lecture 24 fatigue mechanical behavior of materials sec. 9.6-9.8 jiangyu li
DESCRIPTION
Mechanics of Materials Lab. Lecture 24 Fatigue Mechanical Behavior of Materials Sec. 9.6-9.8 Jiangyu Li University of Washington. S-N Diagram. Fatigue Failure Criteria. Effect of Mean Stress. Effect of Mean Stress. Example: Gerber Line. - PowerPoint PPT PresentationTRANSCRIPT
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1 Jiangyu Li, University of Washington
Lecture 24Fatigue
Mechanical Behavior of Materials Sec. 9.6-9.8
Jiangyu LiUniversity of Washington
Mechanics of Materials Lab
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2 Jiangyu Li, University of Washington
S-N Diagram
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3 Jiangyu Li, University of Washington
Fatigue Failure Criteria
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4 Jiangyu Li, University of Washington
Effect of Mean Stress
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5 Jiangyu Li, University of Washington
Effect of Mean Stress
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6 Jiangyu Li, University of Washington
Example: Gerber Line
AISI 1050 cold-drawn bar, withstand a fluctuating axial load varying from 0 to16 kip. Kf=1.85; Find Sa and Sm and the safety factor using Gerber relation
Sut=100kpsi; Sy=84kpsi; Se’=0.504Sut kpsi
1
1)( 2
r
SS
SS
ut
m
e
a
kpsiK
kpsid
F
aofma
moa
ao
38.8
,53.443
Changeover
Table 7-10
1
2
3
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7 Jiangyu Li, University of Washington
Example
• AISI 4340 steel is subjected to cyclic load with a tensile mean stress of 200 MPA– What is the fatigue life for stress amplitude
of 450 MPA– Estimate the relationship between stress
amplitude and fatigue life for this mean stress
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8 Jiangyu Li, University of Washington
Safety Factor with Mean Stress
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9 Jiangyu Li, University of Washington
Example
• Man-Ten steel subject to stress amplitude of 180 Mpa and mean stress of 100PMa for 20000 cycles– What is the safety factor in life and
stress?
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10 Jiangyu Li, University of Washington
Safety Factor with Mean Stress
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11 Jiangyu Li, University of Washington
Example
• Man-Ten steel (f’=1089MPa, b=-0.115) subject to stress amplitude of 180 Mpa and mean stress of 100PMa for 20000 cycles– What is the safety factor in life and stress?
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12 Jiangyu Li, University of Washington
Assignment
Mechanical Behavior of Materials
9.30, 9.31,9.33 , 9.35