ASTM F1880-2009 Standard Test Method for the Determination of Percent of Let-Off for Archery Bows《测定射箭弓射出百分比的标准试验方法》.pdf

1、Designation: F1880 09An 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, in the case of rev

2、ision, 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-off for archery bow

3、s.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 to use.2. Referenced

4、 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, while at the bows

5、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 perpendicular to the string

6、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 elements, or a combin

7、ation 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 draw weight.3.2.4 d

8、raw, 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 the draw cycleof a b

9、ow.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, nthe position in

10、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 the range of draw

11、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 cycle of the compou

12、nd 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 to restrain the bo

13、w 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 length by the amou

14、nt 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 SportsEquipment and Faci

15、lities and is the direct responsibility of Subcommittee F08.16 onArchery Products.Current edition approved Nov. 1, 2009. Published December 2009. Originallyapproved in 1998. Last previous edition approved in 2004 as F1880 98 (2004).DOI: 10.1520/F1880-09.2For referenced ASTM standards, visit the ASTM

16、 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United

17、 States.been 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 tension on the bowstring,normally at

18、 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 them to assume a prestressedflex

19、ed 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 peak or maximum draw force, nthe

20、maximumforce required to retain the bowstring of the drawn bow at aspecific draw length under a condition of constant tension onthe bowstring. No relaxation of the drawing force is permittedwhen measuring this force, since this introduces static hyster-esis. The peak or maximum force for compound bo

21、ws 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 abow and the lowest level of dr

22、aw 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 conditions, between the drawforce and

23、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 expressed in foot-pounds or joules.3.2.1

24、9 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 archery bows cause variation inthe

25、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 and the maximum draw weightobta

26、inable (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 uses the peak draw force and the m

27、inimum 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 methods and distinguishes between them

28、.5. Determination of the ATA Percent of Let-Off5.1 Use of the Force-Draw CurveThe values of peakforce and let-off force used to calculate the ATA percent oflet-off shall be taken from the force-draw curve. The peak forceis the maximum force obtained during the draw cycle. Thelet-off force is the low

29、 force read at the rated draw length. In allcases, the let-down force shall be read within 2 s undercontinual pull conditions, without relaxation to reach the drawlength specified. This technique eliminated the hysteresiseffect, which can distort the reading. Refer to Test MethodF1832 for the method

30、 to be used in determining the force-drawcurve.5.2 Method of CalculationThe percent of let-off shall becalculated using the following formula:percent let2off 5 100 3peak force let2off force! / peak force(1)5.3 HysteresisThe reduction due to hysteresis shall not beconsidered in the determination of t

31、he 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 thatspecific draw length.6. Effective P

32、ercent 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 of let-off, however, the exact effect i

33、s 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 reason, it can influence let-off, but i

34、ts 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 092ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item ment

35、ionedin 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 any time by the responsible technical committee

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38、ox C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).F1880 093