HW5 Tips and Answers 

NOTE: If you are looking here before wrestling with the problems and trying to solve them first, you are not going to learn this material.


HW 5.1
The axial stress on the rod is 282.9MPa.  For the axial loading, Se Prime is 276.8MPa.  With all of the modifying factor equal to one, this is also Se.  The exponent b is -0.07398.  This results in N = 739,000 cycles.

HW 5.2 The Grinding Wheel Problem

The bending stress should be 22.0 ksi. Ksize is 0.939.  After reliability and surface modification factors,
Se should be 19.01 ksi.  Life should come out to 362,000 cycles.  That would only allow 
4827 parts to be ground before life would be up.  The bending stress must be reduced to the
endurance strength to have infinite life.


Here are additional suggestions for the homework:

1) Everything that you need should be in the lecture notes and Hamrock.
2) Definitely draw the S-N diagrams.