MSE113_Intro-2009 - Departments of Materials Science...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Departments of Materials Science & Engineering University of California, Berkeley Mechanical Properties of Engineering Materials Robert O. Ritchie MSE 113 Fall 2009 MSE 113 Mechanical Behavior of Engineering Materials Lecturer: Prof. R. O. Ritchie, Rm. 216 HMMB (or 62-239, MSD, LBNL) tel: Amanda Runciman, email: Webpage: http://www lbl gov/Ritchie/Teaching/MSE113/ BRIEF COURSE DESCRIPTION: A presentation is given of deformation and fracture in engineering materials materials, including elastic and plastic deformation from simple continuum mechanics and microscopic viewpoints, dislocation theory, alloy hardening and creep deformation, fracture mechanisms, linear elastic and nonlinear elastic fracture mechanics, toughening of metals, ceramics and composites, environmentallyassisted cracking, fatigue failure, subcritical crack growth, stress/life and damagetolerant design approaches. GRADING: Homeworks: Mid-Term I: Mid-Term II: Mid T II Final: 15% 20% 20% 45% MSE 113 Required and Reference Texts M.A. Meyers, K K. Chawla: Mechanical Behavior of Materials (Cambridge, 2009, 2nd ed.) (required text) Mechanical Behavior of Materials: Materials: F.A. McClintock, A.S. Argon: Mechanical Behavior of Materials (Addison-Wesley, 1966)* M. A. Meyers, K.K. M A Meyers K K Chawla: Mechanical Metallurgy: Principles and Applications (Prentice Hall 1984) (Prentice-Hall, R.W. Hertzberg: Deformation and Fracture Mechanics of Engineering Materials (Wiley, 1989, 4th ed.) Fracture Mechanics: Mechanics: T.L. Anderson: Fracture Mechanics: Fundamentals and Applications (CRC Press, 1999, 3rd ed.)* D. D Broek: Elementary Engineering Fracture Mechanics (Sijthoff and Noordhoff 1982 3rd ed ) Noordhoff, 1982, ed.) J.F. Knott: Fundamentals of Fracture Mechanics (Halstead Press, 1973)* S.T. Rolfe, J.M. Barson: Fracture and Fatigue Control in Structures (Prentice-Hall, 1987, 2nd ed.) H. L. Ewalds, R. J. Wanhill: Fracture Mechanics (Arnold, 1984)* B.R. B R Lawn: Fracture of Brittle Solids (Cambridge Univ Press 1993 2nd ed ) Univ. Press, 1993, ed.) Fatigue: Fatigue: S. Suresh: Fatigue of Materials (Cambridge Univ. Press, 1998, 2nd ed.)* EnvironmentallyEnvironmentally-Influenced Failure: Failure: J.C. J C Scully: Fundamentals of Corrosion (Pergamon 1975 2nd ed ) (Pergamon, 1975, ed.) Mechanical Testing: Testing: Metals Handbook, 9th ed., vol. 8 (American Society for Metals) Failure Analysis/Fractography: Analysis/Fractography: Metals Handbook 9th ed vol 12 (American Society for Metals) Handbook, ed., vol. Continuum Mechanics/Elasticity: Mechanics/Elasticity: E.P. Popov: Introduction to Mechanics of Solids (Prentice-Hall, 1968) S.H.Crandall, N.C.Dahl, T.J.Lardner: Introduction to the Mechanics of Solids (McGraw, 1978, 2nd ed.) MSE 113 Course Outline Aug. 27: Sep. 1: Sep. 3: Sep. 8: Sep. Sep 10: Sep. 15: Sep. 17: Sep. 22: Sep. 24: Sep. 29: Oct. 1: Oct. 6: Oct. 8: Oct. 13: Oct. 15: Oct. 20: Oct. 22: Oct. 27: Oct. 29: Nov. 3: Nov. Nov 5: Nov. 10: Nov. 12: Nov. 17: Nov. 19: Nov. 24: Dec. 1: Dec. 3: Dec. 8: Dec. 15: Introduction Continuum Deformation Continuum Deformation Elasticity Elasticity Plasticity Dislocations: definition & theory Dislocations: motion Dislocations: partials MIDMID-TERM EXAM I Single Crystal Slip Alloy Hardening: mechanisms Creep: Creep: Deformation Creep: mechanisms Fracture: Fracture mechanisms Fracture Mechanics: introduction Linear Elastic Fracture Mechanics: K fields Linear Elastic Fracture Mechanics: KIc testing Linear Elastic Fracture Mechanics: resistance curves MIDMID-TERM EXAM II Nonlinear Elastic Fracture Mechanics: J fields Toughening Mechanisms: metals Toughening Mechanisms: ceramics Toughening Mechanisms: composites EnvironmentallyEnvironmentally-Assisted Cracking mechanics Cracking: Fatigue: , p S/N curve, Goodman relationship Fatigue-Crack Propagation Damage-Tolerant Design: lifetime calculations Review session (not mandatory) FINAL EXAMINATION (5 – 8 pm) Why Mechanical Properties are Important • Why does stuff fail? • How does it fail? • What type of stuff fails? ( • ships, bridges and planes Sknyliv Airshow, Airshow, Lviv, Lviv, Ukraine (2002) ( ) • micromachines • medical d i di l devices Tacoma Narrows suspension bridge (1940) • you! (bones, teeth) • Can we prevent it? ( B-52 bomber, Fairchild Air Force Base, WA (1994) Length Scales in Material Behavior Atomic structure sub-nanometer 10 (<10-10 m) Si3N4 jet engine 1m 0.09 nm prosthetic device 10 mm ceramic crystal Dentin 0.1 0 1 nm Enamel Macro Structures cm to m (10-2 to 1 m) 0.275 nm Microstructures micrometers (~10-3 m) micromachines 10 m i hi crack in a human tooth 1 m fatigue crack in Ni alloy blade 10 m MEMS/NEMS – Micro/ NanoNanoelectromechanical systems How do things break? • by plastic deformation - yielding - e.g., by bending a paper clip e.g., • by (instantaneous) fracture - e.g., by breaking a pencil or a tooth or by impact fracture e.g., • by fatigue (delayed fracture) - e.g., by bending that paper clip back and forth several times e.g., • by environmentally-assisted cracking ( y environmentallyy g (delayed fracture) y ) - e.g., by bending that paper clip back and forth under (salt) water e.g., • by corrosion and/or wear (surface damage) - e.g., by corroding away or simply wearing something out e.g., Failure by Plastic Deformation • plastic (permanent) deformation of a bridge • deformation led to eventual collapse • Tacoma Narrows suspension bridge, near Puget Sound, failed on at 11 am Sound Nov. 7, 1940, after only having been open for traffic a few months How do things break? • by plastic deformation - yielding - e.g., by bending a paper clip e.g., • by (instantaneous) fracture - e.g., by breaking a pencil or a tooth or by impact fracture e.g., • by fatigue (delayed fracture) - e.g., by bending that paper clip back and forth several times e.g., • by environmentally-assisted cracking ( y environmentallyy g (delayed fracture) y ) - e.g., by bending that paper clip back and forth under (salt) water e.g., • by corrosion and/or wear (surface damage) - e.g., by simply corroding away or wearing something out Instantaneous Impact Fracture • 500 T2 tankers and 2700 Liberty ships were built during WWII • prefabricated all-welded allconstruction, with brittle steel • one vessel was built in 5 days! Brittle fracture of SS Schenectady, Jan. 1943 • initially, some 30% of Liberty ships suffered catastrophic failure p p • cracks started at stress concentrations (e.g., hatchways) (e.g., and propagated rapidly through the steel hull as the metal became too brittle at low temperatures SS John P. Gaines split in two in 1943 Instantaneous Impact Fracture • Air France charter flight from Paris to New York - July 25, 2000 y , • the Concorde crashed into a hotel shortly after take-off, 5 miles from takeairport, with 109 fatalities airport • attributed to a piece of metal on the runway causing the bursting of a tire f ti • the impact of the tire debris on the fuel tank punctured it, leading to loss of engine power, and the subsequent crack foreign• an example of foreign-object damage (FOD) How do things break? • by plastic deformation - yielding - e.g., by bending a paper clip e.g., • by (instantaneous) fracture - e.g., by breaking a pencil or a tooth or by impact fracture e.g., • by fatigue (delayed fracture) - e.g., by bending that paper clip back and forth several times e.g., • by environmentally-assisted cracking (delayed fracture) y environmentallyy g( y ) - e.g., by bending that paper clip back and forth under (salt) water e.g., • by corrosion and/or wear (surface damage) - e.g., by corroding or simply wearing something out e.g., Fatigue & Delayed Fracture • De Havilland Comet, first commercial jet aircraft, had five major crashes in j 1952 - 54 period • caused by fatigue cracks initiated at square windows, windows driven by cabin pressurization and depressurization • Aloha Airlines Boeing 737, in route from Hilo to Honolulu (April 1998) undergoes explosive decompression – 1 fatality p p y • caused by a weakening of the fuselage due to corrosion and small cracks – led to Aging Aircraft Initiative McDonnell Douglas DC-10 Crashes DC• McDonnell–Douglas DC-10 is a threeMcDonnell– DCthreeengine medium-range wide-body aircraft mediumwide• the aircraft suffered many notable crashes - March 3, 1974 (Paris) - Turkish Airlines flight 981, rear cargo door blew out – all 333 passengers & 12 crew lost July 19, 1989, Souix City, Iowa - May 25, 1979 (Chicago) - American Airlines 191 lost left engine on take-off – takeall 258 passengers & 13 crew lost - July 19 1989 (Souix City) – United Airlines 19, (Souix 232 crashed killing 110 of 258 passengers ( a fatigue crack in the fan disk in the tailedtailedmounted engine fractured the disk; the resulting d b i severed all th lti debris d ll three h d li hydraulic control systems. The only way to steer the plane was by adjusting the thrust of the two remaining wing-mounted engines. wingHowever, on l di th ti of th right H landing the tip f the i ht wing contacted and the aircraft skidded, somersaulted and caught fire. United 232 Souix City Iowa Crash GE CF6-6 CF6engine • Ti alloy (Ti-6Al-4V) fan disk fractured due to 0.6-inch (Ti-6Al0.6fatigue crack, that initiated from a 0.015-0.055 inch 0.015inclusion in the cast metal fan disk • the crack from the bore grew for many years and was missed by some 6 inspections • debris from failure severed all hydraulic control lines • parts of the fractured fan disks were not found for several f df l months July 19, 1989, Souix City, Iowa reconstructed fan disk 1 inch How do things break? • by plastic deformation - yielding - e.g., by bending a paper clip e.g., • by (instantaneous) fracture - e.g., by breaking a pencil or a tooth or by impact fracture e.g., • by fatigue (delayed fracture) - e.g., by bending that paper clip back and forth several times e.g., • by environmentally-assisted cracking ( y environmentallyy g (delayed fracture) y ) - e.g., by bending that paper clip back and forth under (salt) water e.g., • by wear (surface damage) - e.g., by simply wearing something out e.g., Failure due to Wear • A major wear problem is with railroad tracks, where surface wear from metal-tof f metal-tometal rolling contact can damage the rails leading to derailment Rail collapse leads to derailment of a locomotive in UK, in 1981 crack initiation Derailment of 100 ton tank wagon and the rest of the train in Lincolnshire, UK in 1982 (from surface wear f (delamination) delamination) can lead to catastrophic fatigue fracture of the rail Fractography Ductile fracture 5 m Brittle fracture 20 m Fatigue fracture Creep fracture Ductile Fracture microvoid coalescence “cup-and“cup-and-cone” ductile fracture “flat” brittle fracture • ductile fracture is the “desirable” form of fracture as it requires high energy • i results f it l from the coalescence of small h l f ll voids formed around particles, e.g., inclusions, precipitates, in the metal (ASM Metals Handbook, vol. 12, 1987) Brittle Fractures • most materials are polycrystalline consisting of many crystals (grains) • b ittl f t brittle fracture is generally t i ll transgranular l (cleavage) with the crack propagating through the grains • when th grain h the i boundaries are “embrittled”, fracture embrittled”, can be intergranular 20 m transgranular cleavage • segregation of impurity e e e t atoms, e g , element ato s, e.g., S, e.g., P, O, H, to grain boundaries can cause such embrittlement 10 m 20 m intergranular fracture Ductile-toDuctile-to-Brittle Transition Many materials, like steels (and rubber), show a ductile-toductile-to-brittle transition (glass transition) microvoid coalescence Toughness (fracture energy) transgranular cleavage DBTT transition temperature Temperature p • Rubber shows a glass transition temperature, below which it is brittle, like glass, and above which it behaves like rubber 20 m • Similarly, many metals like steel display a ductile-to-brittle Similarly ductile-totransition temperature. Above this temperature, they are ductile, whereas below they are brittle with typically an order of magnitude lower toughness (energy required for fracture) Sinking of the RMS Titanic • On April 14, 1912, RMS Titanic hit an iceberg in the north Atlantic and sank in just over 2 hrs • 1500 of Titanic’s 2223 p passengers lost g Why did the ship sink so fast? 1. poor steel: steel was very brittle with high O & S content 2. poor rivets: hull held together by 3 million very brittle wrought iron rivets containing excessive slag (Encyclopedia Britannica,; The Gazette Online, vol. 28 (32) 1999; Fatigue Fractures • more than 80% of all failures are caused by fatigue, i.e., prolonged fatigue, i.e., failure under cyclic (alternating) loads • to the naked eye, fatigue fractures are characterized by smooth, “half-moon”, “halfregions with radiating bands • microscopically, smaller bands, called striations, striations, can often be seen – these are the location of the crack each cycle mediummediumC steel housing crack initiation sites 1 m (after D. J. Wulpi, ASM Metals Handbook, vol. 12, 1987) Fatigue vs. Instantaneous Failure Failure of an axial shaft (e.g., a car’s steering column or axle) (e.g., medium carbon steel (AISI 1050) automobile axle Fatigue (rotary) failure F ti ( t ) f il Bending (overload ) fracture • a fatigue failure would imply a process that has occurred over some period of time, and would have likely caused the accident • an overload fracture would be an instantaneous event likely caused by the accident (after Z. Flanders, ASM Metals Handbook, vol. 12, 1987) What about small structures? MEMS human hair micromachine (Elliot Hui, BSAC) 10 m • The dimensions of current micromicromachines (MEMS) are on the order of micrometers (microns – m), i.e., i.e., millionths of a meter • next generation machines (NEMS) may be on the order of tens to hundreds of nanometers ( ) (nm), i.e., i.e., nearly a trillionth of a meter! • a silicon MEMS micromotor next to a strand of human hair • the diameter of the hair is about 50 m (50,000 nm!) What are Micromachines? • Micromachines are known as MEMS • micro-electro-mechanical-systems icro- lectro- echanical- • many applications are used today • i ti l sensors (e.g., i air b inertial (e.g., in i bags) ) • medical devices y g • memory and mass storage • micro-mirrors for digital projection micro- • not to mention future applications Analog Devices air bag sensor • “pocket turbines” (to power the soldier of the future!) • Next generation of machines may even be smaller - NEMS • nano-electro-mechanical-systems lectro- echanical- Micromachines or MEMS R. Conant, 1999 Schmidt et al, MIT micronmicron-scale moveable mirrors microturbine MCNC/Cronos gears 50 m microhinge Applications: cogs and gears Sandia Nat.Labs • Micron-scale cogs and gears are used Micronextensively in mechanical micromachines 10 m Applications: Micromotors • Sandia microengine moving to rotate gears in a 20,000 to 1 reduction ratio to operate a set of microtweezers Chris Keller • it is powered by two orthogonal electrostatic motors 10 m • Microtweezers used for micromicromanipulation i l ti courtesy Sandia National Laboratories, SUMMiT™ Technologies, Micromotors and Bugs! two dust mites on a rotor wheel spider mite crossing a gear spider mite “tests” a tests micromirror p aphid on a micromirror spider mite rides a g large wheel 10 m ..and it gets a wee bit too fast! courtesy Sandia National Laboratories, SUMMiT™ Technologies, Mechanical Testing at the Microscale test sample • bulk silicon is not susceptible to fatigue • fatigue due to moisturemoisture-induced nanoscale cracks in SiO2 oxide layer Stress Amplitude (GPa) s e, • 2 m thick n-type polysilicon nthin films fail at >109 cycles at half their strength MUMPs 18 S N (pres).Q PC 4 2.5 Minute HF Release 3.0 Minute HF Release Fatigue S/N curve 3 2 1 Notched Polycrystalline Silicon Beam stress = load/area Laboratory Air 0 5 10 10 6 10 7 10 8 10 9 10 10 10 11 10 Fatigue Life, N f (C l ) F ti Lif (Cycles) oxide resonant mass 300 m Brown, Van Arsdell, Muhlstein et al al. testing to >1011 cycles comb drives Unthi nned HVT EM HVTEM 0.8 MeV 2 m unthinned sample notch tip region Muhlstein, Stach, Ritchie, Acta Mater., 2002 12 NEMS Mechanical Testing Device • Nano-cantilever: fracture and fatigue at the nano-scale Nanonano- 100 nm • smallest feature size ~20 nm; fabricated using a nanowriter single crystal silicon from D.H.Alsem, E.A.Stach, J.A.Liddle, D.H.Alsem, E.A.Stach, J.A.Liddle, R.O.Ritchie Alloptropic Forms of Carbon diamond graphite • all strong (covalent) bonds • strong bonds in layers • weak (Van der Waals) bonds between layers a = 0.534 nm carbon C60 • all strong (covalent) bonds carbon nanotubes • strong bonds in tubes • weak bonds between tubes single wall carbon C70 multi wall Mechanical Testing of Carbon Nanotubes • Carbon nanotubes, few nm in diameter, nanotubes, claimed to be the world’s strongest material! in situ mechanical test in TEM to measure the strength of a 1212-nm thick carbon nanotube TEM image Denchzk, Ritchie, Zettl, et al. • Strength of the nanotube was measured as 150 GPa, GPa, i.e., roughly 5 times stronger than Kevlar or carbon fibers and more than 50 times stronger than hardened steel New NEMS Machines • by reversing the electrical current along a CNT, can metal can be transported along the tube • by putting the metal globs between two nanotubes, we can nanotubes, move then apart and do work ( (linear nano-motor) nano) linear nano motor nano-motor carbon nanotube globs of indium animation i ti 5 nm TEM image • motor force ~1 nN • power densities ~ 20 MW/m3 - 8 GW/m3 metal transport toward cathode 2 nm thermallythermally-activated electricallyelectricallydirected In surface diffusion Regan, Aloni, Ritchie, Dahmen, Zettl, Nature, 2004 Aloni, Dahmen, Zettl, Nature, Regan, Aloni, Ritchie, Zettl, Nano Lett., 2005 Aloni, Zettl, Lett. ...
View Full Document

Ask a homework question - tutors are online