The impact resistance of composite materials — a review

High strength, high fracture toughness fibre composites with interface control—A review

The interfacial properties between carbon fibers and surrounding matrix of a composite are drastically affected by interfacial structure. This structure mainly relates to the surface physico-chemistry of the fiber, which includes its surface chemical groups and microstructure, morphology, surface area, and surface free energy. These properties can be changed by various surface treatments, including various dry and wet oxidation steps, plasma treatment, electrodischarge, and fiber sizing or coating. These methods improve the interfacial properties significantly and synergistically, although each treatment has its specific application area.

A review of methods for improving the interfacial adhesion between carbon fiber and polymer matrix

In this paper the various failure modes which occur in long fibre composites are described and discussed. The significance of each of these fracture mechanisms, in terms of their energy-dissipating capacity as well as their effect on the residual load-bearing properties, is considered. A brief review of both the destructive and non-destructive techniques used for detecting and characterizing defects and damage is presented. The ability of each technique to identify the various fracture mechanisms involved in the failure of long fibre reinforced composites is discussed and their overall suitability for damage detection evaluated.

The significance of damage and defects and their detection in composite materials: A review:

This article introduces the concept of an interphase in epoxy composites as being an identifiable entity which in some circumstances can control composite properties. The review is divided into two major parts. The first describes the interphase from a phenomenological viewpoint as to its possible structure and composition. Examples are given which serve to illustrate the potential for inducing compositional and structural differences at the reinforcement surface-epoxy interface. The second portion uses the results of micromechanical modeling of ideal composites to illustrate the magnitude and type of forces which operate in the interphase region. Specific examples are included which quantify the relationship between interphase structure and composite mechanical and fracture properties.

The interphase in epoxy composites

Fracturing of carbon fibre/polyester composites has been studied by means of mechanical testing and scanning electron microscopy. Carbon fibres were surface-treated in several ways so as to vary the interlaminar shear strength of the composites, and the effect of this variation on the work of fracture was determined by means of Charpy V-notch impact tests and slow three-point bend tests on notched specimens of triangular cross-section. The effect of moisture on the fracture toughness was also studied by measuring toughness and interlaminar shear strength after exposure to steam. Improvement of the fibre/resin bond results, as expected, in an increase in the brittleness of composites and it appears that a purely mechanical bond, such as might be obtained by acid-etching the fibre surface, is less proof against deterioration in humid atmospheres than a chemical bond, such as can be obtained by the use of coupling agents. Estimates of the magnitude of various contributions to the fracture toughness show that in carbon-fibre-reinforced resins the effect of increasing the stiffness or load-bearing ability of the matrix and the work done against friction in pulling broken fibres out of the matrix contribute approximately one fifth and four fifths, respectively, of the total work of fracture.

Strength and fracture toughness of carbon fibre polyester composites

Previous work has suggested that organosilanes applied to carbon fibres do not improve the interlaminar shear properties of reinforced plastics containing these fibres. However, by first oxidising the fibres in an aqueous environment, hydroxyl groups can be put onto the surface and the silanes are then able to form silanol bonds to the fibre surface as they do in glass fibre-reinforced plastics.

P. W. R. Beaumont

Papers

Strength and fracture toughness of carbon fibre polyester composites

Silane coupling in carbon fibre-reinforced polyester resin