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ME 418 L AB D1 F ATIGUE TESTING Unyime (Uy) Bassey Umoh address – Office # - 1B70 September 2013

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O BJECTIVES 1. To understand the fatigue behaviour of 1018 steel 2. To understand treatments to improve the fatigue strength of 1018 steel 3. To understand the operation of 4 fatigue machines Krouse RR. Moore Budd Warner-Swasey 4. To complete 2 fatigue tests on a standard specimen using a Krouse rotating beam machine Without treatment With treatment 2 ME 418 Lab D

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L ABORATORY T IMELINE 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 3 ME 418 Lab D

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L OGBOOK 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 4 ME 418 Lab D

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T HEORY – 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 5 ME 418 Lab D

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T HEORY – 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 S f for actual machine part and S f for small polished specimen. 6 ME 418 Lab D

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T HEORY – CONCEPTS 7 ME 418 Lab D Figure 1: S-N curves showing response to cyclic loading SfSf

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T HEORY – 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 S N for actual machine part and S N for small polished specimen 8 ME 418 Lab D

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T HEORY – CONCEPTS 9 ME 418 Lab D Figure 1: S-N curves showing response to cyclic loading N

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T HEORY – CONCEPTS 10 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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T HEORY – EQUATIONS *Logarithmic relationship - A straight line between S 1 and S 10 6 on a semi-log plot (i.e. S N vs. log[N]): S N = 1/6 (S S 1 ).log(N/10 6 ) + S ME 418 Lab D

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T HEORY – EQUATIONS *Power relationship – A straight line between S 10 3 and S 10 6 on a log-log plot (i.e. log[S N ] vs Log[N]): S N = S (N/10 6 ) (-1/3log[S 10 3 /S 10 6 ]) 12 ME 418 Lab D

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T HEORY – EQUATIONS Where: S 1 = S UT S N = ZS UT *S 10 3 = 0.9S UT S 10 6 = S N C L C S C G C T C R and, C L = Load factor C S = Surface factor C G = Gradient factor C T = Temperature factor C R = Reliability factor S N = Endurance limit for a mirror polished specimen Z = Endurance ratio (Estimated as 0.5)* 13 ME 418 Lab D

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L OGBOOK 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 14 ME 418 Lab D

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CALCULATIONS (P OWER RELATIONSHIP ) Determine: 1) S N N Group = To be Provided, D Group = To be Measured, and: S UT = 114 ksi C L = 1 C S = 0.74 C G = 1 C T = 1 C R = 1 Z = ME 418 Lab D

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CALCULATIONS 2) Estimated time for test, assuming 5000rpm 3) Moment, M 16 ME 418 Lab D

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L OGBOOK 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 17 ME 418 Lab D

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R ESEARCH C HALLENGE Literature search and Brain storming Treatment of same specimen to Increase fatigue strength showing 1. Specimen treatment Temperature Time 2. Justification Mechanical properties Micro-structural considerations 3. Note references 18 ME 418 Lab D

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A FTER 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 19 ME 418 Lab D

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L OGBOOK 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 20 ME 418 Lab D

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