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MODERATELY DUCTILE FAILURE

MODERATELY DUCTILE FAILURE

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MODERATELY DUCTILE FAILURE

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  1. MODERATELY DUCTILE FAILURE • Evolution to failure: 50 mm 50 mm • Resulting fracture surfaces (steel) 100 mm particles serve as void nucleation sites. 4

  2. IDEAL VS REAL MATERIALS TS << TS engineering materials perfect materials • Stress-strain behavior (Room T): • DaVinci (500 yrs ago!) observed... --the longer the wire, the smaller the load to fail it. • Reasons: --flaws cause premature failure. --Larger samples are more flawed! 6

  3. LOADING RATE • Increased loading rate... --increases sy and TS --decreases %EL • Why? An increased rate gives less time for disl. to move past obstacles. • Impact loading: --severe testing case --more brittle --smaller toughness 14

  4. TEMPERATURE • Increasing temperature... --increases %EL and Kc • Ductile-to-brittle transition temperature (DBTT)... 15

  5. DESIGN STRATEGY:STAY ABOVE THE DBTT! • Pre-WWII: The Titanic • WWII: Liberty ships • Problem: Used a type of steel with a DBTT ~ Room temp. 16