Mechanics of Materials Lab Lecture 19 Fatigue Mechanical Behavior of Materials Sec. 9.6-9.8 Jiangyu Li University of Washington 1 Jiangyu Li, University of Washington

Safety Factor with Mean Stress 2 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? 3 Jiangyu Li, University of Washington

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

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

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

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 100000 cycles are expected in life and safety factor must be at least 20 7 Jiangyu Li, University of Washington

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