WORCESTER POLYTECHNIC INSTITUTEcfurlong/me3320/lect02/Lect02.pdf · Mechanical Engineering...
Transcript of WORCESTER POLYTECHNIC INSTITUTEcfurlong/me3320/lect02/Lect02.pdf · Mechanical Engineering...
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Mechanical Engineering Department
WORCESTER POLYTECHNIC INSTITUTEMECHANICAL ENGINEERING DEPARTMENT
DESIGN OF MACHINE ELEMENTSME-3320, B’2020
Lecture 02
October 2020
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Mechanical Engineering Department
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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Mechanical Engineering Department
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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Mechanical Engineering Department
Average normal stress in an axially loaded bar
Tensile test
Necking
Typical results
Ductile material
Brittle material
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Mechanical Engineering Department
Average normal stress in an axially loaded bar: Poisson’s ratio
x
y
xx
yy
−=
Poisson’s ratio:
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Mechanical Engineering DepartmentUIUC/Sandia Labs
Material properties
Microscale tensile test
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Mechanical Engineering Department
Material properties
Stress-strain diagrams: yield behavior
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Mechanical Engineering Department
Material properties
Tensile test
Necking
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Mechanical Engineering Department
Material properties
Compression test
Does not “fail” Shear failure
Even materials: same behavior in tension as in compression.
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Mechanical Engineering Department
Material properties
Bending test: three-point bending
FailureDoes not “fail”
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Mechanical Engineering Department
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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Mechanical Engineering Department
Material properties
Fatigue strength Sf and endurance limit SeTesting of wind turbine blades
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Mechanical Engineering Department
Material properties
Resilience and toughness: impact load
Toughness: =f
dUT
0
Resilience: =el
dUR
0
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Mechanical Engineering Department
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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Mechanical Engineering Department
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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Mechanical Engineering Department
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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Mechanical Engineering Department
Material properties
Cold working
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Mechanical Engineering Department
Material propertiesCoatings and surface treatments: surface protection
(wear resistance, corrosion, etc.)
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Mechanical Engineering Department
Material properties
AISI/SAE designation of steel alloys
(represent hundredths of a percent of carbon present)
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Mechanical Engineering Department
Material properties
General properties
(AISI - American Iron & Steel Institute)
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Mechanical Engineering Department
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