1. Mechanics of Materials Lab
Lecture 19
Fatigue
Mechanical Behavior of Materials Sec
Jiangyu Li
University of Washington 1
Jiangyu Li, University of Washington

2. Safety Factor with Mean Stress2
Jiangyu Li, University of Washington

3. 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 cycles
What is the safety factor in life and stress? 3
Jiangyu Li, University of Washington

4. Jiangyu Li, University of Washington
Multiaxial Stress
Figure: 09-40 4
Jiangyu Li, University of Washington

5. Jiangyu Li, University of Washington
Multiaxial Stress
Figure: 09-41 5
Jiangyu Li, University of Washington

6. Jiangyu Li, University of Washington
Example
A solid circular shaft of diameter 50mm is made of Ti-6Al-4V. A zero-to-maximum cyclic torque of T=10 kN.m is applied, together with a zero-to-maximum cyclic bending moment of M=7.5 kN.m applied in phase with same frequency. What is the fatigue life? 6
Jiangyu Li, University of Washington

7. Jiangyu Li, University of Washington
Example
A solid circular shaft is made of AISI 4142 steel with diameter of 50mm, and loaded in cyclic torsion between zero and a torque of 20 kN.m.
What is fatigue life
What shaft diameter is needed if cycles are expected in life and safety factor must be at least 20 7
Jiangyu Li, University of Washington

8. Jiangyu Li, University of Washington
Assignment
Mechanical Behavior of Materials
9.30, 9.31,9.33 , 9.35, 9.39 8
Jiangyu Li, University of Washington