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System Design Constraints, RAM-T, a Paradigm Shift

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Presentation on theme: "System Design Constraints, RAM-T, a Paradigm Shift"— Presentation transcript:

1 System Design Constraints, RAM-T, a Paradigm Shift
Vern Fox United Defense LP

2 Agenda RAM-T Overview Legacy Methods Legacy Results
Paradigm Shift: RAM-T Case Implementation

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 Approach Eliminate some component RAM-T drivers Fix integration issues Update design Eliminate some component RAM-T drivers Fix integration issues Update design Late identification of component RAM-T shortcomings limits corrective action System Int and Test Assessments Subsystem Int Preliminary Design Detailed Design Test Fielding Perform predictions Based on handbook data Based on similar equipment Address SOME RAM-T drivers RAM-T optimized during test Low initial RAM-T High test hours, high $’s

5 Of Failed Tests, 75 % Of Systems Failed to Achieve Even Half Of Their
Legacy Results Only 30% Success (Data Oct 01) Of Failed Tests, 75 % Of Systems Failed to Achieve Even Half Of Their Requirement!

6 Paradigm Shift: RAM-T Case
Legacy methodologies failing Methodology required for infusing RAM-T into design Criteria Early, influence design during design phase Return on Investment (ROI) Result: Paradigm Shift – RAM-T Case Make case for how RAM-T requirements will be met Combination of analyses and tests Physics of Failure (PoF) analyses RAM-T Enhancement Tests (RET) RAM-T Case Management Plan RAM-T Case Report Elevate RAM-T constraint importance

7 Paradigm Shift Legacy Approach Eliminate some component RAM-T drivers Fix integration issues Update design Eliminate some component RAM-T drivers Fix integration issues Update design Late identification of component RAM-T shortcomings limits corrective action System Int and Test Assessments Subsystem Int Preliminary Design Detailed Design Test Fielding RAM-T Case Approach Eliminate component reliability drivers Update design Fix integration issues Update design Eliminate component reliability drivers Update design Fix integration issues Update design Early identification and elimination of component level failures System Int and Test PoF RET Subsystem Int Emphasize: Early identification and elimination of RAM-T shortcomings Example: Achieve Higher Mi on prototype delivery

8 Paradigm Shift: RAM-T Case
Make case for meeting RAM-T requirements Documented in RAM-T Case Management Plan A living document, updated throughout the program Plan and supporting data subject to approval RAM-T requirements are clearly understood Methods/activities to be performed to make case Ensure RAM-T is key factor in the design process Ensure RAM-T is of equal weight with other engineering disciplines RAM-T Case Report Reasoned, auditable documentation of progressive assurance that RAM-T requirements will be met Audit trail of engineering considerations, trade studies, analyses and assessments

9 Paradigm Shift: RAM-T Case
A RAM-T Case Program/Plan sample contents Benchmarking RAM-T Requirements Dynamic/static design modeling, simulation, or probabilistic analysis Critical component identification RAM-T Modeling, Optimization and Component/System Testing Environmental stress (operate and storage) Physics-of-Failure (PoF) Structural finite-element stress analysis Fatigue analysis Wear-out/service life analysis Long-term storage (shelf life) assessment Prognostics analysis Fault detection/isolation analysis Built-in Test False alarm rate analysis Availability Analysis On-board Sparing: Supportability analysis RAM-T Block Diagram RAM-T Assessments Analysis Risk assessment & mitigation Diminishing resources/obsolescence plan Pit Stop Engineering

10 Paradigm Shift: RAM-T Case
RAM-T Case Management Plan Methods/activities to be performed to make case Goal - Robust designs Physics of Failure (PoF) Finite Element Analysis (FEA) Fatigue Analysis Probabilistic Analysis calcePWA Analysis Pit-Stop Engineering RAM-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, & architectures Stress (e.g., vibration) is propagated from system level to failure site Physics 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. Benefits Design-in reliability Eliminate failures prior to test Increased fielded reliability Decreased O&S costs Root-cause failure is cracking of solder joint

12 Software Tools Finite Element Modeling Solid Modeling
Dynamic Simulation AMSAA 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 Toolkits Fatigue Analysis Thermal Fluid Analysis

13 Physics of Failure to Evaluate Electronics
Enclosure Design Circuit Card Design Vibration/Shock Environment Computational Fluid Dynamics Model CalcePWA Circuit Card Tool Thermal Conditions Determine if electronics are acceptable based on analysis Determine if circuit card or enclosure can be redesigned to eliminate failure mechanism Physics-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 ESS Accelerated Life Testing on critical board or IC failure mechanisms

14 Computational Fluid Dynamics (CFD) Modeling
Examples: ICEPAK, FLOWMAX, University of Maryland CalceCFD Inputs Exterior ambient air temperature Initial temperature Fan properties Power dissipated for each CCA Outputs Interior air velocity Interior air temperature CCA edge temperature In 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 & environment modeling Reports and documentation Toolbox Failure assessment & sensitivity analysis Vibration analysis Thermal analysis CalcePWA 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 Vehicle Increased Reliability $1.2M Saved Radar Ground Station Identified potential thermal & vibration problems Analysis showed commercial circuit card OK $27M Cost Avoidance Air & Ground System Electronics Tri-Service Radio Design Changes Recommended Identified weak link in design & verified Validated with testing Circuit card & thermal box-level analyses Identified problems & ensured reliable expansion of capability Army Helicopter $50M Savings Missile System Air Force analysis showed commercial ICs OK Analysis on Plastic Ball Grid Array IC package Evaluate New Technology

17 Fatigue Analysis Using Dynamic Simulation & FEA
Solid Modeling Dynamic Load Analysis Terrain Model System Model Dynamics Analysis DADS Pro/E Component Stress Analysis FE Model FEA NASTRAN Reliability Analysis Reliability Based Design Optimization Fatigue Life Assessment List of Critical Nodes DRAW

18 Three-Dimensional CAD Solid Models
CAD: Pro/Engineer, AUTOCAD, I-deas, Solidworks, Used for design and manufacture Used to develop Finite Element Analysis & Dynamic Analysis models

19 Finite Element Analysis (FEA) Models
Examples: NASTRAN, ANSYS, ABACUS, Pro/Mechanica, I-deas Calculates vibration modes Calculates stress and strain Input into fatigue analysis Used for structural stress evaluation Mode 2

20 Flexible-Body Dynamic Analysis Model
Examples: DADS & ADAMS Multi-body approach Use input from solid model & FEA model Experimental data used for model inputs of tire, shock absorbers & suspension Determines force/ acceleration time history at all locations on trailer Vehicle traversing simulated terrain profile Input into FEA & fatigue analyses

21 Fatigue Analysis Software
Examples: nCode, LMS, University of Iowa DRAW Edits & characterizes strain time histories Rainflow counting & mean stress correction of strain cycles Estimates plastic strain based on elastic stress or strain calculations Calculates 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 data Critical Point Life (Blocks) White represents low fatigue life Benefits: Early identification of failure modes Better test planning and design Improved maintenance procedures Enlargement of Critical Region

23 Paradigm Shift: RAM-T Case
Pit-Stop Engineering User/Maintainer hardware interface as a key design parameter Develop Standards of Excellence Defines the critical parameters Examples 37 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

24 Paradigm Shift: RAM-T Case

25 Paradigm Shift: RAM-T Case

26 Paradigm Shift: RAM-T Case

27 Paradigm Shift: RAM-T Case
Reliability Enhancement Testing (RET) Testing focused on Reliability improvement Objective Find failure modes Eliminate failure modes Mitigate those not able to eliminate Period of performance Once hardware is available Methodologies Use up the life of the product Normal use (years) Accelerated life test (weeks or months) Highly accelerated life test (days)

28 Paradigm Shift: RAM-T Case
Load Levels Upper Destruct Limit Upper Operating Limit Upper Design Limit Upper Specification Limit Lower Specification Limit Lower Design Limit Lower Operating Limit Lower Destruct Limit Nominal Upper Design Margin Lower Design Upper Destruct Lower Destruct Upper Operating Lower Operating

29 Paradigm Shift: RAM-T Case
Environmental Stress Chamber with Unit Under Test (UUT) Powered-up and Functioning under load Test Equipment Providing real-time status of UUT performance

30 Embrace the philosophy Determine critical items
Implementation Embrace the philosophy Determine critical items Put together multi-disciplined team Reliability Improvement Working Group (RIWG) Determine RAM-T Case methodologies Document in Action Plan

31 Reliability Improvement Working Groups
Implementation Reliability Improvement Working Groups Integrated, 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 Implementation Risk Mitigation & Proactive Reliability Tasks Note: Planned through March 2004 unless otherwise indicated Note (1): Planned by PDR

33 The gaps show that the whole surface area is not being used to seal.
Implementation Emerging Findings, Physics of Failure, FEA Recoil Seal The gaps show that the whole surface area is not being used to seal.

34 RIWG Projected Costs Result: Influenced material selection
Emerging Findings, RET Rammer Chain Housing Material Material Sample Result: Influenced material selection Significant parameters: Wear and heat buildup

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