MPD 575
Design for Failure
Jonathan Weaver
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Developed By:
Cohort Team 3:
Cathy Campbell
Brandon Johnson
Robbin McDaniel
Britt Scott
Updates by Anita Bersie
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Design for Failure
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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
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Design for Failure
Design:
– Creative process in the Arts, Sciences and
Technologies.
– There are many design heuristics that are derived
from rules, relationships and experiences.
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Design for Failure
Failure:
The many definitions of failure are:
• System Failure takes place when load exceeds
capacity by an unacceptable amount
• Different types of Failures (highly dependent on
the individual):
– Failures which cause unacceptable damage
(important or catastrophic)
– Failures which cause damage of little or no
importance.
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Design for Failure
Failure, cont’d:
– Failure should be qualified and quantified if possible.
– 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.
• The cause of the conditions are uncontrollable by
the engineers but the failure under these conditions
can be controlled.
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Design for Failure
Team’s definition of DFF:
“A system or component designed to fail under certain
conditions or circumstances”
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Design for Failure
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•
•
•
•
•
•
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
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Design for Failure
The System Engineering V-Model has three
phases:
1. Design the Product or Component
2. Optimize the Design
3. Validate the Design
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Design for Failure
Key “DFF” Procedures in relation to the System
Engineering V-Model
• Design the Product or Component
– Understand the System Architecture (design)
– Determine the acceptable failure criteria or
requirements
– Conduct a DFMEA on the system or component
– Rank severity of failures
– Implement actions taken to reduce severity of
failures identified as critical and unavoidable
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Design for Failure
Key “DFF” Procedures in relation to the System
Engineering V-Model
• Optimize the Design
– Evaluate design actions to reduce failure
severities of unavoidable failures with minimal
impact on: cost, weight and system function
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Design for Failure
Key “DFF” Procedures in relation to the System
Engineering V-Model
• Validate the Design
– Test System for Failure
• Analyzing failure types
• Failure detection
• Verify severity of failure
– Verify that the design under the identified failures
meets customer specification by using modeling
and prototypes
– Retest the system
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Design for Failure
Definition of Key DFF Procedures:
• System Architecture is defined as the art and science of
creating and building complex systems. That part of
systems development most concerned with scoping,
structuring, and certification
• Failure Mode Effect Analysis (FMEA) is defined as
systematized 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, and
3) document the process
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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.
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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.
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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
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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)
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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)
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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
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Design for Failure
How DFF fits into PD Process
1. Gather raw data from the customers
2. Interpret the data in terms of customers needs.
3. Organize and establish the importance
4. Establish target specifications
5. Identify any potential products that require safe
failure modes
6. Determine the strategy
7. Establish warranty guidelines
8. Include the failure strategy in overall system
architecture – boundaries for failure
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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
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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
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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 DFMEAs on product or system
• Simulating critical system interactions and
interfaces
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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.
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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
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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).
• The following systems were developed to meet the
above criteria:
– Air Bag Deployment System
– Electrical Circuit Protection
– Whiplash Protection Seating System (WHIPS)
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Design for Failure
Situations to implement DFF
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Collapsible Steering Column
Windshield Breakage
Run “Flat” Tire
Paper Shredder
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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 back-up 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, (also beware of inconsistencies) (Smead) 28
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.
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Design for Failure
•
•
•
•
•
•
Introduction to Design for Failure (DFF)
System Engineering V-Model and DFF
Heuristics
How DFF fits into PD Process
Examples
Summary
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Airbag Deployment System
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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.
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How does it work?
• Internal seam in steering wheel
covers allows for uniform failure
in order for airbag to inflate in
an 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.
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Electrical Circuit Protection
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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
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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
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• Re-Settable Breakers
– Once the component fails,
it can be manually reset
and used again. Some
reset themselves after
failed condition is stopped.
• Blade Design
• 120240V AC Single
pole breaker (typically
used in residential
wiring)
• High Speed Fuse Applications
– Used with Allen-Bradley
Controllers and Drivers.
– Manufacturing Equipment
Application
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Volvo Whiplash Protection
Seating System (Whips)
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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.
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Collapsible Steering Column
NASCAR Steering Column
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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.
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Windshield Breakage
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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 roll over, 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.
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How does it relate to DFF?
• An automobile's windshield is
designed to prevent the roof
from crushing you in a roll over
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.
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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)
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•
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.
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Run “Flat” Tire
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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)
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Design for Failure
• Paper Shredder
(Jam Mechanism)
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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.
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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
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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.
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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 subcomponent that is part of the product system design
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Design for Failure
References
• 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 Edward53
th
References
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•
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.
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References (Cont)
• Smead, David. “Vessel Networking #2.” On-line
posting. 8 May, 2007. Available:
http://www.amplepower.com/dave_blog/2/vessel_networ
king_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.
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QUESTIONS
????
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Design for Failure
Thank You
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