General question about metal strength

Robert Connolly robert at linuxfromscratch.org
Sun Feb 26 11:27:18 PST 2006


On February 24, 2006 02:28 pm, Archaic wrote:
> On Thu, Feb 23, 2006 at 10:59:38PM -0500, Robert Connolly wrote:
> > I feel more confident with a single piece toe cap, than one with multiple
> > layers of shapes, assuming both are the same material and mass. A multi
> > layer cap is only as strong as the strongest layer, the rest will
> > collapse.
>
> But the absorbsion rate of the collapsing layers proves infinitely
> useful. That's why many car panels are made to fly off. If you can get
> the load of a moving object closer to it's static load, then the
> strength of the final layer needn't be so high allowing for lighter and
> more comfortable boots.

I have read a bit about modern tank armor. They sometimes use perforated 
material, and spaced armor. Perforated steel is usually the core of the 
armor, sandwiched between solid plates. It allows the core armor to be 50% 
lighter while only losing 30% of the strength, unless it is curved because 
then it gets weaker and the weight to strength ratio starts to balance. 
Spaced armor is more effective against chemical attacks than kinetic attacks, 
so it is not so usefull to me.

----------		<-- Thin solid layer
| | | | | |		<-- Perforated layer
_______		<-- Thick bottom layer

I think it is better, in my situation, if the perforated layer is much softer 
than the top and bottom, allowing it to squish. Such as aluminum sandwiched 
between steel, or even soft-wood sandwiched between steel.

A honeycomb would be a variation of perforation. I'm not sure which is better.

> Likewise a rounded top will not distribute the 
> weight down it's sides as effectively as a pointed (triagular) top since
> the load would have to spread across the top of the toe before moving
> down the sides. That spreading means much of the pressure is unloaded
> before it takes a downward turn. However, the smaller point of impact of
> a pointed top would result in a higher PSI for an instant and sufficient
> reinforcement would be required.

Armored glass is always curved/bubbled. Flat glass won't absorb or deflect 
bullets, or kinetic energy, as well as bubbled glass. Some tanks have few 
curved surfaces, but I think this is because they use ceramic in the core of 
the armor, and ceramic can't be bent/curved. Some tanks have a lot of curves.

As for toe caps, some impacts are not directly on the top of the cap, they can 
be towards one side or the other. An octagonal prism, or pyramid, is 
strongest at the corners, and weakest at the flat panels. A dome has no 
strongest or weakest region, and would be more effective when you can't be 
sure where the impact will be... if a box is falling straight down but the 
box itself is on a 45 degree axis, a dome will absorb it better than a 
pyramid. But the dome is more vulnerable to a directly downward impact.

Maybe there's a way to balance the two with a multi-layer cap.

robert

> * = the direction of travel of the pressure.
>
>          *              *
>          *              *
>     * * * * * *       *   *
>    *  -------  *     * /-\ *
>    * |       | *    * /   \ *
>    * |       | *   * /     \ *
>
>
> --
> Archaic
>
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