COMPOSITE_MATERIALS_module_4_INTERFACE_b

COMPOSITE_MATERIALS_module_4_INTERFACE_b - 1 ME 624:...

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Unformatted text preview: 1 ME 624: MECHANICS OF COMPOSITE MATERIALS Module 4: The Matrix / Fiber Interface (Material Based on: Composite Materials by Matthews & Rawlings and other References) 2 atrix / Fiber Interface : efinitions The interface between any two phases (fiber and matrix, for example) is the region through which material parameters such as element concentration, crystal structure, and other mechanical and physical properties change from one phase to another. In some situations, the width of the interface is no thicker than a few atoms while in other cases the interface witnesses extensive inter-diffusion resulting in a distinct ‘hybrid’ phase and may be recognized as an ‘ inter-phase’ . articularly in the case of polymer-matrix composites, an intimate contact at the molecular level between the fiber and the matrix brings intermolecular forces to play (with or without causing a chemical linkage between the components). This intimate contact requires that the matrix (in the liquid form) must wet the fiber. Wetting is particularly important for the pick up of resin by fiber tows and the impregnation of resin into fiber bundles. 3 atrix / Fiber Interface : rinciple ettability Æ Intimate Contact Æ Bonding Æ Adhesion Strength 4 . Wettability 5 atrix / Fiber Interface : ettability sound composite is one that has a sound matrix-fiber interface. The quality of this interface is measured by the strength of adhesion across that interface. Interfacial bonding is necessary for the integrity of the composite system as a whole. The adhesion between the reinforcing fiber and the matrix is what guarantees the load transfer between these two components. For adhesion to occur, the fiber and the matrix must be brought into intimate contact during matrix fabrication. Therefore, wettability defines the extent to which a liquid will spread over a solid surface. Good wettability means that the liquid (matrix) will flow over the reinforcement covering every bump and dip of the rough surface of the reinforcement and displacing all air. 6 atrix / Fiber Interface : ettability Take for example a liquid drop ( simulates the liquid matrix ) on a solid surface (simulates the fiber). The surface energy per unit area of the solid-gas, liquid-gas, and solid-liquid interfaces are , respectively. SL LG SG γ γ γ , , The liquid drop will spread only if this results in a net drop in the total energy of the system. (Note that a portion of the solid-vapor (same as solid-gas) interface was replaced by a solid-liquid interface). Therefore, the condition for wettability is SG LG SL γ γ γ < + where the substitution of the solid-gas interface favors the reduction of the system’s energy . 7 atrix / Fiber Interface : ettability This implies that a liquid resin with a certain free surface energy is not capable of wetting a fiber of lower free surface energy . Note that the free energy of an interface is measured in units of J/m2 and can be shown to be equal to the surface tension of which has a unit of force per unit...
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This note was uploaded on 02/07/2011 for the course MECH 624 taught by Professor Drramseyhamade during the Fall '10 term at American University of Beirut.

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COMPOSITE_MATERIALS_module_4_INTERFACE_b - 1 ME 624:...

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