MSE 200A Fall, 2008

MSE 200A: Survey of Materials Science

•  Instructor: J. W. Morris Jr. 228 Hearst Mining Bldg. Tel: 642-3815 E-M: jwmorris@berkeley.edu Office hours: 10-11 am Monday, 11am-12pm Wed.

•  Web site: –  http://www.mse.berkeley.edu/groups/morris/courses.html

•  TA: Liz Zimmerman

MSE 200A Fall, 2008

MSE 200A: Survey of Materials Science

•  Text: Bound lecture notes will be available

•  Examinations (open book): –  Midterm –  Final as scheduled

•  Homework: –  Approximately 10 sets

MSE 200A Fall, 2008

MSE 200A: Survey of Materials Science

•  Survey course that covers the field of Materials Science –  “One mile wide, one inch deep” –  Materials are treated in many courses; what is different here?

•  The scope of Materials Science –  What the properties of materials are, but also –  Why they are what they are

•  What is a “material”, anyway? –  How they can be modified and controlled

MSE 200A Fall, 2008

•  The field can be summarized in two sentences: –  Properties <= composition + microstructure –  Microstructure <= composition + processing

•  Composition = kind and fraction of atoms present

•  Microstructure = How those atoms are arranged –  Microstructure is not only essential to understanding properties –  It is often much more important than composition –  Example: endovascular stents from 316L stainless (Fe-Cr-Ni-Mo)

•  Self-expanding (hard in as-drawn condition) •  Balloon-expanded (soft in annealed condition)

The Essence of Materials Science

MSE 200A Fall, 2008

Endovascular Stents: Microstructure controls strength of 316L

•  Self expanding –  Hardened 316L (drawn) –  Compress, insert –  Relaxes to original d

•  Balloon expandable –  Soft 316L (annealed) –  Compress to small d –  Put on balloon, insert –  Blow up balloon to original d

MSE 200A Fall, 2008

Outline of the Course

•  Composition = atoms or molecules present

•  Microstructure = location of atoms or molecules –  How can we locate 1023 atoms? –  Use reference states:

•  Crystal (periodic distribution) + defects •  Glass (random distribution) + defects

•  Properties –  Thermochemical (response to heat or environment) –  Electromagnetic (response to electromagnetic fields) –  Mechanical (response to mechanical forces)

MSE 200A Fall, 2008

Microstructure

•  Crystalline solids –  Bonding

•  Inherent properties: electrical, mechanical –  Nature of crystal structure –  Common structures (mainly cubic) –  Defects in crystals and their consequences

•  Point defects: diffusion, electrical properties •  Line defects (dislocations): plastic deformation •  Surfaces (boundaries, faults): environmental interactions, embrittlement •  Volume (voids, precipitates): strength

•  Amorphous solids (glasses) •  Macromolecular solids

–  Polymers –  Silicates –  Fibers –  Membranes

MSE 200A Fall, 2008

Thermochemical Properties

•  Thermodynamics –  Conditions of equilibrium and stabilty –  Phase diagrams

•  Kinetics –  Deviation from local equilibrium: heat conduction, diffusion –  Deviation from global equilibrium: phase transfromations

•  Surface effects –  Interfacial interactions, wetting

•  Environmental effects –  Oxidation and corrosion

MSE 200A Fall, 2008

Electromagnetic Properties

•  Electrical properties –  Metals –  Semiconductors

•  Semiconductor junctions •  Manufacture and packaging

–  Dielectrics

•  Optical properties –  Waves: refraction, reflection, transmission –  Photons: photoconductors, photodetectors, lasers

•  Magnetic properties –  Ferromagnetism

•  Superconductors

MSE 200A Fall, 2008

Mechanical Properties

•  Elastic properties –  composites

•  Yield strength and plasticity –  Strengthening mechanisms

•  Solute, dislocation, precipitate and grain hardening –  Plastic deformation

•  Work hardening •  Plastic instability and fracture

–  Temperature: softening, creep

•  Fracture –  Fracture toughness

•  Mechanisms of fracture •  Controlling toughness

–  Crack growth mechanisms •  Fatigue •  Stress corrosion cracking, hydrogen embrittlement

MSE 200A Fall, 2008

Why do you care?

•  Necessity –  Everything is made out of something –  Materials selection is critical to design and performance –  “Best” selection is not always “best” material

•  Ambition –  New materials => new opportunities –  But must understand opportunities to exploit them

•  Ex: transistor to integrated circuit •  Ex: laser •  Ex: high-Tc superconductors

•  Fear –  Most failures are materials failures –  Poor materials selection –  Inappropriate use –  Failure to anticipate problems

MSE 200A Fall, 2008

Bronze or Iron?

•  At the start of the “iron age” –  Bronze was stronger –  Bronze was tougher

•  Bronze was preferred for armor

•  So why the rapid shift to iron? –  Iron was cheaper, more available –  Bronze age armies of 1,500 (Egypt) –  Iron age armies of 20,000 (Assyria)

•  History is full of examples: –  Cheaper and easier is better

•  Muskets vs. compound bows •  Model T vs. Mercedes •  Silicon vs. GaAs •  Aluminum vs. plastic composites

Bronze sword (Greek)

Iron sword (Roman)

MSE 200A Fall, 2008

Why do you care?

•  Necessity –  Everything is made out of something –  Materials selection is critical to design and performance –  “Best” selection is not always “best” material

•  Ambition –  New materials => new opportunities –  But must understand opportunities to exploit them

•  Ex: transistor to integrated circuit •  Ex: laser •  Ex: high-Tc superconductors

•  Fear –  Most failures are materials failures –  Poor materials selection –  Inappropriate use –  Failure to anticipate problems

MSE 200A Fall, 2008

Lasers

•  OK, we got rayguns. What are they good for? –  Pulverizing aliens –  Subdividing James Bond –  Transmitting energy –  Ideas, anyone?

MSE 200A Fall, 2008

High-Tc Superconductors

•  The Woodstock of physics –  March APS, 1987

•  High-Tc is the best idea since sliced white bread –  It isn’t? –  Was sliced white bread such a good idea, anyway? –  Was Woodstock?

MSE 200A Fall, 2008

Why do you care?

•  Necessity –  Everything is made out of something –  Materials selection is critical to design and performance –  “Best” selection is not always “best” material

•  Ambition –  New materials => new opportunities –  But must understand opportunities to exploit them

•  Ex: transistor to integrated circuit •  Ex: laser •  Ex: high-Tc superconductors

•  Fear –  Most failures are materials failures –  Poor materials selection –  Inappropriate use –  Failure to anticipate problems

MSE 200A Fall, 2008

Bridge Failures

•  Bridge collapse –  Increasing problem –  Fear and fatality

•  Causes –  Structural deterioration –  Rebar corrosion is common

MSE 200A Fall, 2008

Alaska Flight 261

Porto Vallerto - San Francisco Crashed near Los Angeles

January 31, 2000

MSE 200A Fall, 2008

Alasks 261 - Flight path to accident

MSE 200A Fall, 2008

Alaska 261 - event sequence

•  Take-off –  Autopilot turns itself off –  Horizontal stabilizer locks

•  Straight and level flight to near LA (~ 2 hrs.) –  Autopilot spontaneously re-engages

•  Attempt to free horizontal stabilizer –  Ground crew relatively unconcerned, advised “kick” –  Kick leads to nose-down, rapid descent

•  Final crash –  Regain control, head for LA –  “Loud bang” followed by rapid descent and crash

•  Did pilot make a final effort to control stabilizer?

MSE 200A Fall, 2008

Alaska 261 - Flight

MSE 200A Fall, 2008

The MD-80

MSE 200A Fall, 2008

Jack-screw assembly on the stabilizer

Jackscrew assembly that controls the horizontal stabilizer on the MD-80 series aircraft. [Boeing]

MSE 200A Fall, 2008

Jack-screw assembly on the stabilizer

MSE 200A Fall, 2008

Jack-screw assembly post-accident

MSE 200A Fall, 2008

Close-up of thread remnants

MSE 200A Fall, 2008

Acme nut

MSE 200A Fall, 2008

Wear to the Acme nut

MSE 200A Fall, 2008

Was the Jackscrew Greased?

•  No grease found beyond dried red-grey residues –  Mobil 28 is red, Aeroshell 33 is yellow –  Simple tests show immersion will not wear grease off

•  Lubrication should be added to nut through “zirc fitting” –  Passageway was blocked with old residues –  Blocked grease in passageway was red

MSE 200A Fall, 2008

Configuration at lower stop

MSE 200A Fall, 2008

Configuration at lower stop

•  After threads strip, screw slips through the nut –  until the nut contacts the lower stop

MSE 200A Fall, 2008

Final failure was torque tube fatigue

•  Nut released because of torque tube failure –  “Torque tube” is a solid bar inside the hollow screw

•  The torque tube failed in low-cycle fatigue

MSE 200A Fall, 2008

Could lower stop have supported the nut?

•  FEM (Boeing) says yes

•  Evidence of loading on stop –  Nut embedded in stop –  Severe rotation score on stop –  Severe rotational score on tube

•  Pilots responsible?

MSE 200A Fall, 2008

Metallurgical Findings - Epperson (NTSB)