When you ask a question, do you really want to know the answer, or are you merely flaunting your power?

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When you ask a question, do you really want to
know the answer, or are you merely flaunting your
power? -Dmitri Harkonnen
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Today's objective how to make these guys work
harder
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So what happened (coat hanger)?
Dislocations moved when coat hanger bent
Dislocation generators produced large amounts of
new dislocations
New dislocations so numerous that they
entangled had difficulty moving
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So.cheap, convenient way to strengthen mat'ls
On the other hand, work hardening can be problem
Example cold rolling plate to sheet
too hard to continue rolling
harder!!
harder
fairly soft
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With each other annihilate entangle form
generators
With grain boundaries disappear pileups
Thus, small grained mat'ls stronger cuz more
grain bdy area, gt more pileups
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With tiny precipitate particles
Why don't dislocs move thru precipitates? a.
complex structure - poorly defined slip
planes and/or b. slip planes wrongly oriented
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Solute atoms different size than solvent atoms
Crystal structure distorted slip planes less
well-defined Disloc movement restricted
Cu solid solutions
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Work hardening Solution hardening Precipitation
hardening Grain size reduction
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Oh, yeah.one more thing about dislocs
Ease of disloc motion depends on slip plane
orientation
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Slip occurs only as a result of shear only
along slip plane in a slip direction
The greater the no. of slip systems, the greater
the probability some slip plane slip direction
correctly oriented
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Slip system slip plane slip direction
ccp - 12 slip systems hcp - 3 slip
systems
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Assignments for next class 1. review today's
classnotes a. work hardening b. dislocation
tangles c. precipitation hardening d.
solution hardening e. grain boundary
pileups f. slip systems and critical
resolved shear stress 2. Exam comments