# FRACTURE MECHANICS & FINITE ELEMENT ANALYSIS - 2017/8

Module code: ENGM250

Module provider

Mechanical Engineering Sciences

Module Leader

OGIN SL Prof (Mech Eng Sci)

Number of Credits

15

ECT Credits

7.5

Framework

FHEQ Level 7

JACs code

H210

Module cap (Maximum number of students)

N/A

Module Availability

Semester 1

Overall student workload

Independent Study Hours: 106

Lecture Hours: 34

Tutorial Hours: 10

Assessment pattern

Assessment type | Unit of assessment | Weighting |
---|---|---|

Examination | EXAMINATION (2 HOURS) | 70% |

Coursework | COURSEWORK (FRACTURE MECHANICS) | 20% |

School-timetabled exam/test | IN-SEMESTER TEST (FINITE ELEMENT ANALYSIS) | 10% |

Alternative Assessment

For the class test element, coursework will be an alternative assessment.

Prerequisites / Co-requisites

Completion of FHEQ Levels 4-6 on an MES UG Programme

Module overview

The module covers the principles of linear elastic and elastic plastic fracture mechanics and their application to predicting the performance of different materials and associated structural components under short-term and long term loading. Further the concepts and principles underlying finite element stress analysis and its application are presented.

Module aims

To review 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) and to explain the relevance of these parameters to different engineering materials.

To demonstrate the range of failure mechanisms that can be shown by the various classes of engineering materials as a function of stress and temperature

To describe the phenomena associated with fatigue deformation and crack growth together with the empirical equations that have been used to quantify these processes.

To provide an understanding of finite element stress analysis enabling the student to appreciate the inherent approximate nature of the technique and the principles that underpin all modern FEA software packages.

Learning outcomes

Attributes Developed | |
---|---|

Identify when the application of linear-elastic fracture mechanics methods is relevant for a simple component. | C |

Identify when the application of elastic-plastic fracture mechanics methods is relevant for a simple component. | C |

Describe the deformation and fracture characteristics of different materials, with reference to the associated material property data. | C |

Make appropriate calculations using these data. | C |

Explain how the finite element method works. | C |

Carry out simple FE calculations by hand. | C |

Attributes Developed

**C** - Cognitive/analytical

**K** - Subject knowledge

**T** - Transferable skills

**P** - Professional/Practical skills

Module content

Indicative content includes:

a) Fracture Mechanics

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) for prediction of 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.

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. Ductile brittle transition in un-notched bars. Cleavage failure.

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.

b) Finite Element Analysis

Finite element principles: Outline of FE method, shape functions, element and global stiffness matrix, a simple example

1D FEA: Bars and beams, shape functions and elements stiffness matrix, assembling and solving the global stiffness matrix

2D FEA: 3-noded triangular element, shape function and element stiffness matrix, 4-noded iso-parametric element, shape functions, Jacobian, element stiffness matrix, numerical integration and solution.

Modal Analysis using FEA: Introduction to dynamics in FEA and simple modal analysis of linear elastic structures.

Methods of Teaching / Learning

The learning and teaching strategy is designed to:

Introduce the principles of linear elastic and elastic-plastic fracture mechanics and to explain their relevance to solving engineering problems relating to crack propagation in structures under short-term and long term (fatigue, creep) conditions. In doing this, the full range of engineering materials will be considered

Introduce the student to the theorem of stationary energy, the role of shape functions and their application to a range of finite elements.

These strategic aims are achieved through lectures that present the underlying theory, worked examples that illustrate the application of this theory and tutorial sessions where students can develop and enhance their understanding of the subject.

The learning and teaching methods include:

Lectures (30 hours, 3 hours/ week for 9 weeks: 15 Fracture mechanics, 12 FEA)

Tutorials (10 hours, 1 hour/week for 10 weeks: 6 Fracture Mechanics, 4 FEA )

Revision lectures (4 hours)

Assessment Strategy

The assessment strategy is designed to provide students with the opportunity: (i) to show an understanding of the properties of the main classes of engineering materials and the principles of fracture mechanics and then apply this knowledge to a range of engineering problems (ii) to demonstrate understanding of the underlying principles of the finite element method and an ability to apply these principles to solve simple finite element problems by hand.

Thus, the summative assessment for this module consists of:

Written examination (2 hours) [Learning Outcomes 1 - 6] {70%}

coursework comprising 2 elements as below:

Class test in FEA, at end of relevant sessions [Learning Outcome 6] {10%}

Fracture mechanics coursework:

LEFM [Learning Outcomes 1, 3, 4] {10%}

EPFM + Fatigue [Learning Outcomes 2 – 4] {10%}

Formative assessment and feedback

Formative assesment and feedback is provided by the weekly supported tutorial work – students complete a set of worked solutions to a range of questions in the tutorial classes and are provided with tutor support in comment and feedback in the sessions. Fully marked and commented coursework and class tests scripts are returned to the students and further feedback is provided through an in-class summary.

Reading list

Reading list for FRACTURE MECHANICS & FINITE ELEMENT ANALYSIS : http://aspire.surrey.ac.uk/modules/engm250

Please note that the information detailed within this record is accurate at the time of publishing and may be subject to change. This record contains information for the most up to date version of the programme / module for the 2017/8 academic year.