design failure
DESCRIPTION
Design Failure. When Does a Design Fail?. A failed design is a design process which one does not achieve the specified design goals. In this class, failure could be project cancellation due to nonperformance or no support for next year’s project. Conventional Types of Design Failure. - PowerPoint PPT PresentationTRANSCRIPT
University of Connecticut MECHANICAL ENGINEERING
Design Failure
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University of Connecticut MECHANICAL ENGINEERING
When Does a Design Fail?
A failed design is a design process which one does not achieve the specified design goals.
In this class, failure could be project cancellation due to nonperformance or no support for next year’s project
University of Connecticut MECHANICAL ENGINEERING
Conventional Types of Design Failure
1. It doesn’t work!
2. It would work, but ……..!
3. It works, but no one wants it!
4. Ooops [we’ll see what this means]
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It doesn’t work [broad definition]!
Cannot find a design solution that meetsperformance, cost, time, etc. specifications - even after compromises.
Examples: Fusion reactor for power - too costly, inefficientGeared turbofanElectric Car - performance/cost not acceptable
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It would work, but …..!
All the theory, analysis, experiment and simulation says it should work, but it doesn’t.
Example: F-102 delta wing pursuit plane [We will see about this shortly].What are your teams doing to ensure success?
Theory: _______________ Analysis: ______________ Experiment: ____________ Simulation: _____________
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It works but no one wants it!
The operation was a success but the patient died. Examples:
Ford Edsel - great car, freak designSony Betamax - people wanted VHSDEC PC’s - incompatible floppy
Not normally an issue for your teams, but make sure you are doing what sponsor wants / needs
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Oops!
It works, but some unanticipated condition or reason causes it to
fail.
Examples: Challenger Disaster - “O” rings failed below freezing temperatureCivic Center Roof - overloadedMianus River Bridge - mechanical failure
How do you minimize your risks?
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Design Failure Categories
Catastrophic: - Serious damage to life, property;
- Serious financial loss; etc.
Soft: - Design goals not met but nobody hurt,
- Missed opportunity
Repercussions:- No UCONN support for next year
- No job offers to graduates
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Failure Mechanisms
1. Financial 2. Performance
3. Physical 4. Process
5. People
Let’s now look at each of the above failure modes
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Failure Mechanisms
1. Financial
- Design cost too high
- Production cost too high
- Marketing unsuccessfulloss of market advantage
- Inadequate service organization
- Liabilities
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Failure Mechanisms
2. Performance
- Fails under certain environmental conditions.
- Fails under certain operating conditions
- Fails to achieve full performance specs
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Failure Mechanisms
3. Physical
- Mechanical - overstress, fracture, fatigue, over- heating, lubrication, corrosion, tolerances
- Electrical - overheating, burnout, bad solder/ connector, tolerances, timing
deterioration
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Failure Mechanisms
3. Physical [cont’d]
- Hardware/Software Programming bug, timing problem,
interfacing problem, too slow, not enough memory, glitches
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Failure Mechanisms
4. ProcessDesign is OK, but implementation a problem
- Ford Taurus ignition switch- Firestone ATX tires (see later)- K.C. Hyatt (see later)
5. PeopleDesign is OK, but people can be a problem
- skill level of workers (Firestone Decatur plant)- supervision of workers (PW TF30 for F111)- interest level of workers
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Failure Mechanisms
Now let’s consider some examples of
design failures that are both infamous and
catastrophic
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Design Failure: Firestone ATX Tires
Who was at fault, Ford or Firestone? ATX tires used on trucks never had failure modes Statistically greater failure of left rear tires
Physical- shoulder pockets (for traction in mud and snow) cut too deep,
leaving too little rubber on edge- shoulder pockets cut at right angles to tread increasing strain on
shoulder
Process or People - Manufacturing standards at Decatur plant were inconsistent- Decatur plant used too much lubricant to keep rubber compounds
from sticking together during manufacturing. Belts from this plant did not stick to each other as well as in other plants.
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Design Failure: YF102
YF-102
• Convair [Gen. Dyn.] delta-winged fighter
• Unable to fly supersonically, i.e. M < 1
• Problem diagnosed as limited by physical principle not mechanical shortcoming
• Area rule (Whitcomb, NACA)• blockage of wings causes excessive drag rise
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Design Failure: YF102
YF-102
YF-102ASolution is to reduce flow blockage
• Coke bottle fuselage design
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Design Failure: DC10 Cargo Door
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Design Failure: DC10 Cargo Door
All commercial aircraft are pressurized while flyingOutside air is at low pressure compared to cabinInward opening door plug tight against door frameCargo door open outward so as not to lose interior cargo storage spaceDC10 door locking procedure [baggage handler]Pull down top-hinged door and shut itSwing down lever on outside or doorPress and hold button operating electric motorPut ear to fuselage until hear click, then hold for 7 more
seconds till motor stops
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Design Failure: DC10 Cargo Door
DC10 flight on June 12, 1972 from Detroit to Buffalo
DC10 baggage handler has difficulty closing door, but forces lock which gives false signal of locking
After takeoff, cargo door blows out sucking out rear galley and damaging hydraulic cables and cables to tail
Pilot deviates from accepted procedures and successfully landed plane; design changes recommended
Turkish Airlines inspection paperwork stamped with quality control approval [indicating cargo door repaired]; plane crashed in 1974 due to cargo door failure, killing 346.
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Design Failure: K.C. Hyatt Atrium
Background
• Plush hotel complex with atrium inter connecting 3 buildings• 2 / 1 pedestrian walkways for the 2-4 / 1 floors • At evening tea dance in atrium (1981) with people dancing on walkways; 2-4 floor walkways collapsed
• Worst structural disaster in U.S. History• 114 dead, 200 injured
• Owner (D. Hall) settled more than 90% of claims out of court as a sense of duty and civic responsibility
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Design Failure: K.C. Hyatt Atrium
Observation: failure site noted at 4th floor box beam hanger on walkway Walkway sliding (bearing) support chosen to allow beam to expand /
contract with temperature changes
Brainstorming of Failure Causes People dancing on walkways sets up a resonance Quality of material used in construction Construction crew skill level On-site contractor (as-built) modification of final design
Design changes approved by architects and structural engineers
As built 4th floor support takes twice the designed load
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Design Failure: K.C. Hyatt Atrium
Box Beam Hanger-as Built Box Beam Hanger-as Designed
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Design Failure: K.C. Hyatt Atrium
Actual dead load (weight of all components) of walkway was 8% greater than designed dead loadLive load (required by K.C code was 72,000 lbs/walkway), but with 63 people on 2 walkways, actual live load = 63 (150 lbs) = 9450 lbs << 72,000 lbsLoad per 6 supports therefore was 72,000 * 2 / 6 = 24,000
Notes do not say what design should be able to take
Principal manager and project manager fro m structural firm had
Missouri license revoked for not calculating whether support would work.
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Design Failure: Boston Hancock Building
Background• 60 story floor-to ceiling reflective glass panels• Glass panels started blowing out from the beginning of construction (1973). At times more than 1/3 of panels were out.• Cause not certain due to legal agreement of “nondisclosure in perpetuity”• Design satisfied all governing codes• Some information gleaned from construction grapevine
Window design• Double-glazed, doubled pane panels• Lead spacer at edges to separate panels• Design allowed for view of continuous glass
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Design Failure: Boston Hancock Building
Brainstorming
• Large wind storm correlated to panel blowout Lateral deflection of structure due to wind effect not verified in tests• Twisting motion (short direction) observed by tenants (had to be damped out)
• 600 tons of lead dampers added near roof
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Design Failure: Boston Hancock Building
Failure Cause Analysis
• Glass panels were correctly installed• Thermal stress cycles induced by compression / expansion of air between panes • Most panes cracks found in outer panes first• Lead solder overconstrains glass causing premature fatigue
Replace all 10,344 panels with single pane glass
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Guarding Against Failure
Organizational
Management Plan
Financial Plan
Marketing Plan
Engineering
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Guarding Against Failure
Engineering
Modeling / Simulation
Design Review [CDR, Tiger Teams]
Prototyping
Testing
Maintenance Plan
Failsafe Design - Redundancy
Documentation
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What are your teams doing to ensure success?
Theory: _______________ Analysis: ______________ Experiment: ____________ Simulation: _____________
University of Connecticut MECHANICAL ENGINEERING
What are your teams doing to ensure success?
Finally remember to document your failures for you and others to learn from….
But if someone has to be blamed for a project failure, blame your advisor.