Hysterisis Anyone?

[konrad]

I have been researching modern archery for some three years now and have yet to find a discussion on the effects of hysteresis on the efficiency of limbs on compound bows.

Whenever I am at an archery range, I am always surprised by how little time is given for the bow to recover before the next shot is fired.

From past life in the elastomer industry, I learned the effects of repeated flexing of materials (supposedly elastic) and the resulting internal heat build up dramatically changing the material’s rebound properties (hysteresis). Those tests are based counting flexural cycles to failure at a known flex cycle time and percentage of bend measured in degrees of a standard sized flat sample of material.
Failures are always related to internal heat build up.

If the material in question is given time for heat dissipation, the tested material invariably withstands many more flex cycles before less energy is required to flex and ultimate failure occurs.

I would think that modern bow limbs would exhibit the same types of heat build up and losses of efficiency (i.e. the difference between the energy required to draw the bow and the energy released during the firing sequence) during rapid shooting sessions.

Nearly all of the bow tests I have read have graphs showing draw force curves and many reports actually show the efficiency of the tested “system” (bow). Invariably, there is no data related to limb temperature.

I would like to see testing reports comparing cold limb, warm limb and hot limb efficiencies.
It seems to me this would be an excellent application for thermal imaging photography. I would guess a perfect limb design would show heat stresses evenly distributed along the entire limb length.

Some of my questions would include:
Does limb temperature affect group size?
How much arrow velocity is lost (or gained) by varying temperatures of the limb tested?
Is a quad limb system better at heat dissipation than a solid limb?
Is a “thin” limb better at heat dissipation than a standard limb?
Is a preloaded limb better at spreading stresses than a straight limb?
Does it take longer for a limb with concentrated heat stress longer to cool than one whose stress is spread more evenly?
How much time is required for any given limb to return to “cold normal”?

After all, a bowhunter most often has a cold bow in his hand and rarely has the opportunity for multiple shots.

…or am just thinking about all of this too much?

K

[quadrafire]

or am just thinking about all of this too much?

K

 
although thinking is always good. I doubt I could shoot fast enough for this to be an issue for me. I'm not accurate enough to tell anyhow. It would be good to see the result though.

[boneaddict]

   I think you are thinking too much.   

[BLKBEARKLR]

Wow, got to agree, thinking way to much.

[rasbo]

I just blow on the limbs

[whacker1]

I don't think that you could stress the limbs enough to make the kind of heat or even warming you are discussing at 70lbs draw weight.  I think it is a good question for a manufacturer, but definitely overthinking it.
Drive down to Martin archery and see if they can answer your question.

[jackelope]

Firing arrows at the rate to generate the kind of heat needed to cause this problem is something that could only be generated during the swakane late archery season by the right type of bowhunter.
 

[BULLBLASTER]

I have been researching modern archery for some three years now and have yet to find a discussion on the effects of hysteresis on the efficiency of limbs on compound bows.

Whenever I am at an archery range, I am always surprised by how little time is given for the bow to recover before the next shot is fired.

From past life in the elastomer industry, I learned the effects of repeated flexing of materials (supposedly elastic) and the resulting internal heat build up dramatically changing the material’s rebound properties (hysteresis). Those tests are based counting flexural cycles to failure at a known flex cycle time and percentage of bend measured in degrees of a standard sized flat sample of material.
Failures are always related to internal heat build up.

If the material in question is given time for heat dissipation, the tested material invariably withstands many more flex cycles before less energy is required to flex and ultimate failure occurs.

I would think that modern bow limbs would exhibit the same types of heat build up and losses of efficiency (i.e. the difference between the energy required to draw the bow and the energy released during the firing sequence) during rapid shooting sessions.

Nearly all of the bow tests I have read have graphs showing draw force curves and many reports actually show the efficiency of the tested “system” (bow). Invariably, there is no data related to limb temperature.

I would like to see testing reports comparing cold limb, warm limb and hot limb efficiencies.
It seems to me this would be an excellent application for thermal imaging photography. I would guess a perfect limb design would show heat stresses evenly distributed along the entire limb length.

Some of my questions would include:
Does limb temperature affect group size?
How much arrow velocity is lost (or gained) by varying temperatures of the limb tested?
Is a quad limb system better at heat dissipation than a solid limb?
Is a “thin” limb better at heat dissipation than a standard limb?
Is a preloaded limb better at spreading stresses than a straight limb?
Does it take longer for a limb with concentrated heat stress longer to cool than one whose stress is spread more evenly?
How much time is required for any given limb to return to “cold normal”?

After all, a bowhunter most often has a cold bow in his hand and rarely has the opportunity for multiple shots.

…or am just thinking about all of this too much?

K

i think you just gave me histersisis from reading that.

[Matt]

Extreme cold (below zero) or heat above 100 will effect your limbs.  If you leave your bow in a hot car you will not be very happy with what happens.  But just regular shooting isn't going to effect you limbs like you are thinking.  The string and cables will react to temperature way more than your limbs.  Anything above 80 degrees and depending on your string material you will see the effects.