ASTM_E_1544_-_99_2004e1.pdf

Designation:E 1544 99(Reapproved 2004)e1Standard Practice forConstruction of a Stepped Block and Its Use to EstimateErrors Produced by Speed-of-Sound Measurement Systemsfor Use on Solids1This standard is issued under the fixed designation E 1544;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.e1NOTEThe correct Figure 2 was reinstated in May 2004.1.Scope1.1 This practice provides a means for evaluating bothsystematic and random errors for ultrasonic speed-of-soundmeasurement systems which are used for evaluating materialcharacteristics associated with residual stress and which mayalso be used for nondestructive measurements of the dynamicelastic moduli of materials.Important features and constructiondetails of a reference block crucial to these error evaluationsare described.This practice can be used whenever the precisionand bias of sound speed values are in question.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 Documents2.1 ASTM Standards:2E 650 Guide for Mounting Piezoelectric Acoustic EmissionSensorsE 494 Practice for Measuring Ultrasonic Velocity in Mate-rials3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 path lengthlength of track along which the soundwaves actually propagate.3.1.2 time of flightthe measured time interval between thelaunching of a sonic input pulse at the start of a path and thetime of reception of the pulse at the end of the path of travel.3.1.2.1 DiscussionThere are many different techniquesused to avoid termination errors related to electronic delays andtermination impedance effects and end interference.One com-monly accepted procedure is to make the time measurementbetween successive echoes instead of using the electricaldriving pulse as the start marker.Reference techniques that usetwo nearly identical sets of experiments,where one is thereference and the other the unknown and in which thedifference in time of travel is the output result,cancel out manyof the errors mentioned above(1).34.Summary of Practice4.1 The physical quantity,speed of sound of a particularsolid,is not a fundamental constant because it depends onseparate measurements of time and distance.It is a computedvalue derived from measured values of distance and of timeand is based on assumptions about the elastic material throughwhich the sound waves travel.Because this quantity is not afundamental property(dependent upon many other variablesbesides time and distance)of any material,a reference standardhaving a specific value of speed of sound is virtually impos-sible to construct.Thus,questions of accuracy have to beaddressed in a different way.4.2 The measurement of sound speed depends upon manyfactors.Considerations of the uniformity of both the elastic andthe density characteristics of the material,of internal scattering,of transducer coupling and loading,of temperature uniformityand value,of external pressure and stress,and of many otherphysical effects that would alter the overall measurementprocess must be taken into account.Because the speed ofsound is affected by so many physical parameters,the onlyavailable test to evaluate the detrimental influence of thesehigher order variables is to examine their combined effects onmeasured speed of sound values as it relates to the definition:V 5 L/t(1)1This practice is under the jurisdiction ofASTM Committee E-28 on MechanicalTesting and is the direct responsibility of Subcommittee E28.13 on Residual StressMeasurement.Current edition approved April 1,2004.Published MAy 2004.Originallyapproved in 1993.Last previous edition approved in 99 as E 1544 99.2For referenced 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.3The boldface numbers in parentheses refer to a list of references at the end ofthe text.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.4.2.1 This defining equation for the sound speed,V,states aconstant relationship between path length,L,and time of flight,t,and is applicable primarily to methods in which the time ismeasured directly(2).4.3 Several different methods of measuring speed of soundexist.A number of these are itemized in Practice E 494.(McSkimin details many ingenious methods in Ref(1).Regardless of the method used to calculate the sound speedfrom two measurements,the intent is to determine this con-stant,V,that