1、Designation: F2996 13Standard Practice forFinite Element Analysis (FEA) of Non-Modular MetallicOrthopaedic Hip Femoral Stems1This standard is issued under the fixed designation F2996; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 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 practice establishes requirements and consider-ations for the numerical simulation of non-modular (t
3、hat is,limited to monolithic stems with only a femoral head / trunniontaper interface) metallic orthopaedic hip stems using FiniteElement Analysis (FEA) techniques for the estimation ofstresses and strains. This standard is only applicable to stressesbelow the yield strength, as provided in the mate
4、rial certifica-tion.1.2 PurposeThis practice establishes requirements andconsiderations for the development of finite element models tobe used in the evaluation of non-modular metallic orthopaedichip stem designs for the purpose of prediction of the staticimplant stresses and strains. This procedure
5、 can be used forworst case assessment within a family of implant sizes toprovide efficiencies in the amount of physical testing to beconducted. Recommended procedures for performing modelchecks and verification are provided to help determine if theanalysis follows recommended guidelines. Finally, th
6、e recom-mended content of an engineering report covering the mechani-cal simulation is presented.1.3 LimitsThis practice is limited in discussion to thestatic structural analysis of non-modular metallic orthopaedichip stems (which excludes the prediction of fatigue strength).1.4 The values stated in
7、 SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 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 heal
8、th practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ISO Standards:2ISO 7206-4 (2010) Implants for SurgeryPartial and TotalHip Joint ProsthesesPart 4: Determination of EnduranceProperties and Performance of Stemmed Femoral Com-ponents3. Sign
9、ificance and Use3.1 This practice is applicable to the calculation of stressesseen on a femoral hip stem when loaded in a manner describedin ISO 7206-4 (2010). This method can be used to establish theworst case size for a particular implant. When stresses calcu-lated using this practice were compare
10、d to the stresses mea-sured from physical strain gauging techniques performed attwo laboratories using two different methods, the resultscorrelated to within 8 %.4. Geometric Data4.1 Finite element models are based on a geometric repre-sentation of the device being studied. The source of thegeometri
11、c details can be obtained from drawings, solid models,preliminary sketches, or any other source consistent withdefining the model geometry. In building the finite elementmodel, certain geometric details may be omitted from theorthopaedic implant geometry shown in the CAD model if it isdetermined tha
12、t they are not relevant to the intended analysis.Engineering judgment shall be exercised to establish the extentof model simplification and shall be justified.4.2 It is most appropriate to consider the “worst case” stresscondition for the orthopaedic implant being simulated. The“worst case” shall be
13、 determined from all relevant engineeringconsiderations, such as stem geometry, dimensions, and headoffset. If finite element analysis is being used for determiningthe worst case, then the worst case head offset may not beknown. It may be necessary to run several variants of headoffset, in order to
14、determine this.1This practice is under the jurisdiction ofASTM Committee F04 on Medical andSurgical Materials and Devices and is the direct responsibility of SubcommitteeF04.22 on Arthroplasty.Current edition approved July 15, 2013. Published August 2013. DOI: 10.1520/F2996-13.2Available from Intern
15、ational Organization for Standardization (ISO), 1, ch. dela Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http:/www.iso.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Material Properties5.1 The required material properti
16、es for input into an FEAmodel for the calculation of strains and displacement aremodulus of elasticity (E) and Poissons ratio (). These valuescan be obtained from material certification data. It should benoted that as ISO 7206-4 (2010) is run under load control, theFEA should also be run under load
17、control. When the FEA isrun under load control, the modulus of elasticity will not affectthe stress calculations under small displacement theory but willaffect displacement and strain. The influence of Poissons ratioon the stress calculations is negligible.5.2 Ensure that material property units are
18、 consistent withgeometric units in the CAD model. SI units are the preferredunits of measure.6. Loading6.1 The loading and orientation of the hip stem shall beguided by the ISO 7206-4 (2010) standard. The areas ofparticular interest are the stresses in the neck region, driverhole region, potting lev
19、el, and other design-specific criticalregions.6.2 The load shall be applied such that the magnitude anddirection are identical to that defined in ISO 7206-4 (2010).The point of load application shall produce a statically equiva-lent bending moment to a load applied through the head centerwith its wo
20、rst case head offset.6.2.1 The load in the model will be applied to the endcircular face of the hip stem trunnion or in a justifiablyequivalent manner. The trunnion may be extended or truncatedto approximate the loading conditions that simulate the worstcase head offset, which may be determined via
21、an iterativeprocess. This approximation should be reported if performed.Alternatively, a rigid couple can be used to tie the load point tothe trunnion end circular face. Refer to Fig. 1.6.2.2 It is recognized that the loading conditions in thispractice are not identical to that of ISO 7206-4 (2010).
22、However, the difference in loading conditions (for example,load applied to surface of head versus face of stem trunnion;potting level differences; use of bone cement which is notmodeled in FEA) does not significantly affect identification ofthe “worst case” stress condition and construct for subsequ
23、entbench testing, which is the primary objective of this practice.6.3 Ensure that load units are consistent with materialproperty units.7. Boundary Conditions7.1 The hip stem will first be cut at a distance from thecenter of the head as described in ISO 7206-4 (2010) with theworst case head/neck off
24、set. This cut represents the level towhich stresses and strains shall be evaluated.Asecond cut shallthen be made 10 mm below the first cut. The hip stem shall beconstrained in all directions on all faces distal to the secondcut. Constraining the stem in this manner ensures that exces-sive erroneous
25、stresses are not generated at the region ofinterest due to the influence of rigid fixation. Refer to Fig. 2,Fig. 3, and Fig. 4, which present three stem length variantsprovided in ISO 7206-4 (2010). The use of other stressevaluation levels or constraint levels, or both, shall be justified.FIG. 1 Loa
26、d ApplicationNOTE 1Generating the statically equivalent maximum bending moment by (a) an offset node tied rigidly to the circular trunnion face, or (b)acylindrical extension (or truncation of circular trunnion face which equals the maximum femoral head offset (which is an approximation of the offset
27、 nodemethod, to be documented if utilized). As an example, the modeling of a +8 mm femoral head offset is shown here. Figures are for illustration purposesonly.F2996 1328. Analysis8.1 The analysis and modeling system, programs, or soft-ware used for the finite element model creation and analysisshou
28、ld be capable of fully developing the geometric featuresand idealizing the loading and boundary condition environmentFIG. 2 Boundary Condition Location for Hip Stem Length #120 mmNOTE 1CT: Distance between center of the head and the most distal point of the stem.FIG. 3 Boundary Condition Location fo
29、r Hip Stem Length of 120 mm 250 mmNOTE 1CT: Distance between center of the head and the most distal point of the stem.F2996 134CAD geometry file by name and revision number. If theevaluation is not being performed on the final design of thedevice or if there are other significant assumptions that ma
30、ylimit the use of the results, this must be clearly stated.(2) A description of boundary constraints, loads, and ma-terial properties. The source of the material property datautilized should be referenced.FIG. 5 Typical Maximum Principal Stress Plots for the Driver Hole, Potting Level, and NeckF2996
31、 135(3) A summary of the finite element modeling and analysissystem used for the analysis. If current versions of widely used,commercially available software are used, this summary can beby name and reference to the version used. For non-commercially available, proprietary tools, or customer usermod
32、ification of commercially available software, sufficienttechnical background and results of test problems should beprovided to demonstrate the utility, verification, applicability,and limitations of the software tool.(4) A description of the procedure used to convert thegeometric or CAD representati
33、on of the device to the finiteelement model. Any geometry simplifications should be docu-mented.(5) A description of the finite element model and itsrelation to the device being evaluated. The number of nodesand elements (or the degrees of freedom in the model), thefinite element type selected inclu
34、ding its capabilities, and anyspecial considerations involved in the model should be in-cluded. For each region of interest, the maximum (1st) principalstress and von Mises stress at the location of maximum (1st)principal stress shall be reported.(6) A description of mesh convergence considerations
35、andhow they were applied to the analysis.(7) A description of any numerical considerations or con-vergence criterion associated with the analysis.(8) A summary of analysis results using all appropriateforms of text, graphics, and tabular representations of data tohighlight the key behavioral charact
36、eristics involved in theevaluation.(9) Engineering conclusions or recommendations as appro-priate.(10) Deviations from this standard.(11) All relevant references and supporting documentationand drawings.10. Precision and Bias10.1 The precision and bias of this practice has not beenestablished.11. Ke
37、ywords11.1 computational simulations; displacements; FEA; finiteelement analyses; model calibrations; model validations;model verifications; orthopaedic implants; solution sensitivity;strains; stressesAPPENDIXES(Nonmandatory Information)X1. ROUND ROBIN STUDYX1.1 Around-robin study was performed with
38、 seven labs ona representative hip stem model (refer to Figs. 1-4 for geom-etry) following the procedure in this practice. The length of thestem falls into the category depicted by Fig. 3 of this practice.Afemoral head offset analyzed coincided with the center of thecircular area at the proximal tip
39、 of the trunnion was evaluated(that is, no trunnion extension or contraction was considered).The model was assumed to have a modulus of elasticity (E) of113.7 GPa and Poissons ratio () of 0.3. The neck, driver hole,and potting level regions were evaluated (Fig. 5). The maxi-mum percent difference fr
40、om the overall average was less than8%(Tables X1.1 and X1.2).X1.2 A laboratory study comparing stresses at the neck andpotting level determined from strain gage measurements tothose calculated from FEA on four commercially available hipstems was performed at one lab. The average differencebetween th
41、e measured and calculated stresses for the differenthip stems was 4.24 % (Table X1.3). Details of the methodologyused are provided in Appendix X2.X1.2.1 A similar study comparing strains at the neck andpotting level determined from strain gage measurements tothose calculated from FEA was performed a
42、t a second lab on arepresentative hip stem. The average difference between themeasured and calculated strains for the hip stem was 4.2 %(Table X1.4). Details of the methodology used are provided inAppendix X2.X1.2.2 The magnitude of the differences seen in bothstudies was consistent with the range o
43、f 3 to 7 % reported byPloeg, et al.4X1.3 The CAD model that was analyzed during the roundrobin is available from download at http:/www.astm.org/4Ploeg, H. L., Buergi, M., and Wyss, U.P., “Hip Stem Fatigue Test PredictionInternational Journal of Fatigue 31, 2009, pp. 894905.TABLE X1.1 Round Robin FEA
44、 Model ResultsMaximumPrincipal Stress (ksi)NOTE 1(1) all laboratories used tetrahedral elements, and (2) alllaboratories used the recommended convergence criterion of 5%.However, also note that the 5 % convergence criterion was not necessarilyperformed at each region of interest in the round robin.
45、It is recommendedthat when using this practice that the model convergence within eachregion of interest be 5 %. Reporting of the degrees of freedom is notnecessary if the model satisfies the convergence criterion.Round Robin Participant Neck Region Driver HoleRegionPotting LevelRegionCompany 1 59.9
46、26.5 25.3Company 2 61.7 27.3 24.3Company 3 62.6 28.2 24.5Company 4 57.3 25.5 24.3Company 5 59.3 24.3 22.9University 1 58.5 24.0 24.5University 2 58.6 26.3 23.2Average 59.7 26.0 24.1Standard Deviation 1.9 1.5 0.8F2996 136COMMITTEE/F04.htm. Given this CAD model, an analystcan develop a finite element
47、model consistent with that used inthe ASTM Round Robin. Loading and boundary conditionapplication, as well as a mesh convergence study, can then beperformed utilizing the method outlined in this practice. Theexpectation is the user will obtain results that are consistentwith those reported in Tables
48、 X1.1 and X1.2.TABLE X1.3 Percent Difference Between Strain GageMeasured and FEA Calculated Stresses on Four Different HipStemsFinish Material Location % DifferenceGrit blasted Ti-6Al-4V potting level 1.90 %neck level 7.40 %Sintered, gritblastedTi-6Al-4V potting level 4.70 %neck level 1.80 %Machined
49、 Ti-6Al-4V potting level 4.10 %neck level 7.30 %Polished CoCr potting level 6.20 %neck level 0.50 %Average 4.24 %TABLE X1.4 Percent Difference Between Strain GageMeasured and FEA Calculated Strains on a Representative HipStemLocation Physical TestStrain, %FEA AveragedMax PrincipalStrain, % DifferenceUsing AveragedFEA BasedStrainFemoral neck 0.0929 0.0983 5.5 %Femoral body,lateral face at70 mm level0.0875 0.0900 2.8 %Average 4.2 %X2. A COMPARISON OF FEA-BASED STRAIN RESULTS TO CONVENTIONAL STRAIN GAGE MEASUREMENTSX2.1 Introduction:X2.1.1 The purpose of this expe
