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Prof T W Clyne

This course covers various aspects of the performance and usage of composite materials. It is primarily oriented towards "conventional" composites, which comprise long fibres (usually of glass or carbon) in a polymeric matrix. However, there is some coverage of other types of reinforcement and also of composites based on metals or ceramics. The treatment includes both elastic and plastic deformation, plus fracture characteristics, and indications are given as to how composites can often offer highly attractive combinations of lightness, stiffness, strength and toughness, and hence why their usage continues to expand. Certain thermal characteristics are also covered. Towards the end of the course, information is provided about the mechanics of (thick and thin) surface coatings, which can be treated as a special type of composite system.

This lecture course will cover:

  • Overview of Types of Composite System. Overview of composites usage. Types of reinforcement and matrix. Carbon and glass fibres. PMCs, MMCs and CMCs. Aligned fibre composites, woven rovings, chopped strand mat, laminae and laminates.
  • Elastic Properties of Long Fibre Composites. Use of the Slab Model. Halpin-Tsai expressions. Poisson ratios. Elastic loading of a lamina. Matrix notation. Kirchoff assumptions. Axial and transverse loading. Effect of material symmetry on the number of independent elastic constants.
  • Off-axis Elastic Properties of Laminae & Laminates. Loading at an arbitrary angle to the fibre axis. Derivation of transformed stress-strain relationship. Effect of loading angle on stiffness and Poisson ratio. Tensile-shear interaction behaviour. Obtaining the elastic constants of a laminate.
  • Classification of Laminates. Stiffness of laminates. Tensile-shear interactions and balanced laminates. In-plane stresses within a loaded laminate. Coupling stresses and symmetric laminates.
  • Short Fibre & Particulate Composites – Stress Distributions. The Shear Lag Model for stress transfer. Interfacial shear stresses. The stress transfer aspect ratio. Stress distributions with low reinforcement aspect ratios. Numerical model predictions. Hydrostatic stresses and cavitation.
  • Short Fibre & Particulate Composites – Stiffness & Inelastic Behaviour. Load partitioning and stiffness prediction for the Shear Lag model. Fibre aspect ratios needed to approach the long fibre (equal strain) stiffness. Inelastic interfacial phenomena. Interfacial sliding and matrix yielding. Critical aspect ratio for fibre fracture.
  • The Fibre-Matrix Interface. Interfacial bonding mechanisms. Measurement of bond strength. Pull-out & push-out testing. Control of bond strength. Silane coupling agents. Interfacial reactions and their control during processing.
  • Fracture Strength of Composites. Axial tensile strength of long fibre composites. Transverse and shear strength. Mixed mode failure and the Tsai-Hill criterion. Failure of laminates. Internal stresses in laminates. Failure sequences. Testing of tubes in combined tension and torsion.
  • Fracture Toughness of Composites. Energies absorbed by crack deflection and by fibre pull-out. Crack deflection. Toughness of different types of composite. Constraints on matrix plasticity in MMCs. Metal fibre reinforced ceramics.
  • Compressive Loading of Fibre Composites. Modes of failure in compression. Kink band formation. The Argon equation. Prediction of compressive strength and the effect of fibre waviness. Failure in highly aligned systems. Possibility of fibre crushing failure.
  • Thermal Expansion of Composites and Thermal Residual Stresses. Thermal expansivity of long fibre composites. Transverse expansivities. Short fibre and particulate systems. Differential thermal contraction stresses. Thermal cycling. Thermal residual stresses.
  • Surface Coatings as Composite Systems. Misfit strains in substrate-coating systems. Force and moment balances. Relationship between residual stress distribution and system curvature. Curvature measurement to obtain stresses in coatings. Limitations of Stoney equation. Sources of misfit strain. Driving forces for interfacial debonding.