Interfaces

Abstract

We can define an interface between a reinforcement and a matrix as the bounding surface between the two across which a discontinuity in some parameter occurs. The discontinuity across the interface may be sharp or gradual. Mathematically, interface is a bidimensional region. In practice, we have an interfacial region with a finite thickness. In any event, an interface is the region through which material parameters, such as concentration of an element, crystal structure, atomic registry, elastic modulus, density, coefficient of thermal expansion, etc., change from one side to another. Clearly, a given interface may involve one or more of these items.

Problems

• 4.1. Describe some techniques for measuring interfacial energies in different composite systems.

• 4.2. In order to study the interfacial reactions between the fiber and matrix, oftentimes one uses very high temperatures in order to reduce the time necessary for the experiment. What are the objections to such accelerated tests?

• 4.3. What are the objections to the use of short beam shear test to measure the interlaminar shear strength (ILSS)?

• 4.4. Diffusion along free surface is faster than in the bulk of a material. Similarly, diffusion along a grain boundary is faster than in the lattice. Taking these factors into account, write an expression for diffusion coefficients in order of descent for diffusion along lattice, dislocation, grain boundary, reinforcement/matrix interface, and surface. Explain the reason behind your answer.

• 4.5. Discuss the importance of moisture diffusion in fiber reinforced polymer matrix composites. Recall that moisture absorption in PMCs is largely due to the permeability of the polymer matrix. Suggest some possible effects of moisture absorption in fiber reinforced PMCs in terms of effects on different moduli (along the fiber and perpendicular to the fiber) and ILSS.