Fibre reinforced polymeric composites are gradually replacing traditional metal alloys in making primary load carrying structures in aerospace and automobile sector. This is due to their superior structural and functional properties. However, failure of composites under mechanical loading are far more complex than metals. This course would start by highlighting the importance of carrying out failure analysis in composite structures. Next, it would discuss the different failure mechanisms experimentally observed, and introduce several physically based advanced failure theories developed for composites. This course would also cover computational implementation of different failure models as user defined subroutines in a commercial finite element programme.
Introduction to composite materials [5 lectures]
- Composite materials and their internal architecture, advantage as structural material, 3D orthotropic constitutive matrix, uni and multidirectional laminates, lamination theory.
Intra and inter-laminar damage in composites [5 lectures]
- Recapitulation of fracture mechanics, delamination, matrix cracking, fractographic observations, fibre compressive failure, fibre tensile failure, dynamic loading and impact damage, benchmark experiments to extract fracture parameters, laminate size effect on failure, effect of manufacturing induced defects on failure.
Modelling delamination and Matrix cracking [5 lectures]
- Concept of quasi-brittle material and origin of cohesive zone model, adaptation to composites delamination and matrix cracking, different onset and propagation criteria, development of 3D mixed mode bilinear cohesive constitutive law, virtual crack closure technique (VCCT), analytical models for residual strength prediction.
Fibre tensile and fibre compressive failure [3 lectures]
- Onset strength and Weibull statistical theory for fibre tensile failure, fibre microbuckling and fibre kinking failure theories under compression, influence of shear nonlinearity.
Essentials of continuum mechanics [5 lectures]
- Deformation, strain and stress measures, large deformation and objective stress rates.
Essentials of continuum damage mechanics [4 lectures]
- Idea of continuum damage, strain equivalence principle, thermodynamic basis of continuum damage.
Finite element modelling framework for damage [5 lectures]
- Governing equation for dynamic equilibrium, weak form for a body including cracks, finite element discretisation, formulation 3D isoparametric finite elements, dynamic explicit finite element method.
Implementation of damage models in finite element framework [8 lectures]
- Implementation of damage models in commercial finite element software in the form of user-defined materials and user-defined elements, several aspects of modelling, interpretation of results.
Post-Graduate students (Open Elective)
Outcomes of this Course
On completion of this course, students would be able to:
- Appreciate the use of carbon fibre composites in structural engineering.
- Be familiar with the internal architecture of fibre reinforced composites, design of multidirectional laminates, lamination theory .
- Know about strength of a lamina and laminate, potential weak regions in a laminate, different mechanisms of laminate failure.
- Know about several phenomenological and physically based failure theories developed for composites.
- Learn basics of continuum damage mechanics and numerical implementation.
- Carry out computer simulation of progressive failure in composite structures using commercially available finite element package.