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**ME 418 Lab D1 Fatigue testing**

Unyime (Uy) Bassey Umoh address – Office # - 1B70 September 2013

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**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 D

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**Laboratory Timeline Go through concepts of fatigue and equations**

Carry out calculations relevant towards the 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 D

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**Logbook checklist Objectives Background information 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 D

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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 D *Stresses are induced by the loads applied

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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 D

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Theory – concepts Sf ME 418 Lab D Figure 1: S-N curves showing response to cyclic loading

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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 D

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Theory – concepts SN ME 418 Lab D N Figure 1: S-N curves showing response to cyclic loading

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Theory – concepts ME 418 Lab D 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, Print)

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**SN = 1/6 (S106 - S1).log(N/106) + S106 Theory – equations**

*Logarithmic relationship - A straight line between S1 and S106 on a semi-log plot (i.e. SN vs. log[N]): SN = 1/6 (S106 - S1).log(N/106) + S106 ME 418 Lab D * - This relationship can be obtained for the estimation of an S-N Curve for materials, if the curve is assumed to be a straight line in a semi-log plot (i.e. SN vs. log[N]). The resulting equation can be derived on your own based on this estimation. Note that the equation itself is not established in literature, but the approach of estimating the curve as a straight line is established in literature and can be seen in texts. Refer to Chapter 2 of “Mechanical design of machine elements and machines” by Jack Collins to see more about this estimation.

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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 D * Log-log plots for ferrous S-N curves is convenient as it provides a straight line relationship. Again, the equations can be derived based on these straight line relationships. More about this can be seen in Chapter 8 of Juvinall and Marshek 2000.

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**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 D *Equation obtained for S103 and Z seen for rotating bending scenario (See Juvinall and Masherk 2000 for more information). The equations above were obtained based on observation of large amount of empirical data. Also, C factors can be seen in: 1. Juvinal and Marsherk 2000 – Fundamentals of Machine Component Design - Table 8.1, page 316; Figure 8.13 Referred to as Marin factors as seen in: 1. Shigley’s Mechanical Engineering Design 2008 – Pages 2. Jack A. Collins 2003 – Mechanical design of Machine Elements and Machines – Table 2.2 pages ; Figure 2.21 page 53

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**Logbook checklist Objectives Background information 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 D

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**calculations (Power relationship)**

Determine: 1) SN NGroup = To be Provided, DGroup = To be Measured, and: SUT = 114 ksi CL = 1 CS = 0.74 CG = 1 CT = 1 CR = 1 Z = 0.5 ME 418 Lab D

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**calculations 2) Estimated time for test, assuming 5000rpm 3) Moment, M**

ME 418 Lab D

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**Logbook checklist Objectives Background information 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 D

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**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 D

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**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 Rob peace – 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 D

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**Logbook checklist Objectives Background information 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 D

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