Why Things Break (and how we try to make sure they don’t!)

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Why Things Break (and how we try to make sure they dont!). Robert Love, Venkat Jayaraman July 10, 2008 SSTP Seminar Lecture 6. Overview. Presentation Analysis Statics Mechanics of Materials Finite Element Analysis (Method) Testing Methods Production Industrial Quality Practice - PowerPoint PPT Presentation

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Why Things Break (and how we try to make sure they dont!)Robert Love, Venkat JayaramanJuly 10, 2008SSTP Seminar Lecture 6UF Flight Controls LabOverviewPresentationAnalysisStaticsMechanics of MaterialsFinite Element Analysis (Method)Testing MethodsProductionIndustrial Quality PracticeFailure Mode and Effect Analysis (FEMA)Statistical Process Control (SPC)Six SigmaPost-MortemFailure AnalysisDiscussionActivity*UF Flight Controls Lab*UF Flight Controls LabStaticsNet force = 0Free Body DiagramsExternal ForcesBasic StructureTrusses, MembersConstraintsCommon: Fixed, Pin, Roller*UF Flight Controls Lab*UF Flight Controls LabLoading and BCs*UF Flight Controls Lab*UF Flight Controls LabMechanics of MaterialsExternal Loading Determines Internal LoadingShear and Moment DiagramsCross Section CharacteristicsCentroid vs. Center of MassMoment of InertiaMUST be given about an axis!*UF Flight Controls Lab*UF Flight Controls LabMechanics of MaterialsInternal StressesShear vs. Axial StressBending vs. TorsionRepresented by Stress Tensor*UF Flight Controls Lab*UF Flight Controls LabTestingDestructive (see below) vs. Non-Destructive (ex: dye penetrant)Tensile Strength: Tensile Tester (also for fatigue)Impact Strength: Charpy/Izod Testing (temp. variations)Hardness: Vickers/Rockwell/Brinell Scale w/Indenter Creep: Creep Test RigFatigue: Fatigue Tester*UF Flight Controls Lab*UF Flight Controls LabFinite Element AnalysisTypes of Elements1D: Bar, Beam2D: Quadrilateral, Triangle3D: Tetrahedral, HexahedralMay use multiple NodesStatic or Dynamic AnalysisStatic Load or Modal AnalysisCommon FEA ProgramsPatran/Nastran, Abaqus, Pro-E Mechanica, Ansys*UF Flight Controls Lab*UF Flight Controls LabQuality assurance is the set of planned and systematic actions necessary to provide appropriate confidence that a product or service will satisfy the requirements for quality. Quality assurance activitiesFailure testing Operation of a product until it failsExposes many unanticipated weakness in the productStatistical Process ControlEffective method of monitoring a process through the use of tools like control chartsIndustrial Quality Practices UF Flight Controls LabFMEA A tool used to comprehensively analyze and fix a failure of a product or process.DefinitionsFailure mode - The way the failure occurs Failure Effect The immediate consequence of the failure modeSeverity(1-10) Degree of worst potential consequenceOccurrence(1-10) Estimate of number of chances a failure mode can occur Detection(1-10) Degree of ease of detection of the failure modeRisk Priority Number Product of Severity, Occurrence and DetectionFailure Mode and Effect Analysis (FMEA) UF Flight Controls LabFailure Mode and Effect Analysis (FMEA) FMEA Flow ChartSample FMEA WorksheetUF Flight Controls LabSPC - involves using statistical techniques to measure and analyze the variation in processes. Statistical Process Control(SPC)Control ChartUF Flight Controls LabProcess CapabilityVoice of CustomerVoice of ProcessThis curve is the distribution of data from the processThe shaded areas represent the percentage of off-specproductionIdeally, you want to reduce the variability in the product until NO off-spec product is made.UF Flight Controls LabSix Sigma process is one that produces 3.4 defective parts per million opportunities Basic MethodologyDefine Process ImprovementMeasure key aspects Analyze cause-effect relationshipsOptimize the processControl the processImplementation key rolesExecutive leadershipChampionsMaster black beltsBlack beltsGreen beltsYellow beltsSix SigmaTraditionalAfter Six SigmaUF Flight Controls LabFailure AnalysisWhat was the failure mode? Hint: Look at the surface (even under a microscope)!Visualize how the material brokeUse your knowledge of material bonding and possible loading conditions to understandLook for evidence of other effectsKnow so that can prevent recurrenceEngineers as expert witnesses *UF Flight Controls Lab*Ex: ImpactUF Flight Controls LabFailure AnalysisSome types of failuresFracture (brittle or ductile)ImpactBuckling FatigueCorrosion High TemperatureBending TorsionShearVibrationResonance/FlutterCreepDelaminationWeak Bonding/Joint/Weld*UF Flight Controls Lab*UF Flight Controls LabActivityFinite Element Analysis ProcedureDefine CAD ModelDefine Boundary ConditionsDefine Loading ConditionsDefine Material PropertiesDiscretize model (make a mesh of finite elements)Run AnalysisVisualize Analysis*UF Flight Controls Lab*UF Flight Controls LabActivity14.1GPa=Youngs Modulus,E (tensile)0.25=Poissons Ratio, nu1900kg/m3=density*UF Flight Controls Lab*UF Flight Controls Lab*We may not be presenting this in an intuitive enough way even stilltoo much mathematical modeling?-Still desire to give them an adequate picture of what engineering is*Write out must sum forces in all directions!*Point load vs. distributed load, forces and moments, boundary conditions, an applicationTorque=moment=r cross F*Centroid: average of all points, also center of mass if uniform density: most CAD software will calculate for you nowBreak into multiple parts, then find centroid of entire cross section-where gravity acts on if = center of massUnderstand golf clubs and tennis rackets from this perspective!http://homepages.ed.ac.uk/dtheodo1/S_CG2_resources/stress_distr.jpghttp://www.roymech.co.uk/Useful_Tables/Beams/Shear_Bending.htmlhttp://www.see.leeds.ac.uk/structure/dynamicearth/internal/moment/inertia.gif*https://ecourses.ou.edu/cgi-bin/ebook.cgi?doc=&topic=st&chap_sec=03.3&page=case_introhttp://www.fzk.de/fzk/groups/imf-2/documents/internetdokument/~export/ID_052585~1~WORD/6640-8.jpghttp://www.amtec.com/images/showcase/contours/issue_3/01_aneurysm.jpghttp://www.efunda.com/formulae/solid_mechanics/mat_mechanics/images/StressState3D.gifhttp://www.archoneng.com/tptasm.html*http://www.twiprofessional.com/twiimages/jk71f2.gifhttp://www.brystartools.com/catalog/4JS%20SN1644%20681.jpg*http://www.gearhob.com/eng/fe.htm: programshttp://www.colorado.edu/engineering/CAS/courses.d/IFEM.d/IFEM.Ch06.d/IFEM.Ch06.pdf: introduction*It includes the regulation of the quality of raw materials, assemblies, products and components; services related to production; and management, production, and inspection processes *Reality of escaping defectsEven the most careful inspection misses sometimesBad product means unhappy customersInspection costs moneyRejection wastes resourcesReworking/scrapping wastes time, money, and resourcesIntuition and gut feelings work for . . .Simple problemsInexpensive solutionsLow risk in case of failureStatistical evaluation works for . . .Complex problemsExpensive solutionsHigh risk in case of failure**http://www.seidowestpalmbeach.com/images/Kaicho%20Ice%20Break.jpg*plastic vs. elastic deformation, crack growth and propogationhttp://www.benbest.com/cryonics/sscurve.gifhttp://www.auf.asn.au/const_images/stress_strain4.jpghttp://goosite.net/wp-content/uploads/2008/02/cokecrushed.jpghttp://mgoodson.com/arced%20wire%20melted.jpgFlutter:http://www.youtube.com/watch?v=ca4PgyBJAzM&NR=1http://www.youtube.com/watch?v=8D7YCCLGu5Y&feature=related*Options:Hands on broken stuff (maybe break something)Drawing Free Body DiagramsFEA in ProE-Distributed Loading (bone?)*http://www.feppd.org/ICB-Dent/campus/biomechanics_in_dentistry/ldv_data/mech/basic_bone.htmhttp://hypertextbook.com/facts/2002/AnnaYarusskaya.shtml*

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