Helmet strength.

The SO's helmet got the full weight of her bike on it when the wind
blew her bike over whilst the lid was hanging on the bar end.

It knocked a load of gelcoat off and it looked like the fibre glass
might have been manky so she figured it was time for a new lid.

I expect you can guess where this is going.

We took the old lid into the Garden just now with a shovel.

First we threw it hard at the patio from a couple of feet.

No damage.

Then we 'applied' the flat of the shovel.

No damage - but the shovel vibrated uncomfortably.

Getting mean we used the edge of the shovel.

Easy to mark a line in the gel coat with the edge but the SO couldn't
mark the fibre glass at all.

Next we went for a frontal jab to the visor - disappointment - it just
cracked to bits - leaving some sharp edges.

Now my turn. I just went for it with the edge of the shovel. I found it
easy enough to chip gel coat but I could barely mark the fibre glass.

The one way we found to gouge the gel coat was by getting contact with
the corner of the edge of the shovel. Even then were talking about
1-2mm of depth and no way could you expect to penetrate the helmet even
with multiple strokes to the same spot.

I won't be fretting about a dropped helmet ever again - those things
are seriously strong - the idea of a drop weakening them in a
meaningful way is a joke.

 

A pick will get through a helmet. A UK legal air rifle won't.
I'd be interested to know what calibre/velocity of bullet would.
Perhaps someone in rec.motorcycles has tried it. (Cross posted)

 

The damage isn't so much about the shell getting a knock, it's about the
foam inside it becoming compressed so the helmet no longer softens the
impact rather than transfering it straight to the skull.

Although in your case there might be a perfectly valid reason not to
worry about that kind of thing...

 

Using the patented Mavis Beacon "Hunt&Peck" Technique,
typed

The damage you should worry about is to the liner, not the shell.

HTH

--
Wicked Uncle Nigel - Podium Placed Ducati Race Engineer As featured in
Performance Bikes

WS* GHPOTHUF#24 APOSTLE#14 DLC#1 COFF#20 BOTAFOT#150 HYPO#0(KoTL) IbW#41
SBS#39 OMF#6 Enfield 500 Curry House Racer "The Basmati Rice Burner",
Honda GL1000K2 (On its hols) Kawasaki ZN1300 Voyager "Oh, Oh, It's so big"
Suzuki TS250 "The Africa Single" Yamaha Vmax Honda ST1100 wiv trailer

 

How can the drop damage the 'foam'? I can see how that becomes
compressed in normal use (putting it on and taking it off) but not from
a dropped empty helmet.

I've still got the helmet here. Are you telling me if I hacksaw a cross
section out I will notice thinner 'foam' where the harder blows hit?

I went to a Shoei presentation where we were shown the cross section
etc and we were told that the reason you need to replace dropped
helmates was deformation of the GRP layer, not the foam.

 

Sure, try cutting through where the bar end hit the inside.

 

If you think about it, a helmet that craps out after a three-foot fall
wouldn't have been any good at protecting your noggin anyway.

 

And so another gun thread thunders its way skywards...

 

The Nitro lid I bought earlier this year survived a crash without much
superficial damage, but the whack on the head left me unconscious for a
good few minutes. I'm not sure of the details (a bang on the head not
being great for the memory), but think I hit the back of my head after
the bike went over on its side, so it wasn't a phenomenally hard whack.
The visor parted company with the helmet pretty much straight away, and
somehow I (or somebody, my memory is non-existant) managed to get the
lid off without undoing the strap, despite the lid itself being a good
fit.

Not the most scientific test, but I'd have to think hard before buying a
cheap lid again.

 

..22 or bigger.......the head shot is the only true stopper.

 

Try repeating the tests when wearing the helmet while your SO wields the
shovel...

 

Try repeating the tests when wearing the helmet while your SO wields the

lol

 

Sir requires a powerful beast ...

http://www.swissminigun.com/img/rev_main.jpg

http://www.swissminigun.com/home.html

That's the right tool for the job

 

ogden says...

<Nitro sales rep hat (helmet) on>

A helmet is designed to absorb two main shocks with a view to
eliminating a third altogether. The initial shock is your helmet hitting
tarmac. The outer shell absorbs this by deforming and thereby spreading
the biggest shock of all round a larger area of the helmet, which is why
they are made of pretty tough but reasonably flexible materials. The
second shock is your head hitting the inner of the helmet, because your
head will move a significant amount during this impact. The inner
polystyrene liner takes care of this by compressing in the area of
impact, which is why liners are made from expanded polystyrene foam with
varying densities in crucial places. Once these impacts have been taken
care of the next job is protecting yor brain from hitting the inside of
your skull, and that's down to you having sufficient cerebral fluid to
absorb whatever movement is left.

A sharp shock, such as the one you had to the back of the head will be
sufficient to render many people unconcious, helmet fitted or not.

I've seen visors from many different helmets fly off in accidents.
Unfortunately designing a foolproof and unburstable visor mech is almost
impossible without making it over-large, complex, heavier and unwieldy.
Motorcyclists demand ease of visor removal nowadays, which means there
has to be a compromise somewhere. In normal use a visor stays put, but
I've been witness to Arai visors flying off in normal useage, Zymurgy
and at least one other person had this happen at Mallory a couple of
weeks ago. Ditto Shoei, AGV etc etc, they all do it.

This is down to you not doing basic tests before buying a helmet. One of
the things I was always told to do was to try and remove the helmet when
it was all strapped up tight. There are very few helmets that pass this
test with my head. IIRC you bought an N800-V, which is one of the
helmets I can wear safely. Next time you buy a helmet try the removal
test, you'll possibly find that a fair few aren't suitable. Helmet
manufacturers have to make helmets to fit a wide variety of head shapes,
and not all nitros will be suitable, nor will all Arais, or Shoeis. I
know this because of the current Arai range only the two cheapest models
stay on my head when I do the removal test in the shop. Some of the
others don't fit anywhere comfortably on my head at all.

My friend Neil Tyers died when his helmet fell off his head in a 30mph
impact with a car's windscreen surround. He died when he landed head
first on the tarmac on the other side of the car. For weeks I'd been
having a go at neil for never strapping his helmet up, and the night he
died was the only time any of us can remember him ever doing it up. I
tried his FM helmet on after he died, in front of a traffic copper, it
rolled straight off my head with no effort needed.

I wouldn't blame the cheap lid, I'd blame your choice of cheap lid. You
might have found that a £50 N510-V fits you far better, or you might
have had to go for the slightly more pricey N750-VX. Obviously they all
pass the same safety tests, but it's a matter of whether they are
suitable for your particular head shape that matters.

 

wrote:

This is what I understand. If you're wearing it your head compresses
the polystyrene, if its empty the possibility of the fibreglass popping
in and out, compressing the foam with no visible damage.

I would just take it apart and look. They're not rocket science.

 

How do you do this? I presume you try to roll the helmet forward
by pushing up from the rear[1] to see if it is possible for the helmet
to come off.

[1] fnarr!

 

That. Coupled with the fact my Shark lid is shit. The visor retainers
are not that good, and the fact that one of the catches was run over in
France the first time the visor blew off, means that it's a bit weak
when the visor is open (but fine when closed)

New lid time, but i've been trying several on over the last couple of
months, and the new Shoei's don't fit as well as my old XR800, and the
Arai's aren't a wonderful fit either.

As soon as I find something comfortable, i'll relegate it to the spare.

P.

 

What sir needs is a sledge hammer.

Or an axe.

Both worked a treat when I 'de-commissioned' a helmet that had gone
mouldy on the inside.

 

I'm not sure whether your former helmet used glass-fibre or
carbon-fibre as the base material, but they behave in the same way,
which essentially means it gets its impact strength from the fracture
of many thousands of fibres that make up the composite structure.

High-strength (structural) fibres tend to be a few microns in
diameter, and have individual breaking loads of a few grams each. But
spread the impact load over a hundreds of thousands of fibres, and the
effective strength of the structure (helmet in this case) becomes
obvious.

Note that the function of the resin matrix material is to transfer the
impact load to as many fibres as possible - its own strength is far
less than that of the fibres.

The implications of this is that while the outer surface may appear to
have light damage, it is almost impossible to tell without
highly-sophisticated devices whether any significant fibre damage has
occurred. This means that there is a risk involved in using such a
helmet , as there is no effective way of assessing any damage.

Another problem is the lay-up of the fibres. The maximum fibre
strength is obtained when all the fibres lay in one direction only
('unidirectional'). For aerospace applications sheets of
unidirectional fibres are laid-up at precise angles to each other, as
computed by the expected stress directions in service, and are then
bonded together.

But to make a three-dimensional structure such as a helmet, other
properties are required, one of these being 'drape'. To obtain 'drape'
the fibres are woven into cloths, and there are very many weave
patterns each with their own characteristics. One gives maximum drape,
called tricot weave. Women's underwear is largely tricot weave, for
much the same reason.

But the act of weaving a cloth means that the fibres are now no longer
'unidirectional', and so have lower strengths. This means that in a
loaded situation (such as the bike falling on the helmet) or an impact
situation (as mentioned) many more fibres are going to fracture due to
individual stress levels being raised.

But little of this is visible to the naked eye. Although it might seem
to be over-reacting, the advice about replacing compromised but
seemingly-undamaged helmets is IMHO, sensible, as is the advice of the
poster who mentioned the 'take-off' test before buying a replacement.

 

Sensible, well informed and polite...


What the **** are you doing here?