Composites are materials formed by two dissimilar materials. For most practical applications, the materials consist of fibers and a matrix. The fibers, such as carbon fibers or fiberglass, are generally long, flexible, and strong. The matrix, usually a polymer based substance, provides the rigidity that hold the fibers in a shape and withstand compressive forces. These materials are combined to produce a material that is both rigid and strong. For ICME analysis, the composite material most be analyzed as two separate materials then combined using the fiber-matrix bridge. Each material can be analyzed through ICME methodology to determine the properties of the base materials, then additional analyses are performed on the fiber matrix bridge to determine the strength of the bond. This information, along with the desired volume fractions for each of the materials can be used to determine the properties of the composite material.
The bond between the fibers and the matrix and the volume fraction of each are the keys to determining the properties of the combined material. This bridge is different for each material. Most fiber based composites contain fibers that are coated with chemicals called sizings that either protect the fiber or promote bonding. For example, glass fibers are coated sizings that promote chemical bonding to matrix materials, while carbon fibers are coated with sizings that protect the fibers from each other prior to their use. The carbon fiber sizings can inhibit chemical bonding between the matrix and the fibers. In this case, other methods of preventing slip between the fiber and the matrix are needed. To prevent slip, carbon fibers are etched prior to application of the sizing to promote a frictional bond between the fibers and the matrix.
An understanding of the specific sizing and its role leads to a better understanding of the composite material. To properly analyze the bond, one needs to determine the length scale of the fiber-matrix bridge(s). For example, a chemical bond might require an atomistic analysis, but an etched bond might require a mesoscale analysis.
- ↑ Strong, B. “Practical Aspects of Carbon Fiber Surface Treatment and Sizing.”