MIT2_72s09_lec04

MIT2_72s09_lec04 - MIT OpenCourseWare http://ocw.mit.edu...

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Unformatted text preview: MIT OpenCourseWare http://ocw.mit.edu 2.72 Elements of Mechanical Design Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms . 2.72 Elements of Mechanical Design Lecture 04: Fatigue Schedule and reading assignment Please see unterhausen. "fatigue crack." March 27, 2008. YouTube. Accessed October 28, 2009. http://www.youtube.com/watch?v=iBuuVd0JlIM Reading quiz Announcements Shaft due date Shaft exercise Goodman diagram quiz (Tuesday) Shear-moment qualifying quiz (Tuesday) Topics Discuss stiffness exercises Start fatigue Reading None, for Tuesday, prep for quizzes in lab time (Given lounge, top of 35) Martin Culpepper, All rights reserved 2 Reading quiz Discuss stiffness exercises Answers Intuition about stiffness Part Spindle Carriage-rail Etc Insight and perspective Martin Culpepper, All rights reserved Carriage bearing-rail Combined Stiffness K K/2 K/3 K/4 K/5 0 1 2 3 4 K/K 4 Shaft exercise Are you on top of this!? Fatigue part I At what critical time in engineering history did fatigue became relevant? Why does fatigue failure generate serious concern? What type of warnings does one receive? Fire plane wing failure July 18, 2002 near Estes Park, Colorado Both crew members killed Delivered in July, 1945 to the U.S. Navy Logged 8000+ flight hours Investigation NTSB found extensive fatigue Cracks hidden from view Please see r ichmondlopez13. "Plane crash caught on tape - 6." Martin Culpepper, All rights reserved December 5, 2007. YouTube. Accessed October 14, 2009. http://www.youtube.com/watch?v=j7kr6o1s9sI 10 Comet airplane failures BOAC Flight 781 crashes on 10 January 1954 Concluded fire was most likely cause Resumed on 23 March 1954 Comet G-ALYY crashes on 8 April 1954 Pressure tests revealed fatigue Windows to be glued & riveted, Square windows oval Skin thickened Service in 1958 but riveted only Martin Culpepper, All rights reserved 11 I-35 bridge failure By Laurie Blake, Paul Mcenroe, Pat Doyle and Tony Kennedy, Star Tribune MnDOTs options: Make repairs or find flaws & bolt on steel plating Fueled emotional debate Image from Wikimedia Commons, http://commons.wikimedia.org MNDOTs action: Thousands of bolt holes would weaken bridge Launched inspection, interrupted by work on bridge surface The state's top bridge engineer: "We chose the inspection route.. We thought we had done all we could, but obviously something went terribly wrong." "Up until the late 1960s, it was thought that fatigue was not a phenomenon you would see in bridges. Martin Culpepper, All rights reserved 12 How much do engineers know about fatigue?...
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MIT2_72s09_lec04 - MIT OpenCourseWare http://ocw.mit.edu...

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