MPD 575 Design for Failure

1. MPD 575Design for Failure

2. Developed By: Cohort Team 3: Cathy Campbell Brandon Johnson Robbin McDaniel Britt Scott Updates by Anita Bersie, Joe Torres, Beatriz Dhruna, John Haddock, Mac Lunn

3. Development History • Latest updates by many of the following students in winter of 2014: M. Freeman, H. Gasahl, R. Glaser, A. Kammerzell, J. Lambrecht, D. Mincock, J. Murphy, M. Rockwell, P. Roncier, J. Salinas, G. Scalcucci, D. Slater MPD575 Weaver

4. Design for Failure • Introduction to Design for Failure (DFF) • System Engineering V-Model and DFF • Heuristics • How DFF fits into PD Process • Situation to implement DFF • Examples • Summary

5. Design for Failure Definitions of key DFF terms: Design: Creative process in the Arts, Sciences and Technologies. There are many design heuristics that are derived from rules, relationships and experiences. Failure: A condition in which a system no longer performs its intended function, or is unable to do so at a level that meets customer satisfaction. Failure can also result from the emergence of an undesirable function. System Architecture: The art and science of creating and building complex systems. That part of systems development most concerned with scoping, structuring, and certification. [M&R, 1997]. Failure Mode And Effect Analysis (FMEA): Systematic activities intended to: 1) recognize and evaluate potential failure of products/processes and its effects 2) identify actions to eliminate or reduce the chance of the potential failure occurring 3) document the process

6. Design for Failure Definitions (cont’d) • Classification of failures: • Hard failures cause complete loss of function, (ex: Driveline does not transmit torque to wheels) • Soft failures cause degraded function, (ex: driveline whines at 45 mph steady vehicle speed. • Approach Design for failures must be approached from a functional perspective as opposed to a hardware perspective. It is recommended to use a “function tree” to decompose functions from the system to the subsystems and components.

7. Design for Failure Failure, cont’d: –Failures should be qualified and quantified. –The results of failure should be taken into account and fed back into the design process. –The most important aspect is “proper feedback”. –Failures are something engineers spend their life trying to avoid. However, there are times in which a failure is designed into the system as a function under certain conditions to maintain the integrity of other functions of the systems. –The cause of the conditions are uncontrollable by the engineers but the failure under these conditions can be controlled.

8. Design for Failure Team’s definition of DFF: “A system or component designed to fail under certain conditions or circumstances”

9. Design for Failure • Introduction to Design for Failure (DFF) • System Engineering V-Model and DFF • Heuristics • How DFF fits into PD Process • Situation to implement DFF • Examples • Summary

10. Design for Failure System design has three phases: • Design the Product or Component • Optimize the Design • Validate the Design

11. Design for Failure Design the Product or Component – Complete System Architecture analysis. For DFF specifically, the focus should be placed on identifying the architecturally significant requirements, tracing the requirements to their owners, analyzing reusable components at their interfaces, selecting, assessing and accepting the system architecture. For each tasks, a list of risks and opportunities must be updated as the architecture is refined. Failure mode management is a key driver in the selection process of the architectural vision. – Complete technical concept generation. - Complete concept DFMEA. –Complete system and component level Design. –Complete P-diagrams, identify ideal functions, error states, control factors, noise factors. –Conduct system and component DFMEA’s –Address failure modes in order of severity and then in order of the product of severity by occurrence. –Implement actions to reduce severity of failures identified as critical and unavoidable by altering primary failure modes.

12. Design for Failure • Optimize the Design – Eliminate unacceptable failure modes, including but not limited to high severity modes. Example: Fuse the front wheel driveline by notching the half-shafts (avoid high cost failures in the front wheel ends). – Substitute high severity failure modes by lower severity failure mode. Example: block with soft shackle compared to typical hard block. Failure of the shackle or the block leads to complete loss of tension in the line running through the block Soft shackle tensile strength is greater than block. Failure of the block will cause loss of maneuverability but no loss of tension. – Document trade-offs. – Iterate the designs (parallel paths if possible) through CAE and physical testing using component and system level testing until reliability is established.

13. Design for Failure • Validate the Design (Testing) –Critical noise factors (internal and external) must be included in the tests. –Duty cycle must be correlated to real life usage. –Tests must be run to failure to verify that the system failed as intended and that the system is able to perform the protected functions under the test simulated conditions. –Failure modes (primary, secondary,…) must be analyzed. –Teardown analysis are too often neglected. All parts must be inspected to properly assess the failure mechanisms. –Product validation starts at the component level and ends at the full system level.

14. Four Conditions That Can Lead to Failure Every system specification must specify requirements that address four types of system conditions: • Normal Operations (Ideal Conditions) • External System Failures • Degraded Operations • Internal System Failures

15. Conducting a DFMEA • Review the Design and Interfaces • Brainstorm potential failure modes – Review existing documentation and data for clues • List potential effects of failure • Assign Severity rankings – What is the severity of the consequences of failure? - Failures with severity 9 and 10 are potential critical characteristics. - Failures with severity 5 thru 8 are potential significant characteristics. • Assign Occurrence rankings – How frequently is the cause of failure likely to occur? • Assign Detection rankings – What are the chances that the failure will be detected prior to the customer finding it? • Calculate the RPN – Severity x Occurrence x Detection • Develop the action plan • Take Action • Calculate the resulting RPN

16. Design for Failure Definition of failure types: • Elastic failure: excessive elastic deformation • Elastic: strain resulting from the load leaves after the load has been removed • Slip failure: excessive plastic deformation due to slip. • Plastic: strain exceeds the elastic limit; a portion of the deformation remains after the load is removed • Slip: plastic deformation independent of time duration of the applied load • Creep failure: excessive plastic deformation over a long period of time under constant stress • Failure by Fracture: complete separation of the material • Thermal failure of fuse blow • Corrosion/degradation failures leading to increased resistance

17. Design for Failure Two approaches to detect failure: • Passive: detector monitors the inputs and the outputs of the system and decides whether (and if possible what kind of) a failure has occurred. This is done by comparing the measured input-output behavior with “normal” behavior of the system. • Active: The active approach to failure detection consists of acting upon the system on a periodic basis or at critical times using a test signal, auxiliary signal, in order to exhibit abnormal behaviors which would otherwise remain undetected during normal operation.

18. Design for Failure • Introduction to Design for Failure (DFF) • System Engineering V-Model and DFF • Heuristics • How DFF fits into PD Process • Situation to implement DFF • Examples • Summary

19. Design for Failure Heuristics P = Prescriptive, D = Descriptive • (D) It is better to be aware of the failures than not. • (P) You want to design a “less expensive” component to fail in order to protect a more expensive component. • (P) Understand planned failures; fail as they are planned. • (P) Failure is defined by the beholder, not by the architect.(Modification of Maier/Rechtin, 270)

20. Design for Failure Heuristics (continued) • (P) Don’t confuse the functioning of the parts for the functioning of the system. (Maier/Rechtin, 269) • (D) Some of the worst failures are system failures. (Maier/Rechtin, 271) • (P) Choose the elements so that they are as independent as possible; that is, elements with low external complexity (low coupling) and high internal complexity (high cohesion). (Maier/Rechtin, 273) • (P) The principles of minimum communications and proper partitioning are key to system testability and fault isolation. (Maier/Rechtin, 275) • (D) Knowing a failure has occurred is more important than the actual failure. (Maier/Rechtin, 276)

21. Design for Failure • Introduction to Design for Failure (DFF) • System Engineering V-Model and DFF • Heuristics • How DFF fits into PD Process • Situation to implement DFF • Examples • Summary

22. Design for Failure How DFF fits into PD Process • Gather raw data from the customers • Interpret the data in terms of customers needs. • Organize and establish the importance • Establish target specifications • Identify any potential products that require safe failure modes • Determine the strategy • Establish warranty guidelines • Include the failure strategy in overall system architecture – boundaries for failure

23. Design for Failure How DFF fits into PD Process 9. Set-up design requirements and targets 10. Define validation requirements 11. Establish assembly, service and maintenance guidelines

24. Design for Failure How DFF fits into PD Process • You can identify potential design for failure opportunities through multiple ways: • Upfront Design • Customer wants and needs (surveys) • Focus Groups • Competitive product analysis • Aftermarket product analysis • Review product requirements and restrictions • Review assembly, serviceability and maintenance requirements

25. Design for Failure How DFF fits into PD Process • You can identify potential design for failure opportunities through multiple ways: • Design Phase • Analyzing overall system architecture • Conducting DFMEA’s on product or system • Simulating critical system interactions and interfaces • CAE modeling and analysis should be done for FEA, Electrical fuse blow, Worst Case Circuit Analysis, voltage drop and resistance change over time/temp are commonly done to predict and manage failures

26. Design for Failure How DFF fits into PD Process • You can identify potential design for failure opportunities through multiple ways: • Design and Release • Analyzing a component/system that has failed • The Product Design and Development team reviews the data and decides on the overall system architecture.

27. Design for Failure • Introduction to Design for Failure (DFF) • System Engineering V-Model and DFF • Heuristics • How DFF fits into PD Process • Situation to implement DFF • Examples • Summary

28. Design for Failure Situations to implement DFF • The main purpose of designing for failure is the prevention of injury or harm to a system, component or person in the event of a potential system or component failure (either catastrophic or minor). • Design for failure also used to prevent costly repair. The fusible component should be the least expensive to repair (ex: half-shafts). • These systems were developed to meet thiscriteria: • Air Bag Deployment System • Electrical Circuit Protection • Whiplash Protection Seating System (WHIPS)

29. Design for Failure Situations to implement DFF • Collapsible Steering Column • Windshield Breakage • Run “Flat” Tire • Paper Shredder

30. Design for Failure Concepts in Planning for Failure • Single Point Failure – Example: If system operations depend on knowing the time and there is only one watch, it becomes a single point failure mechanism. (Smead) • Redundant Systems – Example: Having 2 watches there is a backup device to tell time. However, you must have a way to resolve inconsistencies between the two watches to determine the correct time. (Smead) • Failsafe – “describes a device which if (or when) it fails, fails in a way that will cause no harm or at least a minimum of harm to other devices or danger to personnel.” (Wikipedia) • Failover / Switchover – a device that takes over for a failed mechanism only after the point of failure (Smead) • Ping-pong – devices that take turns operating, so as not to get overloaded, (beware of inconsistencies) (Smead)

31. Design for Failure “Fail-safe” mechanism failure examples • Therac 25 – Computerized radiation therapy machine(Leveson) • 1985-87 Injuries and deaths from radiation overexposure • Model had replaced several mechanical interlocks for safety with software algorithms. • Operators were able to retry administering doses after a dose-rate malfunction was indicated incorrectly by the software. • A safety analysis of the device in 1983 by manufacturer excluded software in the fault tree analysis. • Christus St. Joseph Hospital – Elevator Decapitation(Greene) • August 2003, Surgical Intern, Hitoshi Nikaidoh pinned in elevator doors while closing, decapitated when elevator raised • Nikaidoh had expected the elevator doors to retract when an obstacle (his body) was encountered but they did not. Lesson: Fail safe devices, poke-yokes and safety mechanisms must be fully tested for proper designed function. Don’t assume they work properly, or will continue to work properly over time.

32. Design for Failure • Introduction to Design for Failure (DFF) • System Engineering V-Model and DFF • Heuristics • How DFF fits into PD Process • Examples • Summary

33. Airbag Deployment System

34. How does it relate to DFF? • The air bag system is designed to deploy in the event of an accident (failure of a system or component). • Consistent deployment is vital in airbag designs. This means consistent failure of components that contain airbags is vital.

35. How does it work? • Internal seam in steering wheel covers allows for uniform failure in order for airbag to inflate in a consistent time and manner. • Seats and Headliners • Some designs have a panel that opens like a door in order to have controlled deployment of the seat side air bags. • Headliners typically have a weak point in the design that will break during the deployment.

36. Electrical Circuit Protection

37. How does it relate to DFF? • The electrical circuit system is designed for … • One Time Applications • Once failed the component cannot be reused. • Bolt-In Fuse • J-Case Fuses • Maxi/Mini Fuses

38. How does it work? • The circuit protection system is designed to fail when the conditions (listed below) are over exerted. • Following parameters are part of circuit protection selection. • Ambient Temperature • Breaking Capacity • Operating Voltages in Volts • Operating Current in Amperes • Required Failure Time • Re-settable or One-Time

39. Resettable Breakers • Once the component fails, it can be manually reset and used again. Some reset themselves after failed condition is stopped. • Blade Design • 120/240V AC Single pole breaker (typically used in residential wiring) • High Speed Fuse Applications • Used with Allen-Bradley Controllers and Drivers. • Manufacturing Equipment Application

40. Volvo Whiplash Protection Seating System (Whips)

41. How does it relate to DFF? • The WHIPS system, unique to Volvo, is designed to provide markedly better protection from neck and back injuries in the event of a rear impact How does it work? • In the event of a rear impact, the WHIPS seat responds immediately • The seatback/headrest assembly moves back and then tilts down, absorbing the impact • In laboratory tests acceleration forces on the neck are reduced by up to 50%. • Under normal condition this would be a failure of the seat system

42. Collapsible Steering Column NASCAR Steering Column

43. How does it relate to DFF? • Volvo has designed a steering column that collapses down and away from the driver during a severe crash (system failure). How does it work? • Upon impact, the steering column structure fails in order to protect the customer.

44. Windshield Breakage

45. How does it relate to DFF? • The windshield is designed to provide a clear and undistorted view to the driver and passenger AND minimize danger in the event of a collision. • The windshield in a vehicle is designed to stay in place upon impact. The glass will not shatter into a lot of small pieces. This protects the vehicle occupants from serious injury. • The safest place to be during a car accident is in the car. Your windshield is an important barrier that keeps you in the car. A cracked windshield can fail during a collision or rollover, allowing you or your passenger to be ejected. A passenger ejected from a car or truck is much more likely to experience a serious injury or death.

46. How does it relate to DFF? • An automobile's windshield is designed to prevent the roof from crushing you in a rollover accident. A windshield can be significantly weakened by cracks and may fail to support the roof if the car flips over, causing severe injury or death to occupants.

47. How does it work? • Windshield glass is made by fabricating ordinary glass (flat) into high-grade shaped and tempered glass. • Two primary types of safety glass: • Laminated (Front Windshields) • Tempered (Side/Rear Windshields) • Many people don't realize that front-seat passenger airbags deploy against the windshield. • In the event of a front-end collision, a cracked windshield can fail, allowing passengers who aren't seat-belted properly to be ejected from the vehicle through the windshield.

48. Run “Flat” Tire

49. How does it relate to DFF? • The “run flat tire” is a system that is designed to allow the driver to continue to drive their vehicle in the event of a tire blowout (product failure). How does it work? • When the tire loses pressure, it rests on a support ring attached to the wheel. • Majority of the run-flat capability is on the wheel versus the tire. The wheel does not “wear out” whereas, the tire does wear out and require replacement. • Benefit of Run Flat Tire • Eliminate the need for spare tire – reduce the weight of vehicle – increase fuel efficiency • Allow more luggage space by eliminating the spare tire • Increase driver security and confidence in their vehicles • Promise better ride quality because their sidewall's stiffness can be equivalent to today's standard tires versus the other technologies that are on the market (self sealing and self supporting)

50. Ford AWD System Heat Management Software PTU Includes: Power transfer Unit (PTU), Rear Drive Unit (RDU) AWD Coupling AWD Coupling (In RDU)