ME 418 Lab D1 Fatigue testing

1. ME 418 Lab D1 Fatigue testing Unyime (Uy) BasseyUmoh Email address – ubu610@mail.usask.ca Office # - 1B70 September 2012

2. Objectives • To understand the fatigue behaviour of 1018 steel • To understand treatments to improve the fatigue strength of 1018 steel • To understand the operation of 4 fatigue machines • Krouse • RR. Moore • Budd • Warner-Swasey • To complete 2 fatigue tests on a standard specimen using a Krouse rotating beam machine • Without treatment • With treatment ME 418 Lab D1 - 2012

3. Laboratory Timeline • Go through concepts of fatigue and equations • Go through sample calculations • Carry out actual calculations for Krouse test • Observe operation of Krouse machine and carry out test • Observe operation of 4 fatigue testing machines • Carry out research challenge • Record information from Krouse test and sketch sample identifying crack initiation ME 418 Lab D1 - 2012

4. Logbook checklist • Objectives and background information • Sample calculations • Lab calculations • Information for 4 machines • Sketch of Diagrams • Method of loading • Types of stresses produced • Brief description of operation • Experiment • Number of cycles at failure • Sketch of failed specimen • Treatment • Procedure • Justification, and • References • Future discussion points ME 418 Lab D1 - 2012

5. Theory – concepts • Fatigue Failure: Progressive Failure process of a material due to repeated cyclic loading. Loading induces cyclic stresses, which initiates cracks and cause them to be propagated until failure occurs (Collins 43) • Stress-time patterns • Completely reversed (Zero-mean) cyclic stresses* • Nonzero-mean cyclic stresses • Random stresses ME 418 Lab D1 - 2012

6. Theory – concepts • Fatigue (endurance) Limit: The stress level under which an infinite number of cycles can be sustained without failure of the material. • Response of Ferrous materials and Titanium • Denoted as Sf for actual machine part and Sf’ for small polished specimen. ME 418 Lab D1 - 2012

7. Theory – concepts Sf ME 418 Lab D1 - 2012 Figure 1: S-N curves showing response to cyclic loading http://www.efunda.com/formulae/solid_mechanics/fatigue/images/fatigue_SN_01.gif

8. Theory – concepts • Fatigue strength: The stress level at which a material will fail when loaded by N number of cycles. • Response of Non-ferrous materials • Denoted as SN for actual machine part and SN’ for small polished specimen ME 418 Lab D1 - 2012

9. Theory – concepts ME 418 Lab D1 - 2012 SN N Figure 1: S-N curves showing response to cyclic loading http://www.efunda.com/formulae/solid_mechanics/fatigue/images/fatigue_SN_01.gif

10. Theory – concepts ME 418 Lab D1 - 2012 Figure 1: S-N curves for Ferrous and non-ferrous materials (Taken without permission from Collins, J. A. Mechanical Design of Machine Elements and Machines: a Failure Prevention Perspective. New York, NY: Wiley, 2003. Print)

11. Theory – equations • *Logarithmic relationship - A straight line between S1and S106 on a semi-log plot (i.e. SN vs. log[N]): SN = 1/6 (S106 - S1).log(N/106) + S106 ME 418 Lab D1 - 2012

12. Theory – equations • *Power relationship – A straight line between S103 and S106 on a log-log plot (i.e. log[SN] vs Log[N]): SN = S106 . (N/106)(-1/3log[S103/S106]) ME 418 Lab D1 - 2012

13. Theory – equations Where: S1 = SUT SN’ = ZSUT *S103 = 0.9SUT S106 = SN’CLCSCGCT CR and, CL = Load factor CS = Surface factor CG = Gradient factor CT = Temperature factor CR = Reliability factor SN’ = Endurance limit for a mirror polished specimen Z= Endurance ratio (Estimated as 0.5)* ME 418 Lab D1 - 2012

14. Sample calculation (Power relationship) Determine SN when N = 20,000 cycles Given that: SUT = 114 ksi CL = 1 CS = 0.74 CG = 1 CT = 1 CR = 1 Z = 0.5 ME 418 Lab D1 - 2012

15. Actual calculations • N given • D measured • Determine: • SN • Estimated time for test, assuming 5000rpm • M ME 418 Lab D1 - 2012

16. Logbook checklist • Objectives and background information • Sample calculations • Lab calculations • Information for 4 machines (Excluding M.T.S.) • Sketch of Diagrams • Method of loading • Types of stresses produced • Brief description of operation • Experiment • Number of cycles at failure • Sketch of failed specimen • Treatment • Procedure • Justification, and • References • Future discussion points ME 418 Lab D1 - 2012

17. Research Challenge • Literature search and Brain storming • Treatment of same specimen to Increase fatigue strength showing • Specimen treatment • Temperature • Time • Justification • Mechanical properties • Micro-structural considerations • Note references ME 418 Lab D1 - 2012

18. After lab to do • Treatment • Submit treatment procedure within 2 school days • Complete treatment within 1 week of acceptance • Submit specimen according to schedule posted in 2C26 • Email Rob peace – rob.peace@usask.ca • Include all treatment results that will be sent out in your logbook • Compare strength of heat treated sample with non-heat treated sample • Plot S-N relationship from all groups data • Assuming power relationship, determine experimental endurance ratio and ultimate strength of the steel • Compare S-N for theoretical and experimental ME 418 Lab D1 - 2012

19. Logbook checklist • Objectives and background information • Sample calculations • Lab calculations • Information for 4 machines (Excluding M.T.S.) • Sketch of Diagrams • Method of loading • Types of stresses produced • Brief description of operation • Experiment • Number of cycles at failure • Sketch of failed specimen • Treatment • Procedure • Justification, and • References • Future discussion points ME 418 Lab D1 - 2012