EMA 630 Viscoelastic Solids
Case studies and applications
Baby head deformation. Creep and recovery.
head 0,
head 1,
head 2,
head 3,
head 4,
head 5
head 6
full article
Discussion: Head deformation in response to prolonged force is known.
Discuss the baby's perspective and the parents' perspective in the context of ethics. Discuss the role of creep and recovery.
Space shuttle explosion. Recovery; polymer behavior.
Story, Wikipedia
Feynman video
Discussion: glass transition of polymers; estimates of risk (one in a million vs. one in a hundred); meaning of factor of safety; claims for the shuttle, routine, safe, cheap space travel.
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled",
Richard Feynman. Reference: Feynman's analysis of the space shuttle Challenger explosion, described in the book Feynman, R., "What do you care what other people think".
Einstein quote
"Concern for man himself and his fate must always form the chief interest of all technical endeavor. Never forget this in the midst of your diagrams and equations."
link 1
link 2
Big dig tunnel disaster, Boston. Nonlinear creep.
Story, NYT
Story, CBS indictment
Wikipedia error known
Discussion: creep of polymers; creep failure; concern for quality.
Vajont dam; Vajont slide. Nonlinear creep.
Wikipedia risk known
Discussion: creep failure; concern for quality.
SF's Millennium Tower tilt
Trench stability. Creep failure.
"The stand-up time for a trench is the time that elapses from the time the trench is dug until the trench walls start collapsing".
Discussion: time dependence of materials; ethics.
Hand strength exerciser for rehabilitation after injury. Rate dependence.
Exercise putty
Discussion: material viscoelasticity; good will in design.
Jet engine turbine blades. Creep at high temperature.
Discussion: experiment, constitutive modeling, choice of material. What causes creep in metals at high temperature?
speed
Relaxation of screws in computer disk drives and in engines. Relaxation at "high" temperature.
Discussion: experiment, constitutive modeling, choice of material. Is it really relaxation?
Vibration damping.
Structural materials such as steel and aluminum alloys have low damping. High damping polymer materials are too compliant for use in structures. To achieve practical high damping, a layered design is used. The benefit is to reduce noise that is annoying or even can damage the ear. The benefit at lower frequency is to reduce annoying vibration that may also be harmful to humans or cause equipment to fail.
Tacoma Narrows Bridge
link Wikipedia
link video
Discussion: can the effective damping be negative? What about positive definiteness? Coupled fields; smart materials and structures. Modern bridges are designed with sufficient structural rigidity; they are designed to damp vibrations. Some bridges are provided with slots in the middle of the deck to alleviate differences in air pressure above and below the road. See, e.g. Nov. 2015 Physics Today on the Tacoma Narrows Bridge.
Footbridge motion
When the London Millennium footbridge was opened in June 2000, it swayed alarmingly. It was closed for two years out of concern for safety.
Discussion. When analyzing a system, what are the system boundaries?
Fluids: engine sludge can destroy a car engine quickly. Motor oil can turn to sludge in some cars, particularly if short trips are taken in cold weather.
Engines to avoid. Why sludge.
Consumer reports
Discussion: non-Newtonian fluids; physical aging of fluids; ethics; honesty.
Rolling resistance. Tires.
Discussion. Why do tires become warmer after driving? How does rolling resistance relate to tan delta? Why? Why does rolling resistance decrease when the tire is given more air pressure? Why not increase air pressure to the maximum that the tire can endure? How might a layered structure improve performance?
Vibration isolation.
Protection of humans or of devices which humans use; compliant supports. Seat cushions. Glove liners.
Impact isolation.
Protection of humans or of devices which humans use; compliant layers. Shoe insoles. Bumpers.
Rebound resilience.
Sports. Squash. Baseball
Satellite stability.
Minimum energy for a spinning object.
Frequency standards; time keeping.
Sharpness of resonant response. Power required to maintain resonance.
Case study: Concern for quality. Therac radiation device.
link
Discussion. Engineering ethics. Redundancy. Concept of fail-safe.
Case study: Concern for quality. L. A. train wreck killing 25 people and injuring 135. Risk known.
The engineer of a Metrolink train in the Los Angeles area failed to stop at a red signal and crashed head on into another train, killing 25 people. The engineer was text messaging with a teenager at the time. Some 135 people were injured in the crash, more than 40 of them critically.
Story, Fox news
Story, Reuters
Case study: Concern for quality. Spain train wreck: 79 dead and at least 66 serious injuries, some catastrophic. Risk known.
Case studies: Multitasking does not work; it can have disastrous consequences.