing the structural strength to it's lower limits for the intended use.  So that strength will pretty much always be a vulnerability.

Yes, but my point was more that carbon fiber has the behavior of getting significantly "hotter" as it breaks in relative to aluminum and titanium, which do not (or no nearly to such a significant degree.) When an aluminum bat breaks down, it just gets slower.

 

Scheffler and McIlroy's clubs were deemed non-conforming because they exceeded the CT spec - i.e. performed at a level that exceeded what was allowed. If they just broke down and degraded (became slower), I think the ruling bodies wouldn't care at all. 

[Stuart_G]

32 minutes ago, dubbelbogey said:

Yes, but my point was more that carbon fiber has the behavior of getting significantly "hotter" as it breaks in relative to aluminum and titanium, which do not (or no nearly to such a significant degree.) When an aluminum bat breaks down, it just gets slower.

 

That's because aluminum generally has a much lower yield strength.  Those types of materials wouldn't be suitable for a driver face.  At least not anymore in any new material chosen to try and replace titanium.   It was tried back in the 70's and 80's but never really worked out because of the low yield strength.

Edited May 22 by Stuart_G

[Jeff58]

59 minutes ago, dubbelbogey said:

Yes, but my point was more that carbon fiber has the behavior of getting significantly "hotter" as it breaks in relative to aluminum and titanium, which do not (or no nearly to such a significant degree.) When an aluminum bat breaks down, it just gets slower.

As @Stuart_G is pointing out, they don’t get “hotter”, they become more flexible without failing. Aluminum behaves differently, and for an application where repeated stress is a key component, isn’t an appropriate solution. Although CF forms may initially have similar characteristics to Ti, what is changing (and actually breaking down), is the resin rather than the CF itself. Eventually it will fail where an optimal Ti solution would not.

[jcvandamme]

3 hours ago, dubbelbogey said:

(Oh - and carbon fiber bats still exist, but standards were put in place to force the mfrs make the bats less amenable to this effect.)

 

I have nothing to add to this conversation other than to say your abbreviation of the word "manufacturers" made me think something totally different...

[PostandGhost]

2 hours ago, Stuart_G said:

 

That's because aluminum generally has a much lower yield strength.  Those types of materials wouldn't be suitable for a driver face.  At least not anymore in any new material chosen to try and replace titanium.   It was tried back in the 70's and 80's but never really worked out because of the low yield strength.

If I recall correctly, the last driver that used an aluminum face was the Mag Cruzer from the mid 2000's.  The body was magnesium and I'm fairly certain the face was aluminum.  That thing was so dang light they needed 60 grams of tungsten weights just to get it close to 200 grams.  De La Cruz loved some aluminum.  I think he used it on his Goldwin ADVP woods as well.  

[dubbelbogey]

If interested, I would encourage one to go and do their own honest research into this. For baseball bats, it's pretty well accepted consensus that a composite (carbon fiber in a resin matrix, with or without other reinforcing fibers such as fiberglass, kevlar, other aramids, etc...) do, in fact, get "hotter" as they break in. You can call this "getting softer without failing" - or give it any other name you'd like. The point is the ball flies faster and farther off such a bat (given the same impact conditions) than off a brand new bat that has not undergone this transition.

 

But, to kick off the search for those interested, here's one paper out of Penn State University:

https://www.acs.psu.edu/drussell/bats/abi.html

 

Now, I'm the one making the assumption that a carbon-fiber golf driver face will behave in an analogous manner to that of a carbon fiber baseball bat. I fully admit I have no proof of this at this time (relative to golf clubs), but it seems a reasonable assumption given that Scheffler's and McIlroy's (old) drivers both failed the CT limit test, and the technology in these clubs is substantially similar to carbon fiber bats. To "fail" the CT test means that a ball would likely fly faster and farther off said club than one that is conforming. The driver face has become more springy (or hotter, if you prefer) over time due to repeated hitting of a golf ball. Failure here does not mean the face has undergone some sort of full structural failure. 

 

Let's take aluminum completely out of the conversation here - it's not used in drivers anymore, so it's not really relevant other than the one important fact that carbon fiber does not behave like aluminum over time.

[bluedot]

10 hours ago, dubbelbogey said:

If interested, I would encourage one to go and do their own honest research into this. For baseball bats, it's pretty well accepted consensus that a composite (carbon fiber in a resin matrix, with or without other reinforcing fibers such as fiberglass, kevlar, other aramids, etc...) do, in fact, get "hotter" as they break in. You can call this "getting softer without failing" - or give it any other name you'd like. The point is the ball flies faster and farther off such a bat (given the same impact conditions) than off a brand new bat that has not undergone this transition.

 

But, to kick off the search for those interested, here's one paper out of Penn State University:

https://www.acs.psu.edu/drussell/bats/abi.html

 

Now, I'm the one making the assumption that a carbon-fiber golf driver face will behave in an analogous manner to that of a carbon fiber baseball bat. I fully admit I have no proof of this at this time (relative to golf clubs), but it seems a reasonable assumption given that Scheffler's and McIlroy's (old) drivers both failed the CT limit test, and the technology in these clubs is substantially similar to carbon fiber bats. To "fail" the CT test means that a ball would likely fly faster and farther off said club than one that is conforming. The driver face has become more springy (or hotter, if you prefer) over time due to repeated hitting of a golf ball. Failure here does not mean the face has undergone some sort of full structural failure. 

 

Let's take aluminum completely out of the conversation here - it's not used in drivers anymore, so it's not really relevant other than the one important fact that carbon fiber does not behave like aluminum over time.

Good post; thank you!

[cristphoto]

"That really depends a lot on your swing speed.   That might be the number of rounds for pros but most am's can play the head for a MUCH longer period - maybe even indefinitely for slower swing speeds.    Although a lot of time with extra hard (and cold) range balls might shorten that life".

 

I knew there were benefits to getting older. ☺