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Fatigue

Fatigue. Crack Initiation. Crack Propagation. Sudden Fracture. http:// en.wikipedia.org/wiki/File:Pedalarm_Bruch.jpg – image shared under a Creative Commons share-alike License. Models. S-N. e -N. LEFM. Describes crack propagation

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Fatigue

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  1. Fatigue Crack Initiation Crack Propagation Sudden Fracture http://en.wikipedia.org/wiki/File:Pedalarm_Bruch.jpg – image shared under a Creative Commons share-alike License Ohio University - Dr. Cyders

  2. Models S-N e-N LEFM • Describes crack propagation • Predict remaining life in a part (non-destructive testing) • Model based on existing cracks • Models sensitive to accuracy of stress intensity factors • Strain-based • Accurate for crack initiation and damage • Good for LCF • Complicated approach • Requires computational model • Easiest approach • Design for infinite life • M.O.: Prevent crack initiation with strength criterion • Least accurate for LCF • Does not describe crack growth Ohio University - Dr. Cyders

  3. Ohio University - Dr. Cyders

  4. Ohio University - Dr. Cyders

  5. Ohio University - Dr. Cyders

  6. See Norton for theoretical fatigue/endurance strength values • For typical materials, theoretical endurance/fatigue strengths are roughly half the ultimate tensile strength Ohio University - Dr. Cyders

  7. Ohio University - Dr. Cyders

  8. Example – 6061-T6 Ohio University - Dr. Cyders

  9. General Procedure • Select Material • Calculate Sm & Se’ (or Sf’) • Calculate Correction Factors • Calculate Corrected Se(or Sf) • Draw S-N diagram • Calculate sA for desired life • Set acceptable sAwith safety factor Ohio University - Dr. Cyders

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