tailieunhanh - Text Book of Machine Design Part 6

CONTENTS CONTENTS Variable Stresses in Machine Parts C H A P T E R n 181 Variable Stresses in Machine Parts 1. Introduction. 2. Completely Reversed or Cyclic Stresses. 3. Fatigue and Endurance Limit. 4. Effect of Loading on Endurance Limit—Load Factor. 5. Effect of Surface Finish on Endurance Limit—Surface Finish Factor. 6. Effect of Size on Endurance Limit—Size Factor. 8. Relation Between Endurance Limit and Ultimate Tensile Strength. 9. Factor of Safety for Fatigue Loading. 10. Stress Concentration. 11. Theoretical or Form Stress Concentration Factor. 12. Stress Concentration due to Holes and Notches. 14. Factors to be Considered while Designing Machine Par ts to Avoid. | CONTENTS C H A P T E R 6 Variable Stresses in Machine Parts 1. Introduction. 2. Completely Reversed or Cyclic Stresses. 3. Fatigue and Endurance Limit. 4. Effect of Loading on Endurance Limit Load Factor 5. Effect of Surface Finish on Endurance Limit Surface Finish Factor 6. Effect of Size on Endurance Limit Size Factor 8. Relation Between Endurance Limit and Ultimate Tensile Strength. 9. Factor of Safety for Fatigue Loading. 10. Stress Concentration. 11. Theoretical or Form Stress Concentration Factor 12. Stress Concentration due to Holes and Notches. 14. Factors to be Considered while Designing Machine Parts to Avoid Fatigue Failure. 15. Stress Concentration Factor for Various Machine Members. 16. Fatigue Stress Concentration Factor 17. Notch Sensitivity. 18. Combined Steady and Variable Stresses. 19. Gerber Method for Combination of Stresses. 20. Goodman Method for Combination of Stresses. 21. Soderberg Method for Combination of Stresses. Introduction We have discussed in the previous chapter the stresses due to static loading only. But only a few machine parts are subjected to static loading. Since many of the machine parts such as axles shafts crankshafts connecting rods springs pinion teeth etc. are subjected to variable or alternating loads also known as fluctuating or fatigue loads therefore we shall discuss in this chapter the variable or alternating stresses. Completely Reversed or Cyclic Stresses Consider a rotating beam of circular cross-section and carrying a load W as shown in Fig. . This load induces stresses in the beam which are cyclic in nature. A little consideration will show that the upper fibres of the beam . at point A are under compressive stress and the lower fibres . at point B are under tensile stress. After 181 CONTENTS Fig. . Reversed or cyclic stresses. 182 A Textbook of Machine Design half a revolution the point B occupies the position of point A and the point A occupies the position of point B. Thus the point B is