3 RAM-T Overview What is RAM-T System Design Constraints Reliability - The ability of a system or component to perform its required functions under stated conditions for a specified period of time.Availability – the ability of a product to be ready for use when the customer wants to use it (uptime/uptime+downtime)Maintainability - the relative ease and economy of time and resources with which an item can be retained in, or restored to, a specified condition when maintenance is performed by personnel having specified skill levels, using prescribed procedures and resources at prescribed level of maintenance and repair.Testability – A design characteristic which allows the status (operable, inoperable or degraded) of an item to be determined and the isolation of failures within the item to be performed in a timely manner.System Design Constraints
4 Legacy Methods Perform predictions Address SOME RAM-T drivers Legacy ApproachEliminate some component RAM-T driversFix integration issuesUpdate designEliminate some component RAM-T driversFix integration issuesUpdate designLate identification of component RAM-T shortcomingslimits corrective actionSystem Intand TestAssessmentsSubsystem IntPreliminary DesignDetailed DesignTestFieldingPerform predictionsBased on handbook dataBased on similar equipmentAddress SOME RAM-T driversRAM-T optimized during testLow initial RAM-THigh test hours, high $’s
5 Of Failed Tests, 75 % Of Systems Failed to Achieve Even Half Of Their Legacy ResultsOnly 30% Success(Data Oct 01)Of Failed Tests, 75 % Of Systems Failed to Achieve Even Half Of TheirRequirement!
6 Paradigm Shift: RAM-T Case Legacy methodologies failingMethodology required for infusing RAM-T into designCriteriaEarly, influence design during design phaseReturn on Investment (ROI)Result: Paradigm Shift – RAM-T CaseMake case for how RAM-T requirements will be metCombination of analyses and testsPhysics of Failure (PoF) analysesRAM-T Enhancement Tests (RET)RAM-T Case Management PlanRAM-T Case ReportElevate RAM-T constraint importance
7 Paradigm ShiftLegacy ApproachEliminate some component RAM-T driversFix integration issuesUpdate designEliminate some component RAM-T driversFix integration issuesUpdate designLate identification of component RAM-T shortcomingslimits corrective actionSystem Intand TestAssessmentsSubsystem IntPreliminary DesignDetailed DesignTestFieldingRAM-T Case ApproachEliminate component reliability driversUpdate designFix integration issuesUpdate designEliminate component reliability driversUpdate designFix integration issuesUpdate designEarly identification and elimination of component level failuresSystem Int and TestPoFRETSubsystem IntEmphasize: Early identification and elimination of RAM-T shortcomingsExample: Achieve Higher Mi on prototype delivery
8 Paradigm Shift: RAM-T Case Make case for meeting RAM-T requirementsDocumented in RAM-T Case Management PlanA living document, updated throughout the programPlan and supporting data subject to approvalRAM-T requirements are clearly understoodMethods/activities to be performed to make caseEnsure RAM-T is key factor in the design processEnsure RAM-T is of equal weight with other engineering disciplinesRAM-T Case ReportReasoned, auditable documentation of progressive assurance that RAM-T requirements will be metAudit trail of engineering considerations, trade studies, analyses and assessments
9 Paradigm Shift: RAM-T Case A RAM-T Case Program/Plan sample contentsBenchmarking RAM-T RequirementsDynamic/static design modeling, simulation, or probabilistic analysisCritical component identificationRAM-T Modeling, Optimization and Component/System TestingEnvironmental stress (operate and storage)Physics-of-Failure (PoF)Structural finite-element stress analysisFatigue analysisWear-out/service life analysisLong-term storage (shelf life) assessmentPrognostics analysisFault detection/isolation analysisBuilt-in Test False alarm rate analysisAvailability AnalysisOn-board Sparing: Supportability analysisRAM-T Block DiagramRAM-T Assessments AnalysisRisk assessment & mitigationDiminishing resources/obsolescence planPit Stop Engineering
10 Paradigm Shift: RAM-T Case RAM-T Case Management PlanMethods/activities to be performed to make caseGoal - Robust designsPhysics of Failure (PoF)Finite Element Analysis (FEA)Fatigue AnalysisProbabilistic AnalysiscalcePWA AnalysisPit-Stop EngineeringRAM-T Enhancement Testing (RET)Highly Accelerated Life Testing (HALT)Accelerated Life Testing (ALT)
11 Engineering-Based Reliability Physics of Failure,-Model the root causes of failure (e.g., fatigue, fracture, corrosion & wear)CAD tools developed- By industry/academia/government- To address specific materials, sites, &architecturesStress (e.g., vibration) is propagated from system level to failure sitePhysics of failure is a science-based approach to addressing reliability in the design process. Physics-of-failure is an approach to developing reliable products that uses knowledge of basic failure processes to prevent product failures through robust design and manufacturing practices. This approach incorporates reliability into the design process by establishing a scientific basis for evaluating new materials, structures, and electronics technologies.By understanding the basic causes of failure, or failure mechanisms, the design engineers can use this information to reduce and focus reliability testing.The greatest benefit of physics of failure is the insight it provides into reliability throughout the expected life cycle of a system. This insight provides the ability to predict the reliability of the design before the system is built and to assess the reliability of commercial components. The bottom line is that the use of physics of failure leads to an increase in system reliability. This increase in system reliability enhances system availability and decreases cost. Not only can physics of failure decrease acquisition cost, but it can also decrease operations and support costs.BenefitsDesign-in reliabilityEliminate failures prior to testIncreased fielded reliabilityDecreased O&S costsRoot-cause failure is cracking of solder joint
12 Software Tools Finite Element Modeling Solid Modeling Dynamic SimulationAMSAA has or will be utilizing several software tools to complete PoF-based analyses of Army electronics and mechanical systems. The most employed tool has been the U. of Maryland’s Electronic Packaging Research Center’s (EPRC) CCA-level CalcePWA toolkit. This toolkit allows for integrated vibration and thermal analyses of CCAs and utilizes PoF-based models of solder-joint fatigue and PTH fatigue to predict the fatigue lives and reliability of CCAs.Another EPRC toolkit that has been used by AMSAA is the device (or IC) level CADMP (Computer-Aided Design of Microelectronic Packages) toolkit. CADMP is a set of integrated software programs that can be used to design and assess the reliability of both single chip packages and multichip modules (MCMs). CADMP utilizes PoF methodology to assess reliability and do trade-off analyses by investigating over 40 different failure mechanisms, failure sites, and root causes of failures.The DROW (Durability and Reliability Optimization Workspace) is a mechanical PoF-based toolkit developed at the U. of Iowa’s Center for Computer Aided Design, which AMSAA plans to utilize in a future mechanical PoF demonstration program. DROW utilizes rigid or flexible body dynamics simulation and commercial FEA codes to develop stress states on mechanical designs, and predict reliability based on specified operational conditions.Electronic Circuit Card and IC ToolkitsFatigue AnalysisThermal Fluid Analysis
13 Physics of Failure to Evaluate Electronics Enclosure DesignCircuit Card DesignVibration/Shock EnvironmentComputationalFluidDynamics ModelCalcePWACircuit CardToolThermal ConditionsDetermine if electronics are acceptable based on analysisDetermine if circuit card or enclosure can be redesigned to eliminate failure mechanismPhysics-of-failure uses knowledge of root cause failure processes to prevent product failures through robust design and manufacturing practices. This approach involves the following steps:examine the operational/environmental loads and the preliminary design, identify potential failure mechanisms (chemical, electrical, physical, mechanical, structural, or thermal processes leading to failure); failure sites; and failure modes (which result from the activation of failure mechanisms, and are usually precipitated as shorts, opens, or electrical deviations beyond specifications);perform a stress analysis on the stresses (e.g., thermal, vibrational, shock, humidity, & current) that accelerated the potential failure mechanisms;identify the appropriate failure models and their input parameters, including those associated with material characteristics, damage properties, relevant geometry at failure sites, manufacturing flaws and defects, and environmental and operating loads;determine the variability for each design parameter when possible;predict the time-to-failure, or life of the potential failure mechanisms;perform accelerated life testing to verify that the potential failure mechanisms will occur, to verify the stress/life relationship (failure mechanism model), and to determine if unexpected failure mechanisms would occur.accepting the design, if the life is acceptable, re-design failure mechanisms out of the life cycle, or use preventative maintenance (prognostics) to replace the equipment before it causes a system failure.PoF-Based ESSAccelerated Life Testingon critical board or IC failure mechanisms
14 Computational Fluid Dynamics (CFD) Modeling Examples: ICEPAK, FLOWMAX, University of Maryland CalceCFDInputsExterior ambient air temperatureInitial temperatureFan propertiesPower dissipated for each CCAOutputsInterior air velocityInterior air temperatureCCA edge temperatureIn order to determine internal enclosure temperatures of the BFCC at different power loads, a commercial CFD solver known as ICEPAK was utilized to calculate and graphically display temperature distributions within the enclosure walls. The first step in developing the appropriate CFD model for this study was to determine what results were expected from the solver. Based on the fact that the PM was concerned with the internal temperatures of the enclosure, it was determined that not all of the features of the BFCC would necessarily have to be modeled. Therefore, in order to simplify the model the air flow through the finned side wall channels was not modeled. Instead, a forced convection boundary layer along either side of the enclosure with a constant convection coefficient of 170 W/m2-oC per side was used in the analysis. This constant was determined to be a conservative representation of a 50 Cubic Feet per Minute (CFM) flow over aluminum plain fins with dimensions of 17.5x5.25x0.5 inches with 14 fins per inch and 0.01 inch thickness. Also, the effects of radiation were assumed to be negligible for determining the internal feature temperatures. These assumptions allowed the CFD modeling to focus more on the conduction and convection resistive networks within the BFCC and less on the external features of the BFCC such as air flow through the fins.Therefore, the features of the BFCC modeled in ICEPAK included only the cold plate structure, the powered CCA board structures (to include an aluminum heatsink layer and a FR-4 epoxy layer), and the six sheet metal panels that enclose the internal features of the BFCC. The power load applied to each CCA was distributed evenly among corresponding finite elements of each card.Outputs from CFD analysis used as boundary conditions for CCA thermal modeling
15 UMD CalcePWA Software Tool Architecture & environmentmodelingReports and documentationToolboxFailure assessment& sensitivity analysisVibration analysisThermal analysisCalcePWA is a CCA-level toolkit developed at the U. of Maryland’s Electronic Products and Systems Center (ESCC) that contains several stress assessment tools and PoF-based fatigue models to predict the reliability of CCAs. The toolkit contains an integral finite difference-based thermal analysis tool that analyzes component temperatures and the board-level temperature distributions based on several different operator selected cooling mechanisms. It also contains an integral finite element analysis (FEA)-based vibration modal analysis tool that determines the fundamental resonant frequencies of the board, the corresponding mode shapes, and maximum displacement of the board. These integral stress analysis tools identify the stresses present on the board for any given boundary condition, and develop the input to the solder-joint and plated through-hole (PTH) fatigue analysis models. These fatigue analysis models utilize this stress data to predict the fatigue life of the component solder-joints and PTHs. The toolkit can be used to do any number of trade-off studies, and has been used in that fashion to validate the use of commercial components for certain military environments.Future extensions of CalcePWA include a humidity stress analysis tool, a conductive filament formation model (in latest version - metal growth from one conducting metal line to another through the board, which causes a short circuit), and a metal line corrosion model (causes signal distortion).
16 Electronics Circuit Card Success Stories Tracked VehicleIncreasedReliability$1.2M SavedRadar Ground StationIdentified potential thermal & vibration problemsAnalysis showed commercial circuit card OK$27M CostAvoidanceAir & Ground System ElectronicsTri-Service RadioDesign ChangesRecommendedIdentified weak link in design & verifiedValidated with testingCircuit card & thermal box-level analysesIdentified problems & ensured reliable expansion of capabilityArmy Helicopter$50MSavingsMissile SystemAir Force analysis showed commercial ICs OKAnalysis on Plastic Ball Grid Array IC packageEvaluate New Technology
17 Fatigue Analysis Using Dynamic Simulation & FEA Solid ModelingDynamic Load AnalysisTerrain ModelSystem ModelDynamics AnalysisDADSPro/EComponent Stress AnalysisFE ModelFEANASTRANReliability AnalysisReliability BasedDesign OptimizationFatigue Life AssessmentList of Critical NodesDRAW
18 Three-Dimensional CAD Solid Models CAD: Pro/Engineer, AUTOCAD, I-deas, Solidworks,Used for design and manufactureUsed to develop Finite Element Analysis & Dynamic Analysis models
19 Finite Element Analysis (FEA) Models Examples: NASTRAN, ANSYS, ABACUS, Pro/Mechanica, I-deasCalculates vibration modesCalculates stress and strainInput into fatigue analysisUsed for structural stress evaluationMode 2
20 Flexible-Body Dynamic Analysis Model Examples: DADS & ADAMSMulti-body approachUse input from solid model & FEA modelExperimental data used for model inputs of tire, shock absorbers & suspensionDetermines force/ acceleration time history at all locations on trailerVehicle traversing simulated terrain profileInput into FEA & fatigue analyses
21 Fatigue Analysis Software Examples: nCode, LMS, University of Iowa DRAWEdits & characterizes strain time historiesRainflow counting & mean stress correction of strain cyclesEstimates plastic strain based on elastic stress or strain calculationsCalculates fatigue life based on measured (strain gauge) or FEA strain time histories
22 Trailer Physics-of-Failure Project Fatigue life estimates of drawbar consistent with failure dataCritical PointLife (Blocks)White represents low fatigue lifeBenefits:Early identification of failure modesBetter test planning and designImproved maintenance proceduresEnlargement ofCritical Region
23 Paradigm Shift: RAM-T Case Pit-Stop EngineeringUser/Maintainer hardware interface as a key design parameterDevelop Standards of ExcellenceDefines the critical parametersExamples37 pounds maximum for an electrical assembly.Spares on board to provide on board failure recovery.Placement of electronics should be on exterior man accessible surfaces, no buried electronics.No cables in places where they cannot be accessed.Use common connectors throughout.Etc.Visualization for decision making
27 Paradigm Shift: RAM-T Case Reliability Enhancement Testing (RET)Testing focused on Reliability improvementObjectiveFind failure modesEliminate failure modesMitigate those not able to eliminatePeriod of performanceOnce hardware is availableMethodologiesUse up the life of the productNormal use (years)Accelerated life test (weeks or months)Highly accelerated life test (days)
29 Paradigm Shift: RAM-T Case Environmental Stress Chamber with Unit Under Test (UUT) Powered-up and Functioning under loadTest Equipment Providing real-time status of UUT performance
30 Embrace the philosophy Determine critical items ImplementationEmbrace the philosophyDetermine critical itemsPut together multi-disciplined teamReliability Improvement Working Group (RIWG)Determine RAM-T Case methodologiesDocument in Action Plan
31 Reliability Improvement Working Groups ImplementationReliability Improvement Working GroupsIntegrated, collaborative team composed of design, specialty, and test personnel to develop Action Plans for critical components to improve the reliability early in the design process.Action Plans cover proactive reliability tasks such as design reviews, load/stress surveys, failure mode analysis, physics of failure, probabilistic analysis, and reliability enhancement testing.Forum for discussing Action Plans with and receiving input from reliability improvement experts from customer, OPM, AMSAA, AEC, and other government and industry organizations.
32 ImplementationRisk Mitigation & Proactive Reliability TasksNote: Planned through March 2004 unless otherwise indicatedNote (1): Planned by PDR
33 The gaps show that the whole surface area is not being used to seal. ImplementationEmerging Findings, Physics of Failure, FEARecoil SealThe gaps show that the whole surface area is not being used to seal.
34 RIWG Projected Costs Result: Influenced material selection Emerging Findings, RETRammer Chain Housing MaterialMaterial SampleResult: Influenced material selectionSignificant parameters: Wear and heat buildup