Board of European Students of Technology BEST Symposium on Education

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An example of students projects the Fracture
Mechanics course of the Mech. Engng. degree of
FEUP (presentation at BEST Symposium on
Education, FEUP, May 2, 2006) Fracture Mechs.
is an optional course of the 5th (and final) year
of the Mech. Engng. degree, 2nd semestre
2005/2006 The course seeks to provide knowledge
of methods of design for fracture avoidance,
evaluation of structural integrity, and failure
analysis Students attend lectures and work
autonomously on several computational modelling
assignments suggested by the teacher Prof Paulo
M S Tavares de Castro This example concerns work
carried out in the first part of the course by
Ricardo D Pedrosa (March/April 2006)
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Why the course ? a few examples of well known
cases (taken, for this presentation, from the
aeronautics area) Comet accidents in early
fifties
after several catastrophic accidents Comet was
taken from commercial use testing revealed that
these planes had a major fatigue weakness ... the
designers insisted on square windows
... http//www.tech.plym.ac.uk/sme/Interactive_Res
ources/tutorials/FailureCases/sf2.html
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wreckage of the fuselage of the Comet the
primary cracks are shown propagating well beyond
the fastener lines of several fuselage frames,
without arrest
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But also more recent Aloha flight 243, Boeing
737, 1988 the aircraft lost 1/3 of its roof while
cruising at 24,000 feet. One flight attendant was
sucked from the airplane, which subsequently made
a safe emergency landing
http//www.facstaff.bucknell.edu/rich/MECH353/TN35
3A2.htm
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The assignment study of deformation of a cracked
body subjected to tensile loads characterization
of the stress field at the crack tip 3 cases
were studied
case 1 (left) quarter of plate, remotely loaded
by uniform tensile stress s crack length
2a case 2 (right) half plate, remotely loaded
by uniform tensile stress s crack length a
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cases 1 and 2 finite element mesh ANSYS
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cases 1 and 2 detail of finite element mesh
crack tip region
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Deformed Plates
case 1, central crack
case 2, lateral crack
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?y stress
case 2, lateral crack
case 1, central crack
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theoretical result for the crack deformation of
case 1
Error
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Case 1 Central Crack
stress intensity factor KI for case 1, using the
nodal forces method
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Case 2 Lateral Crack
stress intensity factor KI for case 2, using the
nodal forces method
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case 3 plate subjected to remote tensile
stress s, with a cracked hole verification of
the approximate solution
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case 3 finite element mesh ANSYS
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Detail of finite element mesh Crack tip region
Deformed Plate
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sy
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stress intensity factor KI for case 3, using the
nodal forces method
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case 3 plate subjected to remote tensile
stress s. The stress intensity factor for cracks
propagating from opposite sides of an open hole
in an infinite plate can be writen as
Source D. S. Dawicke and J. C. Newman, Jr.
Analysis and prediction of multiple-site damage
(MSD) fatigue crack growth, NASA TP 3231,
1992 http//hdl.handle.net/2002/12177
http//library-dspace.larc.nasa.gov/dspace/jsp/b
itstream/2002/12177/1/tp3231.pdf
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• With project work such as this, it is intended
  to
• motivate students to deeper learning of the
  subject
• contribute to students autonomy
• acquaint students with advanced tools
• train students to research data, bibliography,
  analytical and numerical tools,
• develop technical report writting, and
  communication skills.