Helmet strength.

It's also possible to tell by hitting it with a shovel a second time in
the same spot, and trust me you can hit the same spot over and over
hard with the edge of a shovel and you cannot get a mark on the GRP.
Indeed assuming the GRP in the helmet behaves the same way as GRP in a
boat (I bet it does) when if finally goes give way it will flex for a
while first keeping the polystyrene in situ.

I think you are seriously under estimating the strength and resiliance
of the outer shell of a helmet if you think a drop from normal drop
height will harm it.

 

Lurking.....;-)

 

Did you like the way I weaved that in to the discussion? It's amazing
where Materials Science lead one...ROFL

Ah! Isn't it just....;-)

 

But the critical damage won't necessarily show....

Well, I was jujst trying to point out some of the considerations;
you're quite free to disagree with them or ignore them, and what
decisions you make regarding these things are entirely up to you. It
isn't my head that's at risk ;-)

 

Right, this helmet had a bike fall on it.

By this stage you're arguing there would be critical damage the helmet
is now weak. (Indeed I thought that was the case which is why the
helmet was scrapped)

Then it was thrown at the ground as hard as poss.

*Then* it was hit hard with a shovel. About 100 times over the time I
was playing. I could barely mark it.

On that basis I would argue that no critical damage had been done at
all in that first stage of abuse. Indeed I wold argue that to weaken
the structure would take a significant blow that would be very visible.

Indeed given my experience of GRP in boats I'm strongly doubting that
'invisible' damage due to blows is even possible. The gel coat is so
weak relative to the GRP that there would always be signs.

Or trotting out the conventional propaganda?

Is there any evidence anywhere of a helmet that has been rendered
dangerously weak following a light blow, invisible on the helmet?

 

The helmet manufacturers say so.
In a circumstance where the padding material will not be compressed,
like it rolling off a bike seat, and there being little or no visible
external damage, my £20 says it's good as new.

I have broken the chin piece of two Arai. A Giga and an RX7RR. The first
in an MX off and the second in a track spill. It requires a highside
type free flight manoeuvre, I think after these two trial runs I have it
down pat <fx\ roll camera> I've never successfully split the main shell
of anything but an old (80's) Polycarb AGV.

Remember the toughness of the outer shell is also to do with abrasion
resistance, as Statto proved recently.

 

I always thought Kimberley Rew was a woman, til I went to a Soft Boys
gig.

 

That's where my money's going. Now I can fully understand how the
padding is a 'one use' deal (indeed every time you pull it over your
head you're reducing its effectiveness).

.....in contrast the shell appears to be pretty indestructable.

An interesting side issue is: Could you hit someone wearing a road
legal helmet with a shovel hard enough to kill them? I reckon you might
be able to. To prove it, all we need is a shovel, a helmet and John
Prescott.

 

Not if you understand material science. The material may age but gentle
compression below the yield point should have no effect.

Kill them? depends on the weight of the shovel I imagine. You can
certainly hit someone a glancing blow with a helmet (1) hard enough to
knock them sensless *and* shatter the wire reinforced glass door behind
;o)

(1) the helmet does not however remain serviceable, surprising and
upsetting.

 

WIth f**k all knowlege of physiology I reckon any and all of th eblows
I delivered would have damaged the helmet wearer - my first thought is
"wouldn't that just snap the neck?"

 

I reckon it was the edge of my helmet that broke my collarbone.
Perhaps the lower edge of helmets should be more padded or rounded.

 

I wasn't arguing anything. I was - or so I thought - showing what
mechanism lay behind the potential weakening and possible failure of
fibre-composite helmets; and that such weakening or failure was
difficult if not impossible to assess without expensive detection
equipment and expert analysis.

The military, especially when considering aerospace structures, are
extremely concerned about non-visible damage to structural composite
components, and have spent much time and effort searching for ways
merely to assess such damage.

I thought I was trotting out some Materials Science.

What you make of it is up to you.

A good question. I don't know, but I'm sure there are others on here
who might.

 

I think it you repeatedly hit it with a shovel and it always bounces
off you can say the weakening is *very* limited.

I'm not denying non-visible damage exists in some contexts. I'm saying
helmets are still very strong even after minor impacts.

That's why I asked.

 

Hog says...

I have, in the shop, so did one of my customers. The helmet in question
was an AGV Ti-Tech; yes, the same model as still used by one Valentino
Rossi. The then Arai rep showed me the fault, just pick the helmet up
and grab both sides of the chinstrap, pull them apart to compress the
cheekpads prior to pulling the helmet on and the shell would crack from
visor aperture to base of the chinbar on both sides. I demonstrated the
fault to a customer who insisted on trying one, it did exactly the same
thing when he tried to put one on.

At the time the Ti-Tech was the latest hot-poop helmet to come out of
any factory and Gericke UK had the first ones off the production line.
I'd only just put 24 of the things out on display, they all went back in
their boxes ready to be returned and I refused to sell them or any other
AGV helmet again.

 

One of my colleagues, who works on composites for aerospace
applications, tells me that the manufacturers are most worried about
technicians dropping things on the wing during maintenance. I'm with
Kim on this one.

 

I never bought another AGV either!!

 

It can be worse. One of my friends at Uni was called Kym, the more-
usual feminine spelling; he got lots of letters from the womens' clubs when
he turned up for Fresher Week.

--
Ivan Reid, Electronic & Computer Engineering, ___ CMS Collaboration,
Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN
GSX600F, RG250WD "You Porsche. Me pass!" DoD #484 JKLO#003, 005
WP7# 3000 LC Unit #2368 (tinlc) UKMC#00009 BOTAFOT#16 UKRMMA#7 (Hon)
KotPT -- "for stupidity above and beyond the call of duty".

 

Err, I've obviously missed this - what happened? Google link will do - can;t
seem to find anything meself.

 

Kiran says...

It's only Ogden, wgaf?

 

Not something I'll be describing in detail on ukrm. Catch me on MSN if
you're curious.