WORCESTER POLYTECHNIC INSTITUTEcfurlong/me3320/lect02/Lect02.pdf · Mechanical Engineering...
Transcript of WORCESTER POLYTECHNIC INSTITUTEcfurlong/me3320/lect02/Lect02.pdf · Mechanical Engineering...
Mechanical Engineering Department
WORCESTER POLYTECHNIC INSTITUTEMECHANICAL ENGINEERING DEPARTMENT
DESIGN OF MACHINE ELEMENTSME-3320, B’2020
Lecture 02
October 2020
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DO NOTE:
Watch the following short videos before coming to class
Tensile test:https://www.youtube.com/watch?v=D8U4G5kcpcM
Poisson’s ratio:https://www.youtube.com/watch?v=M_7Prst1Ysc
Fatigue test:https://www.youtube.com/watch?v=LhUclxBUV_E
Brinell Hardness testhttps://www.youtube.com/watch?v=RJXJpeH78iU
Charpy impact test:https://www.youtube.com/watch?v=tpGhqQvftAo
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P
P
ASTM standards
Material properties
Conventional tensile test
Strain:o
o
l
ll −=
Modulus of elasticity:
=E
oA
P=Stress:
(Average normal
stress)
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Average normal stress in an axially loaded bar
Tensile test
Necking
Typical results
Ductile material
Brittle material
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Average normal stress in an axially loaded bar: Poisson’s ratio
x
y
xx
yy
−=
Poisson’s ratio:
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Material properties
Microscale tensile test
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Material properties
Stress-strain diagrams: yield behavior
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Material properties
Tensile test
Necking
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Material properties
Compression test
Does not “fail” Shear failure
Even materials: same behavior in tension as in compression.
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Material properties
Bending test: three-point bending
FailureDoes not “fail”
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Material properties
Torsion test
Stress-strain relation
(torsion):
ol
Gr =
Modulus of rigidity:
)1(2 +=
EG
Ultimate shear strength
(torsion):
J
rTS
breakus
)(=
Not uniform stress distribution; (in some
cases, thin-walled tubes are preferred for this
test, why?)
Steels:utus SS 80.0=
Other ductile
mtls.: utus SS 75.0=
Note: ysy SS 58.0=
θ
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Material properties
Fatigue strength Sf and endurance limit SeTesting of wind turbine blades
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Material properties
Resilience and toughness: impact load
Toughness: =f
dUT
0
Resilience: =el
dUR
0
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Wind turbine test set-up on the UCSD-NEES Outdoor Shake Table at UCSD's Jacobs School of Engineering. The Table is capable of creating realistic simulations of the most devastating earthquakes ever recorded. The facility is part of the National Science Foundation's George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES).
Material properties
Resilience and toughness: impact load
Reference: http://www.jacobsschool.ucsd.edu/
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Material properties
Hardness: Brinell, Rockwell, and Vickers test
)( 22
2dDDD
FHB
−−=
psi , 30500BBut
HHS
Sut estimation using Brinell
hardness number:
MPa, 2.045.3BBut
HHS
Brinell test
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Material properties
Heat treatment
• Quenching: transformation temperature (steels 700 oC); rapid cooling; formation of martensite
• Tempering: quenching; reheated (200 - 700 oC -- lower than transformation temperature); cool slowly
• Annealing: reverses quenching and tempering; slow cooling rate
• Normalizing: similar to annealing, but faster cooling rate
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Material properties
Cold working
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Material propertiesCoatings and surface treatments: surface protection
(wear resistance, corrosion, etc.)
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Material properties
AISI/SAE designation of steel alloys
(represent hundredths of a percent of carbon present)
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Material properties
General properties
(AISI - American Iron & Steel Institute)
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Reading assignment
Homework assignment
Chapter 2 of textbook
Review notes and text: ES2001
Author’s:
Solve: 2-1, 2-4, 2-8, 2-15, 2-21