Course Modules - Failure of Materials and Structures

Module Leader

Professor Phil Irving

 

Aim

To provide an understanding why materials and structures fail and how failure conditions can be predicted in metallic and non metallic components and structures.

Syllabus

  • General introduction Over view of failure behaviour of cracked bodies; the influence of crack size, brittle behaviour; ductile behaviour; influence of material properties; cyclic loading and chemical environment
  • Energy approaches to fracture Thermodynamic criteria and energy balance- Griffith approach - application to glass- modifications by Orowan. Strain energy release rate. Compliance. Applications to fibre composites. Stress requirements for fracture; The work of Inglis, Airy and Westergaard
  • LEFM and crack tip stress fields Crack tip stress fields and LEFM, Stress intensity factors and their relation to strain energy release rate; crack tip plasticity, plane stress and plane strain; Constraint; Conditions for validity of LEFM and equivalence of G and K; Fracture toughness in metallic materials; fracture toughness testing; calculations of critical defect sizes and failure stress. Stress concentration at crack tip
  • Beyond the limits of LEFM Crack tip plastic zones - modification of the stress fields. Plane stress and the R curve; The HRR field; CTOD, J; elastic- plastic failure criteria; Defect assessment failure assessment diagrams
  • Polymer composites Return to application of fracture mechanics to polymer composites- use of small specimen data in composite structures
  • LEFM and fatigue crack growth Crack extension under cyclic loading; the Paris law;Regimes of fatigue crack growth; Influence of material properties; crack tip plastic zones in fatigue; Calculation of crack growth life and defect assessment in fatigue;Crack closure and variable amplitude loading; Short cracks and the limits of LEFM; Software Design tools for fatigue crack growth
  • LEFM and chemical environments- static loading-stress corrosion cracking; cyclic loading and corrosion fatigue

Intended Learning Outcomes

On successful completion of this module the student will:

  1. Be familiar with the different regimes and processes of failure of cracked bodies and to understand the factors controlling them and the boundaries and limits between them
  2. Know and understand the principles of linear elastic fracture mechanics (LEFM) and their application to cracks in brittle, ductile and fibre composite materials in. calculation of static failure conditions
  3. Be able to calculate the limits of applicability of LEFM and to apply modified predictive tools such as elastic-plastic fracture mechanics for calculation of failure conditions
  4. Know and to apply fracture mechanics to failure of cracked bodies under cyclic loads and under aggressive chemical environments to predict service lives
  5. Be able to generate laboratory fracture mechanics data; to be able to critically assess its validity for application to particular engineering situations