ASTM F1880-2009(2013) Standard Test Method for the Determination of Percent of Let-Off for Archery Bows《测定拱形弓发射力的百分比标准试验方法》.pdf

1、Designation: F1880 09 (Reapproved 2013) An American National StandardStandard Test Method for theDetermination of Percent of Let-Off for Archery Bows1This standard is issued under the fixed designation F1880; the number immediately following the designation indicates the year oforiginal adoption or,

2、 in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the procedure to be used todetermine the percent of let-

3、off for archery bows.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior t

4、o use.2. Referenced Documents2.1 ASTM Standards:2F1832 Test Method for Determining the Force-Draw andLet-Down Curves for Archery Bows3. Terminology3.1 Acronyms:3.1.1 ATAArchery Trade Association3.2 Definitions:3.2.1 ATA actual draw length, ndistance from the bowsstring at the nocking point location,

5、 while at the bows fulldraw condition, measured perpendicular to a vertical linethrough the pivot point of the bow grip, plus 134 in. (+14 ,0 in.).3.2.2 brace height, nthe distance in inches or millimetresfrom the shooting string of a bow to the pivot or low point ofthe hand grip, measured perpendic

6、ular to the string at theun-drawn condition.3.2.3 compound bow, na type of bow that imposes asecondary system of control of the force-draw characteristic onthe usual limb geometry control system of the conventionalbow. This secondary control system can be composed of cams,levers, cables, or other el

7、ements, or a combination thereof. Thedual control system permits great versatility in the design of theforce-draw characteristic and simplifies the inclusion of let-off.In general, it is normal for compound bows to have greaterstored energy than conventional bows for a given level of peakor maximum

8、draw weight.3.2.4 draw, nto move the shooting string of a bow fromthe rest or brace position toward the fully drawn position byapplying force to said string. Such action causes the limbs ofthe bow to bend and store energy. Moving the string from braceheight to the full-draw position corresponds to t

9、he draw cycleof a bow.3.2.5 draw force, nthat level of force necessary andcoincidental with drawing a bow to a specific position withinits ATA actual draw length.3.2.6 force-draw curve, nthe curve obtained when thedraw force is plotted versus the ATA actual draw length for agiven bow.3.2.7 full draw

10、, nthe position in a draw cycle of a bowfrom which the string of the bow is released and the forceapplied to the rear of the arrow to commence the launch. Thefull-draw position of individual archers will vary due topersonal physical characteristics and shooting style. Archerybows are specified as to

11、 the range of draw length that they willaccommodate to permit archers to select a size that will fitthem. Precise draw length is less of a factor on conventionalbows as compared with compound bows, since it is ideal tomatch the draw length of the archer to the position ofmaximum let-off in the draw

12、cycle of the compound bow. Theposition of maximum let-off for compound bows usually isadjustable within specified limits.3.2.8 holding force, nthe force required to retain thebowstring of a drawn bow at a specificATAactual draw length.3.2.9 let-down curve, nthe curve obtained when the forcenecessary

13、 to restrain the bow from returning to brace height isplotted versus the ATA actual draw length.3.2.10 let-down force, nthe force required to retain thebowstring of the drawn bow at a specific ATA actual drawlength during the let-down cycle. This let-down force differsfrom the draw force at the same

14、 length by the amount of statichysteresis.3.2.11 let-off, nthat characteristic of an archery bow thatresults in a reduction in the force necessary to increase thedraw length of the bow after the highest level of draw force has1This test method is under the jurisdiction of ASTM Committee F08 on Sport

15、sEquipment, Playing Surfaces, and Facilities and is the direct responsibility ofSubcommittee F08.16 on Archery Products.Current edition approved Nov. 1, 2013. Published January 2014. Originallyapproved in 1998. Last previous edition approved in 2009 as F1880 09. DOI:10.1520/F1880-09R13.2For referenc

16、ed ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Con

17、shohocken, PA 19428-2959. United States1been reached. This is a characteristic generally associated with,but not restricted to, compound type bows.3.2.12 let-off force, nthe minimum force required to retainthe bowstring of the drawn bow subsequent to peak draw forceunder a condition of constant tens

18、ion on the bowstring,normally at full draw.3.2.13 non-compound bow, na bow constructed in theconventional manner, having two flexing limbs extendingoutwardly in opposite directions from a handle. A singleshooting string of a length shorter than the bow, connects theextreme ends of the limbs causing

19、them to assume a prestressedflexed condition. Drawing the bow causes additional bendingand stressing of the limbs, storing the energy necessary topropel the arrow. Control of the force-draw characteristic of thebow is exercised entirely by the static and dynamic geometryof the flexing limbs.3.2.14 p

20、eak or maximum draw force, nthe maximum forcerequired to retain the bowstring of the drawn bow at a specificdraw length under a condition of constant tension on thebowstring. No relaxation of the drawing force is permittedwhen measuring this force, since this introduces static hyster-esis. The peak

21、or maximum force for compound bows usuallyoccurs about half way through the draw cycle, while onconventional bows it normally occurs at the end of the drawcycle since there is no let-off.3.2.15 percent of let-off, nthe difference between the peakor maximum draw force reached during the draw cycle of

22、 abow and the lowest level of draw force reached subsequent tothat peak, expressed as a percentage of the peak force.3.2.16 power-stroke, nthe distance in inches or millime-tres from brace height to full draw.3.2.17 static hysteresis, nthe difference in pounds ornewtons, measured under static condit

23、ions, between the drawforce and the let-down force for any given draw length.Integrated over the full power stroke of the bow, the statichysteresis is expressed as foot-pounds or joules of energy.3.2.18 stored energy, nthe energy required to draw a bowfrom brace height to full draw, usually expresse

24、d in foot-pounds or joules.3.2.19 zero intercept, nthe point of zero intercept isdefined as the brace height plus 134 in. (44.5 mm). It is the zeroforce position on the force-draw curve.4. Significance and Use4.1 It is recognized that certain designs of the cams used inthe compounding systems of arc

25、hery bows cause variation inthe percent of let-off with change in draw length, draw weight,or both. This is true particularly with the style of cam thatachieves draw length adjustment by effectively altering thelength of the shooting string by any of several methods. In thiscase, the mid-draw length

26、 and the maximum draw weightobtainable (but not to exceed the maximum rated weight of thebow) shall be used to determine the official percent of let-offfor the bow in question.4.2 Historically, two methods have been in use to establishthe percent of let-off for archery bows. The most commonmethod us

27、es the peak draw force and the minimum holdingforce read from the force-draw curve to calculate the percent oflet-off. The second method uses the peak draw force from theforce-draw curve and the minimum holding force from thelet-down curve for this calculation. This test method definesthe two method

28、s and distinguishes between them.5. Determination of the ATA Percent of Let-Off5.1 Use of the Force-Draw CurveThe values of peak forceand let-off force used to calculate the ATA percent of let-offshall be taken from the force-draw curve. The peak force is themaximum force obtained during the draw cy

29、cle. The let-offforce is the low force read at the rated draw length. In all cases,the let-down force shall be read within 2 s under continual pullconditions, without relaxation to reach the draw length speci-fied. This technique eliminated the hysteresis effect, which candistort the reading. Refer

30、to Test Method F1832 for the methodto be used in determining the force-draw curve.5.2 Method of CalculationThe percent of let-off shall becalculated using the following formula:percent let 2 off 5 100 3 peak force let 2 off force!/peak force (1)5.3 HysteresisThe reduction due to hysteresis shall not

31、 beconsidered in the determination of the force value at eitherpeak or let-off condition when determining the ATA percent oflet-off.5.4 Rating ConditionsThe bow shall be rated for percentof let-off with the draw length set in mid-range and the peakdraw weight adjusted to the maximum rated value for

32、thatspecific draw length.6. Effective Percent of Let-Off6.1 Hysteresis EffectThe difference in force at the fulldraw condition between the draw and let-down curves isnormally in the range of 6 to 10 % of the peak draw force.Under certain conditions, this hysteresis can increase theeffective percent

33、of let-off, however, the exact effect is depen-dent on the specific bow design. The hysteresis becomes afactor when the bow is drawn past full draw and let down orrelaxed to the anchor position. It is not a factor when thebowstring is drawn to the anchor position without incipientlet-down. For this

34、reason, it can influence let-off, but its effectis dependent upon the technique used to bring the bowstring tothe anchor position.7. Keywords7.1 brace height; draw length; force-draw curve; full-draw;let-offF1880 09 (2013)2ASTM International takes no position respecting the validity of any patent ri

35、ghts asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at an

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37、ill receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by A

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