BSISO14242-2:2016 IS014242-2:2016(E) 4.4.7Repeat 4.4.2to4.4.6at intervalsuntil the incremental mass changeofthe specimen over24h is lessthan10%ofthepreviouscumulativemasschange. 4.4.8 Record theaverageincreaseinmass S ofthecontrol specimen. 4.5J Procedureforgravimetricmeasurement 4.5.1 Mount thetestpieces in thetesting machine and conduct the weartest in accordance with ISO14242-1orIS14242-3asappropriate. 4.5.2 Recordthemass ofthespecimens. 4.5.3 Oneachoccasionwhenthetest specimenandcontrol specimenareremoved fromthewear- testing machine, repeat the procedures 4.4.2 to 4.4.6, 4.5.1 and 4.5.2. 4.5.4 Calculatethegravimetric wearas shown inFormula (1) Wn = Wan + Sn (1) where Wn is the net mass loss after n cycles ofloading: Wan is theaverageuncorrectedmassloss Sn is the average increase inmass ofthe control specimen over the same period. 4.5.5 Calculate the average wear rate aG using Formula (2) for the least squares linear fit relationship between Wn andthe numberof loadingcycles n: Wn= aG×n + b (2) whereWnisthenetlossinmassafterncyclesandbisa constant. The zero time point shall not be used in this calculation. 5Dimensional change method 5.1Principle Acoordinatemeasuring machineisusedto mapthearticulating surface ofatotal hipprosthesisrelative toa referenceposition,direction and planepriortothe startof theweartest and at suitable intervals duringthetest.Fromthese data,thevolumetricchangebetween measurements isdetermined.Loaded non-articulating controls are intended to allow the effects of plastic flow, mainly occurring in the first 5×105 cycles,tobe separated frommaterial loss. 5.2 Apparatus 5.2.1 Three-dimensional coordinate measuring machine, with maximum axial-position error of measurementD,inmicrometres,of: D = 4 + 4l × 10-6 (3) wherelisthenumericalvalueofthedimension,expressed inmetres @ IS0 2016-All rights reserved 3 BSISO14242-2:2016 IS014242-2:2016(E) 5.2.2 Ultrasonic cleaner. 5.3Procedurefordimensionalchangemeasurement 5.3.1 Select apoint of reference, an origin and a plane on the test specimen.Maintain this reference systemthroughoutthe procedure. 5.3.2 Cleanthespecimens. 5.3.3 To ensure dimensional stability,retain the test specimen at themeasurementtemperature±2C (measured at thenormalpoints ofthemetrologylaboratory)foratleast48h. 5.3.4Atthe beginning ofa series oftests, check thatrelocation ofthetest specimen does not affect the measuredvolumebymorethan0,05%. Thismaybe achieved bytheuseoffixturing or therecognition offeatures in software,for example. 5.3.5Start the measurement machine and produce a full three-dimensional contour mesh of the articulating surfaceofthetestspecimen.Ensurethemesh spacing isnogreaterthan1mm inthe horizontalplaneoralonganyarc. 5.3.6CalculatethevolumeVnof theacetabularcavity,wherenisthenumberofwearcycleswhich havebeenapplied. 5.3.7Expressthewearas thevolume changeafter nloadingcycles,Vn,as shown in Formula (4): AVn = Vn - Vo (4) where Vois the original volume. 5.3.8Insert thetestspecimenandany control specimen in thetestingmachineandconductthetests inaccordancewithISo14242-1orIS014242-3asappropriate. 5.3.9On each occasion whenthetestspecimenand thecontrol specimenareremovedfromthetesting machine, repeat procedures 5.3.2 to 5.3.7. 5.3.10Calculatethewear rate,av,usingFormula(5)for theleastsquares linear relationshipbetween Vnandnas: △Vn=av×n+b (5) wherebisaconstant,usingaleastsquaresfit. When controls areprovided, the slope ofthe line,representing the rate of creep, should be calculated includingthezero timepoint.The zerotimepoint shall notbeused in the slopecalculationfor thewear rate ay. Test report 6 Thetestreportshallincludethefollowing information: a)areferencetothispartofISO14242,i.e.IS014242-2; b)theidentityofthetest specimens,as stated bytheparty submittingthe specimenfortest; 4 IS0 2016- All rights reserved BS ISO 14242-2:2016 IS014242-2:2016(E) the method of wearmeasurement (i.e.gravimetric or dimensional change); d) the value Wnfor each measurement using the gravimetric method,