3 11 MECHANICS OF MATERIALS F03 Lecture 34 Professor Christine Ortiz OFFICE 13 4022 PHONE 452 3084 WWW http web mit edu cortiz www FRACTURE MECHANICS I Instrumented Impact Tests FRACTURE BASIC DEFINITIONS FRACTURE BASIC DEFINITIONS Dependence on Microstructure Examples Liberty 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 Examples Liberty 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 Examples The Aloha Boeing 737 Accident On 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 STRESS THEORETICAL CLEAVAGE STRESS re re 2 FRACTURE STRESS Stress Concentration http www mrl ucsb edu edkramer LectureVGsMat100B 99Lecture21VGs StressConcentrationVG html Stress Concentration Materials in Principle and Practice EXPERIMENTAL FRACTURE STRESS Results of Griffiths Experiments on Glass Fibers http www umr edu dharani FractureMechanics Lesson 2 ppt
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