Oh no, not again!

[Zust Zis Guy]

"Cletus D. Lee" <[email protected]> wrote in message
news:[email protected]...

> Do you think you could document those astute counter
> points with some substantiated facts?

As I understand it there is an article due for publication
soon which describes the way in which helmets are supposed
to work. They are supposed to absorb energy by plastic
deformation - polystyrene absorbs very little energy in
brittle failure (which is why they introduced the kerb-edge
test, because so many helmets were cracking open and not
working at all when hitting kerb edges). The old Snell
standards (as used when Thompson, Rivara and Thompson
produced their first study) were also much stricter than the
standards used for modern vented helmets. As an aside, if
you replace TR&T's control group with the street counts
conducted by Rivara on the streets the year before, the
"protective effect" vanishes entirely; the control group
they used was middle class white families riding on bike
trails, but the case group was mainly street cyclists. This
may explain why nobody, including TR&T, has subsequently
been able to duplicate the result.

I will post the contents of the helmet article when
published.

--
Guy
===
May contain traces of irony. Contents liable to settle after
posting. http://www.chapmancentral.co.uk

88% of helmet statistics are made up, 65% of them at
Washington University

 

[Zust Zis Guy]

"Prints" <[email protected]> wrote in message
news:%[email protected]...

> Is this fault due to lack of heat treatment? I understand
> that aluminium welding requires heat treatment after
> welding to dissipate the stresses
that
> cause cracks.

I dunno. All I can tell you is: it's bust agin.

--
Guy
===
May contain traces of irony. Contents liable to settle after
posting. http://www.chapmancentral.co.uk

88% of helmet statistics are made up, 65% of them at
Washington University

 

[Tom Sherman]

Zust zis Guy, you know? wrote:

> "Prints" <[email protected]> wrote in message
> news:%[email protected]...
>
>
>>Is this fault due to lack of heat treatment? I understand
>>that aluminium welding requires heat treatment after
>>welding to dissipate the stresses
>
> that
>
>>cause cracks.
>
>
>
> I dunno. All I can tell you is: it's bust agin.

Without examining the failure surface one can only speculate
as to the cause of the failure, but the most probable is
fatigue. The junction of the head and main tubes will be
subject to repetitive loads while riding, and if these loads
are more than a small fraction of the yield strength [1] of
the material, crack propagation and failure will occur after
relatively few loading cycles (1000 miles worth in the case
of Guy's bike).

The corrective action would be to use a material that has a
fatigue limit well above the stresses encountered in normal
use (such as steel or titanium alloy) or to redesign the
frame to reduce stresses in the failure area (which Optima
did with the gussets on the second generation Baron frame).

[1] This depends on the exact aluminium alloy used and its
heat treatment/aging.

Tom Sherman - Quad Cities (Illinois Side)

 

[Dave Larrington]

Zust zis Guy, you know? wrote:

> "W K" <[email protected]> wrote in message
> news:[email protected]...
>
>> Mildly surprised they let you on with it. Much more
>> surprised that you got on with it in the morning.
>
>
> Heh! You've been reading the Nugentoid of Kager IV
> again ;-)
>
> No bike restrictions on Thames Trains heading away from
> London in the mornings. I go from Reading to Didcot
> Parkway.

Apropos which, anyone know about the (im)possibility of
taking a recumbent trike by train from Kings X to Hull?

[waits expectantly]

--

Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/
===========================================================
Editor - British Human Power Club Newsletter
http://www.bhpc.org.uk/
===========================================================

 

[Tom Sherman]

Cletus D. Lee wrote:

> ... (I'll let Mikael skate for a while since he's a Dane
> and what do Danes know?)

How to raid and pillage Great Britain.

Tom Sherman - Quad Cities (Illinois Side)

 

[Graeme]

"harv" <[email protected]> wrote in news:[email protected]:

> If you bring in a cracked skull, will they give you a
> new head?
>

I've just realised that although I wear a cycling helmet,
when I was a kid I had many thumps and whacks to my head
(including a smack with a hammer), many of them greater than
those which have wrecked my last few helmets. Other than the
odd cut, none of them had any permanent measurable effect. I
now have visions of my head being hung outside a police
station, hunting trophy style :-/

Graeme

 

[Dave Kahn]

"Mikael Seierup" <[email protected]> wrote in message news:<[email protected]>...
> "Dave Kahn" skrev
>
> > Unfortunately the smashed helmets have all failed. If
> > the riders were not hurt in their various accidents this
> > indicates that the helmets failed in minor collisions.
>
> No idea why I bother but helmets are supposed to break.
> Thats whats absorbs the energy and keeps your noggin in
> one piece.

This is a common misconception in spite of your patronising
tone. The energy absorption is achieved through plastic
deformation of the foam. Brittle failure of the helmet
structure absorbs very little energy. In the section on
impact test interpretation the Snell B-90A standard states:
"The peak acceleration of the headform shall not exceed 300
G's for any valid test impact. Similarly, the helmet's
protective structures shall remain intact throughout the
testing. If, the Foundation's technical personnel conclude
that the headgear has been compromised by breakage, the
sample shall be rejected."

--
Dave...

 

[Just Zis Guy]

"Tom Sherman" <[email protected]> wrote in message
news:[email protected]...
> Zust zis Guy, you know? wrote:

> Without examining the failure surface one can only
> speculate as to the cause of the failure, but the most
> probable is fatigue.

It is a classic fatigue failure, looking at it, as the last
one was. Whether this would have been mitigated by better
heat treatment I couldn't say.

--
Guy
===
May contain traces of irony. Contents liable to settle after
posting. http://www.chapmancentral.co.uk

88% of helmet statistics are made up, 65% of them at
Washington University

 

[Jack Davis]

Let me see if I have this right....

You "now have visions of [your] head being hung outside a
police station", but none of the "thumps and whacks to
[your] head (including a smack with a hammer)", have "had
any permanent measurable effect." ???

Well, OK then... aren't you lucky. :}

Just so you're having fun...

JD

"Graeme" <[email protected]> wrote in message
news:[email protected]...
> "harv" <[email protected]> wrote in
> news:[email protected]:
>
> > If you bring in a cracked skull, will they give you a
> > new head?
> >
>
> I've just realised that although I wear a cycling helmet,
> when I was a kid I had many thumps and whacks to my head
> (including a smack with a hammer), many of them greater
> than those which have wrecked my last few helmets. Other
> than the odd cut, none of them had any permanent
> measurable effect.
I
> now have visions of my head being hung outside a police
> station, hunting trophy style :-/
>
>
> Graeme

 

[Jack Davis]

Let me see if I have this right....

You "now have visions of [your] head being hung outside a
police station", but none of the "thumps and whacks to
[your] head (including a smack with a hammer)", have "had
any permanent measurable effect." ???

Well, OK then... aren't you lucky. :}

Just so you're having fun...

JD

"Graeme" <[email protected]> wrote in message
news:[email protected]...
> "harv" <[email protected]> wrote in
> news:[email protected]:
>
> > If you bring in a cracked skull, will they give you a
> > new head?
> >
>
> I've just realised that although I wear a cycling helmet,
> when I was a kid I had many thumps and whacks to my head
> (including a smack with a hammer), many of them greater
> than those which have wrecked my last few helmets. Other
> than the odd cut, none of them had any permanent
> measurable effect.
I
> now have visions of my head being hung outside a police
> station, hunting trophy style :-/
>
>
> Graeme

 

[Patrick Herring]

"Mikael Seierup" <[email protected]> wrote:

|
| "Cletus D. Lee" skrev...
|
| Dave Kahn blurted...

Actually that was me blurting...

| > > No it isn't.
|
| http://www.bhsi.org/henderso.htm 4.5 and 4.6

You may be confusing "It is the liner of the helmet that is
responsible for absorbing the energy of impact through its
own destruction." with the whole helmet being broken.
"destruction" here means "being crushed to absorb energy
that would otherwise deform your skull", and the outer shell
keeps the inner foam in place in order that it does that,
which it won't if it breaks.

However, there are helmets with no outer shell. To me that
just emphasises how little protection bike helmets are
intended to give.

| Oh, yes it is. You just ride without one though. Ride like
| the wind, Sonnyboy, and take lots of chances.

I don't ride like the wind & I take as few chances as I can.

| Oh wait, maybe you already did. Yea, that sure explains a
| lot. ;o)

<twitch><twitch>

--
Patrick Herring, Sheffield, UK http://www.anweald.co.uk

Eala Earendel engla beorhtast ofer middangeard monnum
sended.

 

[Patrick Herring]

"Mikael Seierup" <[email protected]> wrote:

|
| "Cletus D. Lee" skrev...
|
| Dave Kahn blurted...

Actually that was me blurting...

| > > No it isn't.
|
| http://www.bhsi.org/henderso.htm 4.5 and 4.6

You may be confusing "It is the liner of the helmet that is
responsible for absorbing the energy of impact through its
own destruction." with the whole helmet being broken.
"destruction" here means "being crushed to absorb energy
that would otherwise deform your skull", and the outer shell
keeps the inner foam in place in order that it does that,
which it won't if it breaks.

However, there are helmets with no outer shell. To me that
just emphasises how little protection bike helmets are
intended to give.

| Oh, yes it is. You just ride without one though. Ride like
| the wind, Sonnyboy, and take lots of chances.

I don't ride like the wind & I take as few chances as I can.

| Oh wait, maybe you already did. Yea, that sure explains a
| lot. ;o)

<twitch><twitch>

--
Patrick Herring, Sheffield, UK http://www.anweald.co.uk

Eala Earendel engla beorhtast ofer middangeard monnum
sended.

 

[Dave Kahn]

"Mikael Seierup" <[email protected]> wrote in message news:<[email protected]>...
> > Dave Kahn blurted...
> > > > No it isn't.
>
> Ooops... Patrick Herring of course. Sorry, Dave.

Yes, you do seem a bit confused.

--
Dave...

 

[Dave Kahn]

"Mikael Seierup" <[email protected]> wrote in message news:<[email protected]>...
> > Dave Kahn blurted...
> > > > No it isn't.
>
> Ooops... Patrick Herring of course. Sorry, Dave.

Yes, you do seem a bit confused.

--
Dave...

 

[Jack Davis]

"Patrick Herring" <[email protected]> wrote in message
news:[email protected]...
> "Mikael Seierup" <[email protected]> wrote:
>
> |
> | "Cletus D. Lee" skrev...
> |
> | Dave Kahn blurted...
>
> Actually that was me blurting...
>
> | > > No it isn't.
> |
> | http://www.bhsi.org/henderso.htm 4.5 and 4.6
>
> You may be confusing "It is the liner of the helmet that
> is responsible for absorbing the energy of impact through
> its own destruction." with the whole helmet being broken.
> "destruction" here means "being crushed to absorb energy
> that would otherwise deform your skull", and the outer
> shell keeps the inner foam in place in order that it does
> that, which it won't if it breaks.
>
> However, there are helmets with no outer shell. To me that
> just emphasises how little protection bike helmets are
> intended to give.
>
> | Oh, yes it is. You just ride without one though. Ride
> | like the wind, Sonnyboy, and take lots of chances.
>
> I don't ride like the wind & I take as few chances
> as I can.
>
> | Oh wait, maybe you already did. Yea, that sure explains
> | a lot. ;o)
>
> <twitch><twitch>
>
> --
> Patrick Herring, Sheffield, UK http://www.anweald.co.uk
>
> Eala Earendel engla beorhtast ofer middangeard
> monnum sended.

Fellow peddelers,

Two ways to dissipate the impact of an impact is by
expanding the area of the impact, which is what the hard
shell of a helmet does, and by expanding the duration of
time of the impact which is what the foam does. While this
is an oversimplified explanation, it is the basic physics on
which good helmet design is based. But, on my 'bent, I don't
wear one.....

it's not very far to the ground and I go very slow....

JD

 

[Just Zis Guy]

"Mikael Seierup" <[email protected]> wrote in message
news:[email protected]...

> http://www.bhsi.org/henderso.htm 4.5 and 4.6

And you believe what BHSI say? I asked them why they are
still quoting the original Thompson, Rivara and Thompson
figures despite their having been revised (substantially
downwards) in 1996. This is their reply:

"We are aware of the second study, but by the time it
appeared the 85% figure was so deeply ingrained in the
injury prevention community that a change will not be
helpful. I regard any similar numbers published in those
or other studies as approximations anyway. Over the years
observation of who gets head-injured and who does not
seems to support the 85% number. So we have left it up
that way. We do have references to the later study for
those who need more."

In other words, don't confuse people with the facts, we'll
lead with the biggest made-up number we can find and if
folks can be bothered to dig around the site they might
discover it's ********.

Oh, and the "observation" appears to be in the form of meta-
analyses, all based on the same small group of original
studies. No country has ever approached even within an order
of magnitude the kinds of injury savings TR&T predict.

Oh, and "88%" and "85%" in the original studies are, within
the confidence limits used by the authors, actually
"somewhere between 60% and 100%" - a very wide margin of
error which is inconsistent with the degree of precision of
the figure quoted (the engineer in me speaking).

--
Guy
===
May contain traces of irony. Contents liable to settle after
posting. http://www.chapmancentral.co.uk

88% of helmet statistics are made up, 65% of them at
Washington University

 

[Harv]

"Jack Davis" <[email protected]> wrote in message
news:[email protected]...
>
> "Patrick Herring" <[email protected]> wrote in message
> news:[email protected]...
> > "Mikael Seierup" <[email protected]> wrote:
> >
> > |
> > | "Cletus D. Lee" skrev...
> > |
> > | Dave Kahn blurted...
> >
> > Actually that was me blurting...
> >
> > | > > No it isn't.
> > |
> > | http://www.bhsi.org/henderso.htm 4.5 and 4.6
> >
> > You may be confusing "It is the liner of the helmet that
> > is responsible for absorbing the energy of impact
> > through its own destruction." with the whole helmet
> > being broken. "destruction" here means "being crushed to
> > absorb energy that would otherwise deform your skull",
> > and the outer shell keeps the inner foam in place in
> > order that it does that, which it won't if it breaks.
> >
> > However, there are helmets with no outer shell. To me
> > that just emphasises how little protection bike helmets
> > are intended to give.
> >
> > | Oh, yes it is. You just ride without one though. Ride
> > | like the wind, Sonnyboy, and take lots of chances.
> >
> > I don't ride like the wind & I take as few chances as
> > I can.
> >
> > | Oh wait, maybe you already did. Yea, that sure
> > | explains a lot. ;o)
> >
> > <twitch><twitch>
> >
> > --
> > Patrick Herring, Sheffield, UK http://www.anweald.co.uk
> >
> > Eala Earendel engla beorhtast ofer middangeard monnum
> > sended.
>
> Fellow peddelers,
>
> Two ways to dissipate the impact of an impact is by
> expanding the area of the impact, which is what the hard
> shell of a helmet does, and by
expanding
> the duration of time of the impact which is what the foam
> does. While
this
> is an oversimplified explanation, it is the basic physics
> on which good helmet design is based. But, on my 'bent, I
> don't wear one.....
>
> it's not very far to the ground and I go very slow....
>
> JD

Quite right Jack. If the forces on the foam are too low
(load per unit area) to cause deformation, then the impact
is not dissipated. The deformation of the cushion is not to
keep the skull from deforming, but to decellerate the brain
mass so it doesn't impact against the skull. It is this
impact that can cause large trauma.

 

[Harv]

"Just zis Guy, you know?" <[email protected]> wrote in message
news:[email protected]...
> "Tom Sherman" <[email protected]> wrote in message news:[email protected]
> berlin.de...
> > Zust zis Guy, you know? wrote:
>
> > Without examining the failure surface one can only
> > speculate as to the cause of the failure, but the most
> > probable is fatigue.
>
> It is a classic fatigue failure, looking at it, as the
> last one was. Whether this would have been mitigated by
> better heat treatment I couldn't say.
>
> --
> Guy
> ===
> May contain traces of irony. Contents liable to settle
> after posting. http://www.chapmancentral.co.uk
>
>

A recent article and discussion in Machine Design Magazine
about welded aluminum and heat treatment indicate that
proper design can mitigate the need for heat treatment.
Weldments such as ships' superstructures were mentioned as
examples of things impractical to heat treat, but that
musn't fail in service.

 

[Chris Malcolm]

"Jack Davis" <[email protected]> writes:

>Two ways to dissipate the impact of an impact is by
>expanding the area of the impact, which is what the hard
>shell of a helmet does, and by expanding the duration of
>time of the impact which is what the foam does. While this
>is an oversimplified explanation, it is the basic physics
>on which good helmet design is based. But, on my 'bent, I
>don't wear one.....

>it's not very far to the ground and I go very slow....

And presumably you travel feet first and head last?

--
Chris Malcolm [email protected] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]

 

[Just Zis Guy]

On Mon, 08 Mar 2004 19:57:51 -0600, Tom Sherman
<[email protected]> wrote in message
<[email protected]>:

>Does the Optima Stinger have the same gussets in this area
>that the second generation Baron has (after numerous
>failures at this point on the first generation)?

Revised answer: up to a point. They have upgraded the
aluminium and the heat treatment, and added a gusset plate,
but no fillet as per the Baron. They've also increased the
steering tube diameter to increase the size of the weld (not
sure why that would help) and removed some drillings and
routed cables outside the frame, which is less neat but
removes some stress points.

Hmmmm.

--
Guy
===
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk

88% of helmet statistics are made up, 65% of them at Washington University