Materials Under Stress

Module summary

Module code: MECH1026
Level: 6
Credits: 15
School: Engineering and Science
Department: Engineering
Module Coordinator(s): Mark Bingley

Specification

Aims

To provide the student with the tools for analysis of ductile, brittle and fatigue fracture processes. To assist the student in the recognition of various failure modes, and to explore procedures for evaluation these. To enhance their understanding of the mechanical properties of the various classes of material.

Learning outcomes

On successful completion of this course a student will be able to:
1: Identify, and relate to the underlying mechanisms, a range of materials failure modes.
2: Understand the factors influencing the occurrence of various types of fracture and devise the solutions to mitigate them.
3: Critically analyse information and data to plan and implement a solution to an engineering problem.
4: Draw robust conclusions from experimental results and interpret and explain them with respect to accepted theory.

Indicative content

Fracture and Fracture Mechanics:
Materials Failure: modes of failure, failure mechanisms for metals, ceramics and polymers, fracture surfaces and the interpretation of features.

Stress Concentrations: stress concentration factors.

Fracture Mechanics: Griffiths energy criteria for failure; stress analysis of cracks; stress intensity factors; Y-calibration factors for different shaped flaws; crack tip plasticity; plasticity correction factors; plane strain and plain stress failure.

Fracture toughness testing: plane strain fracture toughness testing; crack opening displacement; toughness of ceramics.

Transition Temperature approach to fracture control: impact energy; transition temperature in steels; impact energy-fracture toughness correlations.

Statistical nature of fracture: Weibull analysis.

Macroscopic and microscopic examination of fracture surfaces: case studies of failures; improving the toughness of materials; metals, ceramics, polymers.

Thermal stresses and thermal shock failure.

Environmental assisted cracking.


Fatigue:
Introduction to fatigue: occurrences of fatigue; macroscopic and microscopic features of fatigue fracture surfaces

Measuring fatigue: S-N curves; fatige life; fatigue limit and fatigue stress; effect of mean stress on fatigue life; Palgrem and Miner cumulative damage law.

High and low cycle fatigue: stress and strain controlled fatigue; cyclic softening and cyclic hardening; Basquins Law and Coffin-Manson relationships.

Fatigue crack growth: microstructural short crack regime; physically short crack regime; LEFM long crack regime; Paris Law equation; effect of mean stress; effect of grain size, effect of corrosive environments.

Notch effects and fatigue initiation: stress concentration effects; notch sensitivity factor; fatigue notch factor.

Fatigue of welds:

Fatigue of polymers: effect of loading frequency; effect of surface treatments.

Design against fatigue failure: materials selection; metallurgical treatments; reduction of stress concentrations; surface finishing.

Teaching and learning activity

The course will be taught by the following learning mechanisms:

Formal lectures, Tutorials + problem solving classes, Laboratory practicals and case studies.

Assessment

Students are required to pass all components in order to pass the course. As part of the requirement, each component must be passed with the minimum pass mark as detailed below. The course must be passed with an overall minimum of 40%.

Methods of SUMMATIVE Assessment: Continuous Assessment.
Nature of FORMATIVE assessment supporting student learning: Observations, Questioning Discussion, Constructive Quizzes.
Outcome(s) assessed by summative assessment (Please use the numbers above to refer to these): 1, 2, 3, 4.
Grading Mode: Numeric.
Weighting: 30%.
Pass Mark: 30%.
Outline Details: Laboratory Reports, Case studies, Independent research.

Methods of SUMMATIVE Assessment: Examination.
Nature of FORMATIVE assessment supporting student learning: Practice Exam Papers.
Outcome(s) assessed by summative assessment (Please use the numbers above to refer to these): 1, 2, 3.
Grading Mode: Numeric.
Weighting: 70%.
Pass Mark: 30%.
Outline Details: 3 Hour Closed-Book Exam.