FACTOR OF SAFETY AND ITS SELECTION

FACTOR OF SAFETY IN MACHINE DESIGNING

CONTENTS
1 MACINE DESIGNING
2 FACTOR OF SAFETY
3 FOS FORMULAE
4 DUCTILE AND BRITILE MATERIAL
5 IMPORTANCE OF FOS
6 SELECTION OF FOS
7 FACTORS AFFECTING FOS
8 DESIGN FACTOR VS SAFETY FACTOR
9 MARGIN FACTOR
9 EXAMPLES
10 CONCLUSION

1. MACHINE DESIGN Factor of safety and its selecction BY DENIS SORENG

2. Machine Design is the creation of new and better machines and improving the existing ones. MACHINE DESIGNING COST EFFICIENCY MANUFACTURABILITY STRENGTH RIGIDITY SAFETY...........

3. FACTOR OF SAFETY While designing any Engineering product or component, safety is of utmost importance. To ensure the safety of those items, each component is designed to bear more loads than its actual operating loads. So, there will always be some margin or cushion as compared to its operating capabilities. This is ensured during the design stage by considering a suitable factor of safety. example :

4. WAYS TO EXPRESS FOS ACTUAL LOAD / WORKING LOAD YEILD STRESS / WORKING STRESS FAILURE LOAD / DESIGN LOAD ULTIMATE STRESS / WORKING STRESS As understood from the above equation the allowable stress is always less than the ultimate failure stress. Hence, the factor of safety is always greater than 1.

5. ductile britile yeild stress / working stress ultimate stress / working stress

6. SIGNIFICANCE EXAMPLE FOS = MAX STRESS / WORKING STRESS MS = 360 N/mxm FOS =4 4 =360 / working stress working stress = 90 N/mxm

7. IMPORTANCE OF FOS HIGH CHANCE THAT PRODUCT WON'T FAIL THERE WILL BE FEWER CHANCE OF HUMAN INJURY OR DEATH PRODUCT WILL BE QUICKLY APPROVED BY A REGULATORY AGENCY EASY TO LAUNCH THE PRODUCT IN THE MARKET LESS PRODUCT RECALL ISSUE INCREASE CUSTOMER SATISFACTION

8. SELECTION OF FOS MORE FOS MORE SAFE CONCEPT OF FAILURE LESS FOS LESS SAFE INCREASE IN LOAD DECREASE IN CAPACITY

9. FACTORS AFFECTING FOS UNPREDICTABLE LOADS FATIGUE CREEP THERMAL STRESS MANUFACTURING COMPENSATION MATERIAL PROPERTIES WORKING ENVIROMENT POSSIBLE MISUSE ETC . . . .

10. Design factor VS safety factor Design factor is basically how much load a part is REQUIRED to withstand and the safety factor is the amount of load a part could ACTUALLY be able to withstand. So the design factor is the minimum requirement and safety factor is the limit beyond which the part will fail. At the minimum, the safety factor can be equal to the design factor.

11. The margin of safety is the measure of excess structural capability. It is the additional load beyond the design load after which the part fails. If the margin of safety is 0, then the product will fail when it reaches its design load. If the margin of safety is 1, then the part can withstand load more than its design load. And if the margin of safety is -1, then the part will fail even before reaching its design load. MARGIN OF SAFETY Margin of Safety = ( Failure load / Design load )-1 OR = Factor Of Safety-1

12. EXAMPLE

13. We just can not compromise on the factor of safety. Because it affects the product and users who use that product. Having said that we also should not do over-engineering which eventually increases the product cost. We need to find an optimal value of the factor of safety to design a great product. CONCLUSION

14. Thank you! Let me know if you have questions or clarifications.