MPD 575Design for Failure

Developed By:Cohort Team 3:Cathy Campbell

Brandon JohnsonRobbin McDaniel

Britt Scott

Updates by Anita Bersie, Joe Torres, Beatriz Dhruna, John Haddock, Mac

Lunn

20140426 MPD575 Weaver

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

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

Design for FailureDefinitions 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 effects2) identify actions to eliminate or reduce the chance of the potential failure occurring3) document the process

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.

• ApproachDesign 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.

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.

Design for Failure

Team’s definition of DFF:

“A system or component designed to fail under certain conditions or circumstances”

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

Design for Failure

System design has three phases:

1. Design the Product or Component

2. Optimize the Design

3. Validate the Design

Design for FailureDesign 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.

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.

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.

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

Conducting a DFMEA

1. Review the Design and Interfaces

2. Brainstorm potential failure modes – Review existing documentation and data for clues

3. List potential effects of failure

4. 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.

5. Assign Occurrence rankings – How frequently is the cause of failure likely to occur?

6. Assign Detection rankings – What are the chances that the failure will be detected prior to the customer finding it?

7. Calculate the RPN – Severity x Occurrence x Detection

8. Develop the action plan

9. Take Action

10. Calculate the resulting RPN

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

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.

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

Design for Failure

HeuristicsP = 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)

Design for FailureHeuristics (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)

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

Design for Failure

How DFF fits into PD Process1. Gather raw data from the customers2. Interpret the data in terms of customers needs.3. Organize and establish the importance4. Establish target specifications5. Identify any potential products that require safe

failure modes6. Determine the strategy7. Establish warranty guidelines 8. Include the failure strategy in overall system

architecture – boundaries for failure

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

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

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

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.

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

Design for FailureSituations 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 this criteria:– Air Bag Deployment System– Electrical Circuit Protection– Whiplash Protection Seating System (WHIPS)

Design for Failure

Situations to implement DFF– Collapsible Steering Column– Windshield Breakage– Run “Flat” Tire– Paper Shredder

Design for FailureConcepts 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)

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.

Design for Failure

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

Airbag Deployment System

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.

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.

Electrical Circuit Protection

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

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

• 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

Volvo Whiplash Protection Seating System (Whips)

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

Collapsible Steering Column

NASCAR Steering Column

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.

Windshield Breakage

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.

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.

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.

Run “Flat” Tire

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)

Ford AWD System Heat Management Software

Includes: Power transfer Unit (PTU),

Rear Drive Unit (RDU) AWD Coupling

PTU

AWD Coupling(In RDU)

How does it relate to DFF?– The AWD software prevents permanent sump oil and clutch plate damage by predicting

temperatures via modeling techniques. It then takes action by adjusting system behavior to either prevent or reduce further temperature rise. Actions are unique to which component is suspect.

How does it work?– If the PTU sump approaches 130 Deg C at a minimum rate, the software reduces the

assumed torque level to the rear axle in order to affect the temperature behavior. If temperature rise remains and exceeds 145 Deg C (The synthetic lube limit), AWD is disabled until the temperature drops below 130 Deg C again, or 5 minutes have expired. Whichever comes last. Goal is to provide as much function to the customer as possible before disabling.

– If the AWD clutch plate temperature exceeds 210 Deg C, this is due to excess front to rear slip in severe sand or deep snow conditions. The software responds by sending 3x the normal duty cycle to the AWD coupling. This essentially “locks” the coupling and prevents further heat rise. However, if the lock mode cannot prevent slip and the coupling continues to rise past 240 Deg C, The AWD system is disabled . This prevents permanent damage to the clutch plates

– If the RDU sump exceeds a limit of 120 Deg C (natural lube), the AWD software performs actions similar to that seen on the PTU. In this case, locking up the coupling would typically make the RDU sump situation worse. Therefore, reduced torque is warranted.

– The entire system is a balance of tradeoffs. I.E. if the PTU torque level is reduced, this causes higher risk of clutch plate temperature rise. If the clutch plates are “locked”, this causes higher risk of PTU temperature rise. A balancing act, indeed, requiring good usage of systems engineering skills.

– Benefit of Designing for temperature failures• With modern AWD systems, overheating is more a matter of “when” vs. “if” it happens.• Robust software balances performance with durability life to provide customer with best value• Part Failures result in very high warranty or customer costs (Ex. RDU replacement = $3,000)• Damage often seen after warranty is expired, resulting in dissatisfaction

Ford Thermal Management

Heat Shield Examples

Mitigation Techniques

Exhaust mounted Shields

Stamped Shields

Fuel Tank Shield Air Scoop and Deflectors

Thermal Sleeving

How does it relate to DFF?– The Thermal Management techniques are designed in place with the expectation of failure

in the product life cycle.

How does it work?– The Heat Management engineer designs mitigation techniques into the product with the

expectation that a failure will take place. The failures considered are misfire and exhaust failure.

– Although in majority of the cases the powertrain controls software would recognize that a misfire or an exhaust failure has occurred and will management the failure according, testing is conducted with these features turned off.

– Testing is defined as endurance• No Ignition of Vehicle or Components• No Smoke or Noxious Fumes• No Loss of Fluids• No Failure of Severity 8,9,10 (FMEA)\• No System degradation that affects vehicle safe

– Benefit of Designing for misfire and exhaust failures• Allows engineer to evaluate Component Maximum Design Temperatures listed in SDS to Ensure

Thermal Robustness

Ford Thermal Management

Design for Failure

• Paper Shredder (Jam Mechanism)

Design for Failure

Paper Shredder (Jam Mechanism)How does it relate to DFF?• The paper shredder is designed to shred paper. If too many sheets

or a non-paper object (metal, thick plastic) are fed through it the failure mode is to jam or stop working before damaging the product.

How does it work?• There are several shredder designs available (electrical or battery

operated) to accept different quantities ( 1 thru 140 sheets) of paper. The paper is then fed thru the shredder opening.

• If the quantity or thickness is too great the shredder jams.• If a non-paper object is placed in the shredder it jams.• Once the extra sheets or object is removed, the shredder reset

button can be activated.

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• Case Study• Examples• Summary

Design for Failure

Summary• Incorporate the DFF procedures into each design• Define useful life of product and its failures• Challenge engineering to develop customer satisfaction

criteria for all types of uses/ misuses (additional failures)• Develop products or processes that meet the failure

mode and is robust against different sources of variation• Address new technology or existing technology in new

environments against the failure modes• Design for failure may prevent more damage by making

the system inoperable.

Design for Failure

Summary• Gain an understanding of a system’s failure sensitivity• Meet the global challenge of incorporating product failure

modes on all components or systems• Look at the big picture, address a component or sub-

component that is part of the product system design

Reference• The Art of System Architecting, M. Maier &

Rechtin, 2nd edition, CRC Press, 2000• Systems Architecting of Organizations, CRC

Press, 2000• Product Design and Development, Karl T. Ulrich

and Steven Eppinger, 2nd edition • Mechanics of Materials, A. Higdon, E. Ohlsen,

W. Stiles, J. Weese, W. Riley; John Wiley & Sons, Inc, 4th Edition, 1985

• Mechanical Engineering Design, Joseph Edward Shigley, Charles Mischke; McGraw-Hill, Inc, 5th Edition, 1989

References

• www.fpds.ford.com/fpds2k/index.html• www.ford.com……• www.destroyit-shredders.com• www.bestbuy.com• www.helmets.org

• http://www.be.ford.com/safety/training/general%20airbags/airbag101/links.htm

• www.ask.com/main/metaAnswer.

References (Cont)• Smead, David. “Vessel Networking #2.” On-line posting.

8 May, 2007. Available: http://www.amplepower.com/dave_blog/2/vessel_networking_2.pdf

• Greene M.D., Alan. “A Tragic Lesson.” On-line posting. 20 Aug, 2003. Available: http://www.drgreene/com/21_1660.html

• “Failsafe.” Wikipedia [On-line]. 26 Oct, 2007. Available: http://en.wikipedia.org/wiki/Failsafe

• Leveson, Nancy & Clark Turner. “An Investigation of the Therac-25 Accidents.” IEEE Computer, Vol. 26, No. 7, July 1993, pp. 18-41.