Hello Folks, I told you I would report back when I received answers from all the manufacturers regarding my hysteresis question. Many factories had no facility for submitting an e-mail question (i.e. Mathews). Other factories did not answer at all (i.e. Bear Archery) Frankly, I was surprised by both the responses and the lack of response to what I felt was a fair question. Find below the direct quotes from the two engineering departments that did respond. My thanks go out to Martin Archery and Hoyt Archery, both of whom replied promptly. I was hoping for additional communication but was disappointed. Konrad, Thanks for the inquiry. Here is a response that I received from our engineering manager: The change in efficiency of the limbs is minor when compared to the other variables of the system. We typically run a test where we cycle (draw, let-down, repeat) a bow system for 30,000 times in a 12 hour period. This creates “significant” thermal conditions in the entire system (not just limbs). The system is then tested and the efficiencies are minimal when comparing to impact points of shot arrows. Typically the system will lose about ½% after this grueling test is run and the effects on accuracy require a shooting machine to measure at 60 yds. I know that this answer is a bit short compared to the length of your inquiry but I hope that it helps answer some of your question. Please let me know if you have further questions. Regards ~Tom Hoyt CS Team =============================================================== Hysteresis is something that can be measured, but it doesn't seem to change very much if a bow is fired at a high rate, vs. a lower rate. I personally do not believe that hysteresis accounts for a very high percentage of the wasted energy released during the shot. I think the overwhelming majority of energy loss, is due to the limbs having to move so much "stuff" that doesn't leave with the arrow. The string, cables, cams and limbs, all possess mass, that must be moved. High speed video shows how much kinetic energy remains in the bow following the shot. As archers, we feel and hear it as vibration following the shot. If we use a heavier arrow, the ratio of arrow-to-allthatotherstuff mass, is improved and the efficiency of the bow is increased. As a result, less energy is left over to make everything "bounce around" and the bow will be quieter as well. *************** There may also be other replies, but you will not receive any more notifications until you visit the forum again. All the best, Martin Tech Forum
Interesting read, do you have your original message sent to them? It's amazing how much testing these bows endure and how tough they really are. I applaud hoyt on that. I'm sure other companies do this as well.
From 4/12/2010 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 pre-loaded 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
