Tough matrix material

Impact strength is increased significantly for brittle materials (PLA) and materials with low notched impact strength (e.g., PP) in particular at reduced temperatures when a matrix glass transition is passed (e.g., PP). Impact strength of very tough matrix materials cannot be improved however, values remain on a high level. 

Ceramic matrices are usually chosen on their merits as high temperature materials reinforcements are added to improve their toughness, reUabiUty, and damage tolerance. The matrix imparts protection to the reinforcements from chemical reaction with the high temperature environment. The principal concerns in choosing a matrix material are its high temperature properties, such as strength, oxidation resistance, and microstmctural stabiUty, and chemical compatibihty with the reinforcement. 

The word "composites" has a modern ring. But using the high strength of fibres to stiffen and strengthen a cheap matrix material is probably older than the wheel. The Processional Way in ancient Babylon, one of the lesser wonders of the ancient world, was made of bitumen reinforced with plaited straw. Straw and horse hair have been used to reinforce mud bricks (improving their fracture toughness) for at least 5000 years. Paper is a composite so is concrete both were known to the Romans. And almost all natural materials which must bear load - wood, bone, muscle - are composites. 

The mechanical properties of the blend of silane/size and bulk epoxy matrix (at concentrations representing likely compositions found at the fiber-matrix interface region) also suggest that the interaction of size with epoxy produces an interphase which is completely different to the bulk matrix material (Al-Moussawi et al., 1993). The interphase material tends to have a lower glass transition temperature, Tg, higher modulus and tensile strength and lower fracture toughness than the bulk matrix. Fig. 5.4 (Drown et al., 1991) presents a plot of Tg versus the amount of... 

The descriptions presented in the foregoing sections are concerned mainly with composites containing brittle fibers and brittle matrices. If the composite contains ductile fibers or matrix material, the work of plastic deformation of the composite constituents must also be taken into account in the total fracture toughness equation. If a composite contains a brittle matrix reinforced with ductile libers, such as steel wire-cement matrix systems, the fracture toughness of the composite is derived significantly from the work done in plastically shearing the fiber as it is extracted from the cracked matrix. The work done due to the plastic flow of fiber over a distance on either side of the matrix fracture plane, which is of the order of the fiber diameter d, is given by (Tetelman, 1969)... 

Agarwal, B.D. and Glare, G..S. (1982). Influence of the properties of the matrix material on the fracture toughness of short fiber composites. Mater. Sci. Eng. S2, 139-145. 

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