Fracture toughness of composites

Tsai, H.C., Arocho, A.M. and Cause, L.W. (1990). Prediction of fiber-matrix interphase properties and their influence on interface stress, displacement and fracture toughness of composite materials. Mater. Sci. Eng. A126, 295-304. 

O Brien, T.K. and Martin, R.H. (1992). Results of ASTM round robin testing for mode I interlaminar fracture toughness of composite materials, NASA TM 104222. 

Cooper, G.A. (1970) The fracture toughness of composites reinforced with weakened fibers. J. Mater. Sci. 5, 645-654. 

Further details of the above techniques to improve the transverse fracture toughness of composites by controlled interfaces of various nature and modifying materials are discussed in the following sections. The effectiveness of these toughening methods on transverse fracture toughness and strength in relation to the controls are summarized in Table 7.1. 

Vf, fiber volume fraction neat resin fracture toughness mode 1 interlaminar fracture toughness of composite G),., mode II interlaminar fracture toughness of composite. 

The evaluations of short fiber reinforced composites for fracture behavior includes studies with respect to material parameters such as the fiber content [42,103,120], fiber length and orientation [69,97,103,115], and fiber bundling [115.120] testing conditions such as the temperature [24,42,121,122] and the loading rate [121,123,124] and fractography [42,43,103,123], The influence of some of these parameters, e.g fiber content, rate of loading, and the test temperature on the fracture toughness of composites can be presented in the form of property maps [125,126],... 

Schwartz HS, Hartness JT, Effect of fibre coatings on interlaminar fracture toughness of composites, Johnston NJ ed., ASTM STP 937, Philadelphia, ASTM, 150-178, 1987. 

Many matrix choices are available, and each type has an impact on the processing techniques, physical and mechanical properties, and enviromnental resistance of the finished part. Thermoplastic and thermoset materials can be resin matrices. Thermoplastic matrices have been developed to increase hot/wet use temperature and the fracture toughness of composites. Thermosetting resins, however, are more common. The common thermoset matrices for composites include polyester and vinyl esters, epoxy, bismaleimide, polyimide, and cyanate ester and phenolic triazine resins. 

These processes gradually decrease the strength and fracture toughness of composite elements. The rate of the processes is a function of environmental conditions humidity, temperature, and fibre and matrix properties that is, fibre sensitivity to corrosion and pH of the matrix. The main problem consists of identifying appropriate ways of prevention, which are ... 

Fracture toughness depends on matrix and fiber properties, fiber orientations, and stacking sequence. The emphasis on thermoplastic composites by the U.S. Air Force has been directed toward increasing the fracture toughness of composites. 

Figure 4.32 Typical methods of measuring fracture toughness of composites. (From Ref. 12)...

Table 17.2 Fracture toughness of composites, Gic, with different concentrations of nanosilica incorporated...

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