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| Module Availability |
| Autumn Semester |
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| Assessment Pattern |
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Components of Assessment
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Method(s)
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Weighting
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Examination
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2-hour paper
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70%
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Coursework
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3 assignments
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30%
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| Module Overview |
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| Prerequisites/Co-requisites |
A final year module suitable for aerospace, mechanical and medical engineering students.
Completion of the progress requirements of Level HE2 |
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| Module Aims |
Aims
The theoretical background to the key linear elastic fracture mechanics parameters (stress intensity factory, strain energy release rate) and elastic/plastic fracture mechanics parameters (crack opening displacement, J-integral) will be reviewed. The relevance of these parameters to different engineering materials will be explained. Fatigue deformation and crack growth phenomena will be described along with the empirical equations that have been used to quantify these processes. |
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| Learning Outcomes |
Intended learning outcomes
Students will be able to (i) recognise situations in which fracture mechanics is relevant for a simple component, (ii) understand the deformation and fracture characteristics of different materials and the associated material property data (iii) make appropriate simple calculations using these data and (iv) appreciate the limitations of these calculations. |
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| Module Content |
Competition between yield and fracture under plane-stress/plane-strain conditions. Ideal strength of a material. Effect of stress concentrators and cracks.
The use of the stress intensity factor to characterise near-crack-tip stress fields leading to a material property (fracture toughness) controlling crack propagation. Expressions for stress intensity factors for a range of geometries.
Modes of crack tip opening and corresponding stress intensity factors/crack tip stress fields. Mixed mode fracture problems. Failure of brittle solids in compression.
Griffith energy balance analysis and its relation to stress intensity approach. Linear elastic fracture mechanics (LEFM). Limitations of LEFM - role of crack tip plasticity. The 'thickness' criterion for plane strain conditions to apply. Measurement of fracture toughness.
Crack-opening displacement approach to fracture. Derivation of expression for COD and compatibility with LEFM. COD-based design curves.
J Integral approach to fracture. Definition, measurement and calculation from computer-based stress analysis including ideas of path-independence. Applications.
Failure by ductile rupture - micro-void initiation, growth and coalescence. Model of Brown and Embury. Ductile brittle transition in un-notched bars. Cleavage failure from dislocation pile-up. Model of Cottrell.
Mechanisms of creep fracture at elevated temperature. Deformation and fracture mechanism maps for metals, ceramics and polymers.
Fatigue failure. Cyclic stress/strain behaviour leading to hardening or softening. Crack initiation and growth mechanisms. Empirical laws for fatigue failure - Coffin-Manson, Basquin, Goodman and Miner. Crack growth (Paris) relation - application and limitations. Crack closure.
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| Methods of Teaching/Learning |
Methods of Teaching/Learning
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18 hrs lectures, 6 hrs tutorials, and 76 hrs independent learning time.
Total student learning time 100 hours.
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Methods of Assessment and Weighting
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Components of Assessment
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Method(s)
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Weighting
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Examination
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2-hour paper
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70%
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Coursework
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4 assignments
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30%
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| Selected Texts/Journals |
recommended texts for reference
Ashby MF and Jones DRH, Engineering Materials 1: An Introduction to their Properties and Applications, Butterworth-Heinemann, 3rd ed, 2005. (ISBN 07506 63804)
Hertzberg RW, Deformation and Fracture Mechanics of Engineering Materials, 4th ed, Wiley, 1996. (ISBN 04710 12149)
Required
Reading
None |
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| Last Updated |
18 September 2008 |
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