Helmet quality and longevity

For all discussions about this "lively" subject. All topics that are substantially about helmet usage will be moved here.
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Mick F
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Re: Helmet quality and longevity

Postby Mick F » 13 Sep 2013, 8:39am

Steady rider wrote:About 4.8 kg roughly.

How heavy! :shock:

Steady rider wrote:Any vehicles approaching from the rear may have noise frequency similar to the vibration frequency/level of your straps and you may be less aware compared with someone without a helmet. Perhaps a minor disadvantage and hopefully will not be significant. ps I was first told about helmet strap noise back in about 1991.
I can assure you that the "noise" wasn't a noise that would interfere with my hearing of vehicles behind. And so what if it did? They're behind me and therefore of no interest and like you say, maybe insignificant. If I wanted to turn right, I'd look back and/or look in my mirror.

By the time I'm doing fast enough for the vibration to start, there are loads of other noises going on. Wind in the ears for one thing.

As I said, I should be able to fix this. It's only a matter of damping out the resonance. Sticky tape or a lazzy band should do it.

Off out soon for a ride - maybe get wet, as it's raining a tad. I'll fit a small lazzy band before I leave. Yesterday, I was in no mood for stopping and sorting, I just kept going. By turning my head so I was "left eye leading" the vibration stopped completely. I'm very much in the "right eye leading" camp so it took a conscious decision to move my head slightly.

Off soon for a test of the lazzy band.
Mick F. Cornwall

MartinC
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Re: Helmet quality and longevity

Postby MartinC » 13 Sep 2013, 8:42am

Mick, by now your old helmet must've saved your life (and possibly many others) millions of times. Making a hanging basket out of it shows an alarmimg lack of respect and it's almost certainly not certified for this use. You should attach it to your bike where it can still work it's magic alongside the new one. If one helmet is good then two must be better, you know it makes sense.

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Re: Helmet quality and longevity

Postby Steady rider » 13 Sep 2013, 9:12am

Perhaps they should be mounted on the wall, saved my life 4 times, 6 times, etc.

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Mick F
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Re: Helmet quality and longevity

Postby Mick F » 13 Sep 2013, 11:57am

The things I do for science! :lol:

Take a bucket big enough to contain one's head, and a large measuring jug.
Fill the bucket to the very brim with tepid water.
Take a deep breath and hold it.
Place one's head slowly right into the bucket and don't move.
Count to ten.
Remove one's head gently allowing the drips and excess water to return to the bucket.
Breath normally again.
Measure how much water is required to fill the bucket to the brim again.
This amount of water will equal one's head volume.
Bucket and Jug.JPG
Bucket After.JPG
My head came out as 3850cc ie 3.85Kg if it were 100% water. ie the maximum weight possible for my head.

Next, take a carrier bag and fill with sand and gravel to weigh 4Kg. ie in excess of the weight of my head.
Place it neatly inside an old helmet.
Drop the whole lot - helmet top downmost - onto a solid floor. I used head-height onto solid concrete.
Repeat until there is something to report.
Helmet Before.JPG
Sand and Gravel.JPG
Helmet After 1.JPG
Helmet After 2.JPG
I dropped the helmet three times from head-height. The first two times it bounced and appeared undamaged.

Third time I dropped it, it landed with a thud.
I didn't try a fourth.
Other than the dents you can see on the top, there appears to be only a small crack on the inside near the outer dent. This crack has destroyed the integrity of the shell and that's why it didn't bounce on the third drop. I suppose I could keep dropping it to see what happens, but it would serve no purpose as all it would do would be to become increasingly dented and the crack migrate. There isn't a hope of it cracking up completely or doing anything spectacular.
Internal Crack.jpg


To be honest, I'm actually impressed!
That was one heck of a drop with a dead weight inside far heavier than my head.
Yes. Impressed. :D
Mick F. Cornwall

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Re: Helmet quality and longevity

Postby Vorpal » 13 Sep 2013, 12:33pm

Mick F wrote:The RH strap vibrated and "buzzed" at anything over 25mph.
Maybe I can sort this out.


I have a Specialized S-Works that did this. The little clip (I don't know if it has a proper name) that joins the two parts of the 'Y' into a single strap on each side can be moved up & down, and I moved mine as close to my ear lobe as I could & still get the helmet on & off without adjusting it each time. Of course the two straps that run together from that clip must be as close together as possible. The correct length will vary between people & I suspect that there is a particular length that is critical to set up the buzz at speed. So, your solution may not be identical to mine, but I think that minor adjustment of that clip may solve the problem.
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Re: Helmet quality and longevity

Postby MartinC » 13 Sep 2013, 12:42pm

Mick, well done on your experiment. You skillfully avoided asking for any feedback about your head density! :D

Not sure what you're impressed by though - presumably the bag of sand's cognitive ability was much less damaged by the impact with the helmet as compared to that without. Nevertheless I think you've proved conclusively that plastic carrier bags have a major protective effect and wearing them (all over) should be mandatory for cycling.

Anyway, don't tell Mrs Mick 'cos you've just proved that you didn't need to spend £75 on a new helmet.

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Re: Helmet quality and longevity

Postby BeeKeeper » 13 Sep 2013, 12:44pm

I would nominate MickF for an honorary degree if it was in my power for pushing forwards the boundaries of science.

For some reason his experiment reminded me of a story from Afghanistan. A soldier kept having "bright ideas" but they always misfired. To cure him his colleagues invented the Bright Ideas Removal Tool.

This consisted of two foot-shaped outlines drawn on the ground about a foot from a wall. At shoulder height and width apart two hand prints were drawn on the wall and between them a cross was painted.

To use the tool the person with the bright idea was made to stand on the footprints, place their hands on the marked spots on the wall and then hit their head on the cross repeatedly until the Bright Idea was removed. I am not sure if the tool would be more efficient if the person was wearing a cycle helmet but it would be interesting to experiment!

More seriously, Mick's experiment shows why you are supposed to replace a helmet after a fall. They don't take repeated blows. It proves nothing to the helmet sceptics of course but interesting nonetheless.

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Mick F
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Re: Helmet quality and longevity

Postby Mick F » 13 Sep 2013, 1:26pm

BeeKeeper wrote:More seriously, Mick's experiment shows why you are supposed to replace a helmet after a fall. They don't take repeated blows. It proves nothing to the helmet sceptics of course but interesting nonetheless.
+1
That's what I was inferring. Can't take repeated blows and an interesting experiment.

It impressed me how much punishment that helmet took before any damage.
Had I stopped after the first drop, we would be none the wiser.
I reckon it would take a dozen drops more before the thing started to fall apart.

Remember, the sand and gravel bag was 4Kg of dead weight. My head is 3850cc with perhaps 70% water and a few percent empty nasal and breathing cavities, my head may weigh as little as 2.5Kg. Maybe if I'd used only 2.5Kg of sand and gravel, I could still be outside now continually dropping it waiting for something to happen.

As I said, I'm impressed.

--------------------------------------------------------------
BTW, my lazzy band on my new helmet strap did nothing.
Why?
Coz I put it in the wrong place! :oops:

The straps on the helmet aren't adjustable on the sides, only under the chin. They have a simplified the Y shape and it's fixed rather than adjustable. It was the front of the RH Y that vibrates. I thought it was the main strap vibrating - I was wrong.

Next time out, I'll try something else.
Mick F. Cornwall

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Re: Helmet quality and longevity

Postby snibgo » 13 Sep 2013, 1:38pm

Good stuff, Mick.
Mick F wrote:Place one's head slowly right into the bucket and don't move.

I really want to see that video!

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Mick F
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Re: Helmet quality and longevity

Postby Mick F » 13 Sep 2013, 2:25pm

I had a few problems with photographing it all.

1. I'm home alone.
2. I could have used my tripod and the camera on timer, but my tripod is with Daughter1 in Manchester.

and mainly ......

3. I was "rather undressed" and outside on the decking! :oops:
Great way to cool off from a ride. :D
Mick F. Cornwall

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Re: Helmet quality and longevity

Postby [XAP]Bob » 13 Sep 2013, 2:27pm

If your head is hitting with the crown to a flat surface then you'd have your whole body weight behind it
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

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Mick F
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Re: Helmet quality and longevity

Postby Mick F » 13 Sep 2013, 2:33pm

Yes, true.

If I were dropped on my head, no doubt there's be damage to the rest of my body especially my spinal column too - let alone my surface of my skull.

I thought about how I could do a simple test, and dropping it was simple. In effect, it simulated a very heavy header over the 'bars.
Mick F. Cornwall

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Re: Helmet quality and longevity

Postby snibgo » 13 Sep 2013, 3:05pm

Yeah, on balance, perhaps I'm happy not to see that video.

That's a good bit of work, Mick. The bouncing is interesting -- it shows that something is deforming (stretching or compressing) to absorb energy, then returning to its previous state, which releases energy. The "something" is expanded polystyrene, or the cradle, or both. Probably mostly the EPS.

Ideally, for a single collision, we would want the EPS to compress but then not return. We don't want our heads bouncing up and down like a ping-pong ball. The EPS should compress and stay compressed. However, this would compromise the helmet's ability to withstand a second blow in the same accident.

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Re: Helmet quality and longevity

Postby Steady rider » 13 Sep 2013, 3:12pm

The sort of mean value quoted in reports for adult head mass is about 4.8 kg, so either the reports are possibly wrong or some aspect needs clarification.

wiki seems to be out by a mile, http://en.wikipedia.org/wiki/Human_head 5-30 lbs - (5kg is about 11 lbs)

In impact tests 8.5m/s onto a 15% slope, they reported a wide range of findings for linear acceleration and rotational accelerations. In all cases both types of forces existed. Your experiment probably produced linear accelerations due to sand spreading over the inside shape and distributing the forces and a straight drop. So you probably produced the minimum forces for fracturing EPS. EPS is good on compression that you effectively tested for but poor in tensile. If you have forward motion it produced both linear and rotational forces on impact, e.g. more likely to fracture the material.

Most impacts occur near the test line, very few on the crown.
Last edited by Steady rider on 13 Sep 2013, 3:22pm, edited 1 time in total.

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Re: Helmet quality and longevity

Postby MartinC » 13 Sep 2013, 3:17pm

Hmmmm. It's all very interesting but the thing that matters is the effect on the thing in the helmet not the effect on the helmet. They're supposed to work through crushing absorbing energy and decreasing the peak acceleration passed on to the contents. Without an accelerometer in the contents it's hard to know what's going on. That the helmet didn't break is good but the absence of crushing does make one wonder how much it attenuated the acceleration. It's in line with teh published concerns of the Bell helmet engineer who was wondering if the testing regime was creating a tendency for modern helmet to be too hard to cushion lower intensity blows.