1 Jiangyu Li, University of Washington Lecture 15 Fatigue Mechanical Behavior of Materials Sec Jiangyu Li University of Washington Mechanics of Materials Lab

2 Jiangyu Li, University of Washington S-N Diagram

3 Jiangyu Li, University of Washington Safety Factor

4 Jiangyu Li, University of Washington Example 9.10 For AISI 4340 steel in Table 9.1, a life of 1.94x10 5 cycles to failure is calculated for the stress amplitude of  a =500 Mpa. Suggestion is made that parts of this type be replaced when the number of cycles applied reach 1/3 of the life. a)What is the safety factors in life and in stress b)Is the suggestion good?

5 Jiangyu Li, University of Washington Facture Mechanics Method of Fatigue

6 Jiangyu Li, University of Washington Crack Growth > >

7 Jiangyu Li, University of Washington Fatigue Life

8 Jiangyu Li, University of Washington Fatigue Crack Growth Rate

9 Jiangyu Li, University of Washington Crack Grow Rate

10 Jiangyu Li, University of Washington Crack Growth Rate

11 Jiangyu Li, University of Washington Effect of R Ratio

12 Jiangyu Li, University of Washington Example For a bar subjected to 0<M<1200lb · in, S ut =185kpsi, S y =170kpsi, K ic =74kpsi·in 1/2, C= (in/cycle)/(kpsi·in 1/2)m, m=3.0, a=0.004in. Estimate N f.

13 Jiangyu Li, University of Washington Example Initial estimate, F=1

14 Jiangyu Li, University of Washington Assignment Mechanical Behavior of Materials 11.3, 11.7