Installation
To conduct tests a bend-torsion machine for a pure bending of round specimens is used (Fig.3).
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 11. Do again point 10 for the remaining specimens reducing 12. Draw Wohlers curve using the test data 13. With Wohlers curve state the fatigue strength
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