3.11 MECHANICS OF MATERIALS F03Lecture #34Professor Christine OrtizOFFICE : 13-4022 PHONE : 452-3084WWW : http://web.mit.edu/cortiz/wwwFRACTURE MECHANICS IInstrumented Impact TestsFRACTURE : BASIC DEFINITIONSFRACTURE : BASIC DEFINITIONSDependence on MicrostructureExamplesLiberty Ships-World War II• The hulls of Liberty Ships fractured without warning, mainly in the North Atlantic.• There were 2,751 Liberty Ships manufactured between 1941-1945. 30% suffered catastrophic failures; only 2 exist today which are sea-worthy.ExamplesLiberty Ships-World War II•the all-welded construction which eliminated crack-arresting plate boundaries which are present in riveted joints •the presence of crack- like flaws in welded joints performed by inexperienced operators pressed into service by the exigencies of the programme•use of materials whose low resistance to crack advance ( toughness ) was further reduced by low temperatures in the North Atlantic (low quality steel)ExamplesThe Aloha Boeing 737 AccidentOn April 28, 1988, part of the fuselage of a Boeing 737 failed after 19 years of service. The failure was caused by fatigue (multi-site damage).THEORETICAL CLEAVAGE STRESSTHEORETICAL CLEAVAGE STRESSσrereλ/2FRACTURE STRESSStress Concentrationhttp://www.mrl.ucsb.edu/~edkramer/LectureVGsMat100B/99Lecture21VGs/StressConcentrationVG.htmlMaterials in Principle and PracticeStress ConcentrationEXPERIMENTAL FRACTURE STRESSResults of Griffiths Experiments on Glass
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