Mechanics of Materials Lab Lecture 24 Fatigue Mechanical Behavior of Materials Sec. 9.6-9.8 Jiangyu Li University of Washington 1 Jiangyu Li, University of Washington

Jiangyu Li, University of Washington S-N Diagram 2 Jiangyu Li, University of Washington

Fatigue Failure Criteria 3 Jiangyu Li, University of Washington

Jiangyu Li, University of Washington Effect of Mean Stress 4 Jiangyu Li, University of Washington

Jiangyu Li, University of Washington Effect of Mean Stress 5 Jiangyu Li, University of Washington

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 Table 7-10 2 Change over 1 3 6 Jiangyu Li, University of Washington

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 7 Jiangyu Li, University of Washington

Safety Factor with Mean Stress 8 Jiangyu Li, University of Washington

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? 9 Jiangyu Li, University of Washington

Safety Factor with Mean Stress 10 Jiangyu Li, University of Washington

Jiangyu Li, University of Washington Example Man-Ten steel (sf’=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? 11 Jiangyu Li, University of Washington

Jiangyu Li, University of Washington Assignment Mechanical Behavior of Materials 9.30, 9.31,9.33 , 9.35 12 Jiangyu Li, University of Washington