1. Failure Criteria and stress concentration
Experiment 1
Failure Criteria
and stress concentration

4. Static failure criteria
Ductile material ( )
Max. Shear theory
Distortion energy
Ductile Coulumb-Mohr
2. Brittle material ( )
Max. normal stress
Brittle Coulumb-Mohr and modification

5. Maximum shear theory
Case 1
Case 2
Case 3

6. Distortion energy theory
Von Mises stress
Plain stress or plain strain
In general form

7. Maximum normal stress theory

8. Coulumb-Mohr and modification

9. S value

10. Various load Fatigue Testing
D=5mm or 10mm

11. Endurance limit for cast iron (Sn)

12. Correction of endurance limitSn
S’n
S’n Sn

13. Stress concentration and stress raisers
Stress concentration factor

14. Varying stress in machine element

15. Solving problems in which the stress is a combination of alternating stress and constant stress
For compression mean load, no effect on endurance limit

22. Designing for variable load and finite life

23. How to raise the endurance strength
1. Autofrettage

24. 2. Shot peening and surface rolling
3. Heat treatment
4. Laser treatment
5. Electro polishing
6. Others

25. Design Procedures Static Load design
Determine the external force, and configuration of the structure.
Determine the material of the structure.
Find the equation(s) of the stress in the structure.
Determine the criteria of failure to be used.
Find the S value of the structure.
According to the S value find the appropriate shape of the cross section.

26. Design for the various load
Determine the type of the external force, and configuration of the structure.
Determine the material of the structure.
Use fully corrected endurance limit for bending, Sn.
Apply stress concentration factors to torsion, bending and axial stress components.
Multiply any alternating axial stress component by the factor
Enter the resultant stress in to a Mohr’s circle analysis and find the principle stresses.
Find the Von mises alternating stress
Find the Sa/N according the failure criteria used.
Compare Von mises stress with Sa/N to find the dimension of the part.

27. Practices 1
Try to write an Excel program which can calculate the principle static stress, principle shear stress, Von Mises stress of a simply support beam of circular cross section under bending load, axial load and torsion load. (see figure in next page)
Use Distortion energy theory to find the dimension of the beam under the loads given in the figure in next page.

28. Fb FC
Torque
450
1000
Fb=10kg
Fc=10kg
Torque=10 N-m
Material : ultimate strength = 400MPa
Yielding strength =250MPa

29. Practices 2
Try to write an Excel program which can used the Solderburg Criteria to calculate Sa under different loading conditions and safety factor N.
Use Von mises stress to find the dimension of the beam under the loads given in the figure of practice 1. If all the load is varied as shown in figure (c) of following page. The surface of the beam is machined (please write a Excel program to do this).