Re: Speed and the fear of falling off

For all discussions about this "lively" subject. All topics that are substantially about helmet usage will be moved here.
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Graham
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Re: Speed and the fear of falling off

Postby Graham » 7 Jun 2020, 8:02pm

This is possibly the most concise summary of the "debate" :-

Fortunately, we still have the freedom to choose whether to wear one or not.

https://www.bmj.com/content/346/bmj.f38 ... eytype=ref

You are free to disagree.

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[XAP]Bob
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Re: Speed and the fear of falling off

Postby [XAP]Bob » 8 Jun 2020, 12:39pm

al_yrpal wrote:
[XAP]Bob wrote:
al_yrpal wrote:Rather a cracked helmet than a cracked skull. Thats how helmets work they absorb impact but like climate change deniers a tiny minority disagree. Take no notice....

Al



Helmets absorb energy by crushing, not by cracking.
If a helmet cracks then that shows very little, if it has crushed (even if it has cracked as well, the outer shell can hold it together) then that is the indication that it has absorbed energy.

Whether that energy absorption is useful or not is a ghetto discussion.
Whether that energy absorption is less likely to have been needed without the aforementioned garment is also a ghetto discussion.


Sorry that is incorrect. Have a read up on tne Izod test. I studied Mechanics and Strength of materials for 5 years and you are talking absolute... deformation absorbs energy and cracking or fracturing occurs when the impact is beyond the materials ability to deform. If you want all the energy to go into deforming or cracking your skull the answer is simple, dont wear a helmet.

Al


Quote from the source of all well repeated lies:
Impact tests are used in studying the toughness of material. A material's toughness is a factor of its ability to absorb energy during plastic deformation. Brittle materials have low toughness as a result of the small amount of plastic deformation they can endure.


i.e. brittle fracture absorbs very little energy, plastic deformation (i.e. crushing) absorbs potentially useful amounts.

Which is exactly what I said - the fact that a helmet has cracked only shows brittle fracture, and very little energy absorption. If it has crushed (irrespective of whether it has cracked or not) then *that* shows potentially useful energy absorption.

All of that is irrelevant if the collision is less likely without a magic hat - because that change in risk makes at least as much difference as the magic hat might, if it is hit in the right way.

Find me a helmet where the manufacturer makes safety claims rather than style claims.
One of the biggest problems is figuring out which tests have been done on a particular design of hat, and then realising that none of the relevant tests include any rotational element, which is generally regarded as the most damaging acceleration mode for the grey matter.
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.