1、Designation: F3211 17Standard Guide forFatigue-to-Fracture (FtF) Methodology for CardiovascularMedical Devices1This standard is issued under the fixed designation F3211; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast 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 guide is intended to provide an experimentalmethodology to assess and determine the structural fatigue lifeof impl
3、antable cardiovascular medical devices.1.2 This guide is also intended to provide methodologies todetermine statistical bounds on fatigue life at in vivo useconditions using measured fatigue life derived in whole or inpart from hyper-physiological testing to fracture.1.3 This guide may be used to as
4、sess or characterize devicedurability during design development and for testing to deviceproduct specifications.1.4 Fretting, wear, creep-fatigue, and absorbable materialsare outside the scope of this guide, though elements of thisguide may be applicable.1.5 As a guide, this document provides direct
5、ion but doesnot recommend a specific course of action. It is intended toincrease the awareness of information and approaches. Thisguide is not a test method. This guide does not establish astandard practice to follow in all cases.1.6 This guide is meant as a complement to other regulatoryand device-
6、specific guidance documents or standards and itdoes not supersede the recommendations or requirements ofsuch documents.1.7 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-pri
7、ate safety, health and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.8 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopm
8、ent of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E178 Practice for Dealing With Outlying ObservationsE456 Terminology Relating to Quality and StatisticsE468 Practic
9、e for Presentation of Constant Amplitude Fa-tigue Test Results for Metallic MaterialsE739 Practice for StatisticalAnalysis of Linear or LinearizedStress-Life (S-N) and Strain-Life (-N) Fatigue DataE1823 Terminology Relating to Fatigue and Fracture TestingF2477 Test Methods forin vitro Pulsatile Dura
10、bility Testingof Vascular StentsF2942 Guide forin vitro Axial, Bending, and TorsionalDurability Testing of Vascular StentsF3172 Guide for Design Verification Device Size andSample Size Selection for Endovascular Devices2.2 ISO Standards:3ISO 5840-x Cardiovascular implants - Cardiac valve pros-theses
11、 - Part 1: General requirements, Part 2: Surgicallyimplanted heart valve substitutes, Part 3: Heart valvesubstitutes implanted by transcatheter techniquesISO 12107 Metallic materials - Fatigue testing - Statisticalplanning and analysis of dataISO 25539-x Cardiovascular implants - Endovascular de-vic
12、es - Part 1: Endovascular prostheses, Part 2: Vascularstents, Part 3: Vena cava filters2.3 Regulatory Guidance:Guidance for Industry: Q9 Quality Risk Management, FDA,200643. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 acceptance criteriaspecific numerical limits orranges or o
13、ther conditions identified prior to testing that1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devices and is the direct responsibility of SubcommitteeF04.30 on Cardiovascular Standards.Current edition approved Sept. 1, 2017. Published Septembe
14、r 2017. DOI:10.1520/F3211-17.2For 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.3Available from International Or
15、ganization of Standards, http:/www.ISO.org/ISO/store.htm4Accessed June 23, 2016 (http:/www.fda.gov/downloads/Drugs/./Guidances/ucm073511.pdf).Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in
16、accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1establish the required resu
17、lts to support a conclusion, adecision, or meet a specification.3.1.2 amplitudeone-half of the difference between themaximum and minimum measurements of the cyclic wave-form.3.1.3 censordata where the cycle count at failure is onlypartially known. Run-outs (see definition in 3.1.26) are a formof rig
18、ht-censored data. Tests that use periodic inspections todetermine the cycles to fracture are interval censored as thecycle of fracture is unknown but bounded between the previousand current inspection cycle counts.3.1.4 componenta test specimen comprised of a subas-sembly or an individual part of a
19、cardiovascular medical devicein its finished form.3.1.5 confidence levelthe probability that the true valuefor a parameter of interest will fall within a numerical interval.The interval is known as the Confidence Interval. ConfidenceIntervals are used to establish boundaries for the value of aparame
20、ter of interest.NOTE 1Confidence levels, typically stated as percentages, are typi-cally chosen through a risk analysis.3.1.6 coupona test specimen extracted from a cardiovas-cular medical device or a component in its finished form.3.1.6.1 DiscussionOften a coupon is “clipped” or cut froman as-manuf
21、actured device.3.1.7 design curvethe lower confidence bound for a reli-ability quantile of the fatigue life distribution. For example, theLoad versus fatigue life Number of cycles (S-N) curve for p%survival at c% confidence. See Fig. 1.3.1.8 design lifethe number of cycles for which the deviceis des
22、igned to remain functional without significant perfor-mance degradation.3.1.9 devicea complete cardiovascular medical implant inits final form, or as deployed, that may be used as a testspecimen.3.1.10 duty cyclea time history of loading conditions.EXAMPLEFor devices deployed into the vasculature of
23、 thelower limbs, a duty cycle may be defined by the number ofsteps per day, the number of stairs per day, and the number ofsit/stand cycles per day.3.1.11 failurepermanent deformation or fracture withcomplete separation that renders the device ineffective orunable to adequately resist load. Other cr
24、iteria may be used butshould be clearly defined.3.1.12 failure modea combination of an external loadtype, a fracture location or locations, and a fracture type. Theexternal load can be single modes such as bending or twistingtorques, radial loads, tension-compression axial loads, and soforth, or com
25、binations of such loads. Fracture locations arepositions on a device at which fracture occurred such as in astent connector, stent apex, or stent strut. The fracture type ischaracterized by the surface morphology and the materialcause or causes of the fracture such as tensile overload,transverse she
26、ar, mixed-mode, high cycle fatigue, or low cyclefatigue.3.1.13 fatigue factor of safetythe ratio of the FatigueStrength at a Specified Life with prescribed reliability andconfidence levels to the load at the specified use condition. TheFatigue Factor of Safety is specific to a single failure mode.FI
27、G. 1 Fatigue Life Model Depicting Terminology Where S is Load Parameter and N is Fatigue Life, Number of Cycles to FractureF3211 1723.1.13.1 DiscussionWhen mean loads are consideredalong with the alternating loads, the ratio calculation must bedefined and preferably shown on a constant life fatigued
28、iagram.3.1.13.2 DiscussionIn communicating a Fatigue Factor ofSafety, a clear statement of its intended purpose and theassumptions associated with its calculation is necessary forproper interpretation. For example, a safety factor estimatebased on the average amplitude at fracture at the design life
29、relative to the amplitude at the typical use condition will besubstantially different from a safety factor based on the 90 %reliability/95 % confidence amplitude at fracture at the designlife relative to a conservative estimate of the most challenginguse condition amplitude.3.1.14 fatigue life model
30、a mathematical equation thatdescribes the relationship between fatigue life and loadingparameters with prescribed reliability and confidence, statisti-cally derived from experimental fatigue data. See Section 7.2 .3.1.15 fatigue strength at a specified lifethe maximumload the test specimen can be ex
31、pected to survive for aspecified number of cycles with a stated confidence andreliability.3.1.15.1 DiscussionThe Design Curve at a specified lifemay be used to show this graphically. See Fig. 1.3.1.15.2 DiscussionThe Fatigue Strength is specific to asingle failure mode. See Terminology E1823.3.1.16
32、fracturecomplete separation of any device compo-nent due to stress with exposure of new surfaces that werepreviously together.NOTE 2A fracture does not necessarily represent a device functionalfailure.3.1.17 FtFacronym for Fatigue-to-Fracture.3.1.18 hyper-physiological test conditionstest loads that
33、exceed the expected in vivo use conditions.3.1.19 loadused to denote continuous and time-varyingforces, stresses, strains, torques, deflections, twists or otherparameters that describe the applied fatigue stimuli. Typicallythese fatigue stimuli are described by a mean value and analternating value.N
34、OTE 3Units and symbols are dependent on the parameter of interest.3.1.20 physiological loadsloads expected on the deviceduring in vivo use.3.1.21 preconditioningsimulated use preparation of thespecimen prior to testing. See Section 6.12.3.1.22 protocola set of instructions that typically definesthe
35、specimens, test procedures, analysis procedures, and ac-ceptance criteria.3.1.23 quantilevalue such that a fraction of the sample orpopulation is less than or equal to that value. See TerminologyE456.3.1.24 reliabilitythe probability of survival to the speci-fied design life at a given loading condi
36、tion.3.1.24.1 DiscussionFor the purpose of this standard, thisis a narrow statistical measure of reliability of the device basedon in vitro data and modeling. In general, higher reliability inFtF is expected to increase the clinical reliability.3.1.25 risk analysis(1) a methodical analytical approac
37、hto determine and address identified system or componentfailure modes and their associated causes, based on theprobability of occurrence and the severity of their effects onsystem performance and patient safety; (2) an estimate of therisk associated with identified hazards in accordance with FDAQ9 Q
38、uality Risk Management.3.1.26 run-outno fatigue failure at a specified number ofload cycles. See Terminology E1823. This number is typicallyspecified prior to beginning the testing.3.1.27 sample sizethe quantity of individual specimenstested. The sample size is typically chosen to establish confor-m
39、ance to a pre-determined specification with appropriatestatistical confidence levels.3.1.28 load versus life (S-N) curvegraphical representa-tion of fatigue life data (see Fig. 1). The curve indicates theload versus cycles-to-fracture relationship for a specifiedprobability of survival, for example,
40、 the 50th,90th,or95thpercentile.NOTE 4For N, a log scale is commonly used. For loads in stress orstrain, either a logarithmic or a linear scale is commonly used. SeeTerminology E1823. For the purpose of analysis, the S-N curve iscommonly modeled using a load-life relationship, for example a PowerLaw
41、 or Coffin-Manson equation.3.1.29 strength distribution at life Nthe probability offracture at the life N as a function of load. The distribution maybe computed by integrating the fatigue life distribution at eachload from 0 to N.3.1.30 surrogatea test specimen constructed to represent adevice, comp
42、onent, or region of interest of a cardiovascularmedical device in its finished form.3.1.31 test artifactspurious test results attributable toconditions that are not present during in vivo use conditions(failure at the grips, for example).3.1.32 test specimena test article that is subjected tofatigue
43、 loading conditions. A test specimen (also referred to asspecimen) may be classified as a device, component, coupon,or surrogate.3.1.33 test-to-successa paradigm for assessing or charac-terizing the fatigue durability of medical devices wherebyspecimens are tested at a chosen factor of safety at or
44、nearsimulated cyclic physiological loads where no fractures areexpected. For example, the device “passes” and the test issuccessful if no devices fail by structural fracture or if alldevices maintain sufficient functional integrity. See Test Meth-ods F2477.3.1.34 use conditionsthe conditions to whic
45、h the devicewill be subject, including the cumulative effects of the finalmanufacturing state, the process of device delivery anddeployment, and the in vivo operating environment. See 6.1and 6.12.4. Summary of Guide4.1 The fatigue-to-fracture (FtF) paradigm provides a meth-odology whereby whole devi
46、ces, device components, couponsF3211 173or surrogates are tested to fracture with hyperphysiologicalcyclic mechanical loads such as deflections, forces, or torques.In many or all of the tests, the cyclic load should be sufficientto fracture the device in fewer cycles than the desired clinicallife. T
47、he resulting fatigue data are used to make a statisticalestimate of fatigue life and/or generate outputs such as afatigue safety factor and a fatigue strength distribution at thedesign life.4.2 This document provides guidance for test considerationsand choices such as determining physiologically rel
48、evant testmodes, determining load levels, selecting test specimens,defining failure, characterizing and verifying test operation,selecting the test environment, determining an appropriatesample size, setting the test frequency, setting the test duration,preconditioning test specimens, monitoring the
49、 test, inspectingfor fractures, and documenting test results.4.3 Prospective test planning procedures are illustrated togenerate a credible estimate of durability relative to the in vivouse conditions. The planning procedure can be used to generatea test protocol that includes a prospectively chosen statisticalmodel, sample size and test load levels, and rationale for thechoices.4.4 This document provides guidance on statistical interpre-tation and presentation such as selecting the fatigue life model,calculating confidence bounds
