ENG1001 Lecture Notes - Lecture 5: Ductility, Work Hardening, Wrinkle
30 May 2018
School
Department
Course
Professor
Slip
If#we#apply#a#force#to#try#to#move#2#planes#over#each#other,#we#MUST#rupture#
bonds#between#atoms.#Stress#required#is#about#E/15,#which#is#REALLY#high.
Dislocation
Metals#crystals#contain#defects.#Most#impt#is#line#defect/dislocation
=#distortion#in#a#crystal#lattice# along#a#line
Allows#slip#to#proceed#at#stresses#lower#than#the#predicted#yield#stress
Disruption#to#system#caused#by#moving#a#dislocation#<#disruption#required#to#
move#whole#atom#planes
When#dislocation#that#was#in#crystal#moves#to#end#of#crystal,#leaves#a#
permanent#deformation/"step"
**like# pulling#a#carpet.#Easier#to#push#wrinkle#in#the#middle#to#the#end#of#carpet#
than#pull#it#along#the#floor
Work/hardening
=#method#to#strengthen#material# while#balancing#yield#strength#and#
ductility,#by#restricting#dislocation#movement#(other#methods#include#alloys)
During,#number#of#dislocations#DRAMATICALLY#INCREASES,#thus#distance#
between#dislocations#increases.
On#average,#strain#interactions#repulsive,#dislocation#movement#restricted
Reverse =#annealing#-->#higher#ductility
Cold/work
*100%.
Dislocation/density/[length#of#all#dislocation#lines/m3or#m2]
Still#hard#either#way.
Typically#1010 -1014 m/m3
Still#<#number#of#atoms
Yield/strength/graph
Week$5:$Work$hardening,$dislocations$and$recovery
Friday,#18#August#2017
16:19
