Matrix-Fiber Adhesion of Fiber Reinforced Composites

1. Matrix-Fiber Adhesion of Fiber Reinforced Composites Robert Peterson Material Science II Spring 2006

2. Fiber Reinforced Composite Are some of the most commonly used composites in industry Comprised of two phases, the Fibers and the matrix.

3. Fiber Phase By itself it is very weak and brittle Has a high tensile strength and even higher Modulus of Elasticity Small fibers are much stronger than bulk ones Whiskers, Fibers, and Metallic Wires

4. Matrix Phase Binds together fibers, and acts as the medium for external stress to be applied through the fibers Only a small amount of the load is supported by the matrix phase and the elastic modulus of the fibers should be much higher than that of the matrix

5. Matrix Phase Cont. Being softer and more ductile than the fiber phase, it is used to add fracture toughness and prevent propagation of cracks. and protect fibers from abrasion, environmental or chemical reactions Bonding force is critical to the prevention of fiber pullout. The matrix needs to be chosen to fit the conditions of the environment that it will be located in.

6. Properties for Strong Fiber-Matrix Adhesion Strong chemical bonding interaction with fiber an matrix is required to prevent fiber pullout Polar bonding is often desired for finding optimum bonding strength in fiber reinforced composites Round fibers produce a stronger and more uniform bond with its matrix. Edges in fibers result in stress concentrations

7. Properties for Strong Fiber-Matrix Adhesion When making a composite the fibers must be wetted for strong bonding to occur, or a wetting agent added to promote adhesion Chemical reaction between fiber and matrix also promotes stronger bonding but can also weaken the fiber structure

8. Strength of Carbon Fiber Composites Low bonding strength between carbon fiber and matrix results in failure in pure shear If the bonding strength between carbon fiber and its matrix is too strong, it will result in a brittle structure Treatment and size of fibers used in carbon fiber is critical to achieving its optimum strength and bonding characteristics Strong Carbon fiber composites will fail in mixed modes of fracture

9. Strength of Carbon Fiber Composites Weave patterns also play a critical role in strength of carbon composites 8H satin weave creates a denser, composite with more homogenous matrix dispersion This densification results in a increased flexural strength of the composite

10. Designing Composites for Their Operational Environment Catastrophic failure of fiber reinforced composites will occur if they are not designed to their environment The matrix phase is most important component to consider for serviceability The matrix will start flowing at temperature long before the fiber phase will typically start degrading The matrix should also re resistant to any chemicals it may contact in its operational environment

11. Designing Composites for Their Operational Environment The application of use for a composite is also should be considered when designing a composite