Installation

 

To conduct tests a bend-torsion machine for a pure bending of round specimens is used (Fig.3).

Fig.3. The bend-torsion machine to test the pure bending of the round specimens under torsion

 

 

Specimen 1 is held in the torsion grips 2 and 3. The load creates the effort by hanging on shackles 4 and 5. Counter 6 fixes the cycle N number. Electric motor 7 is disconnected automatically by contact 8 when the specimen is broken. The bending moment diagram is shown in Fig.3.

The maximum normal stress is determined by the formula

 

where d is the specimen diameter of the work part,

W is the section modulus of the specimen cross-section,

M is the bending moment, F is the load.

The test specimen is manufactured under GOST 25.502-79 (fig. 4).

 

 

Fig.5. The specimen for test

Order

1. Choose the load diagram.

2. Choose the test machine or the stand.

3. Set the test base number N=10⁷.

4. Set the maximum cycle stress for the first specimen .

5. Insert the specimen in the machine.

6. Put the loads corresponding the stress .

7. Switch on the electric motor.

8. Do the loading of the specimen up to the rupture.

9. Write down the cycle number N which the specimen has endured.

10. Do again point 4 for the second specimen setting and points .

11. Do again point 10 for the remaining specimens reducing in 0, 1 .

12. Draw Wohlers curve using the test data and N (Fig.2).

13. With Wohlers curve state the fatigue strength .