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The fracture of filled epoxy resins

Lilley, J

The fracture of filled epoxy resins Thumbnail


J Lilley


The useful structural materials are those that are both strong and tough. The "toughness" of a given material is characterised by its fracture energy which is refined as the total work expended in propagating the crack so as to produce unit area of new fracture surface: the fracture energy is a characteristic property of the material and may be determined by direct experiment.
Earlier work had shown that the addition of particulate fillers to a "brittle" epoxy resin matrix produced composite materials having fracture energies somewhat greater than that of the base matrix. The main object of this work was to examine in detail the fracture characteristics of the above family of materials with a view to identifying the physical mechanisms responsible for this effect. Hence, a reasonably systematic examination of the effect on toughness of the size, shape, nature, concentration and adhesion of the matrix to the filler particles has been undertaken.
Estimates of the fracture energies of three epoxy resin systems, i.e. CT200/H1901, L Y558/H1973 and EPON828/NMA/BDMA and related composites have been made by a double cantilever beam technique. Chapter I contains a detailed review of the mechanics of such a system: the basic experimental techniques and the specimen preparation procedures are described in Chapter II. It was considered that before any detailed conclusions could be drawn about the crack propagation processes in the composites, more detailed information than was at present available was required on the base matrices. These experiments are described in Chapter III and the results indicate that our cured epoxy resins exhibit a "jumping"mode of crack propagation and are therefore characterised by two fracture energies which correspond to conditions of crack initiation and arrest. The effect of fillers on the fracture toughness of our epoxy resins is described in Chapter IV: these results are compared with the Charpy
Impact Energies in Chapter V.
The possibility of interpreting the crack propagation behaviour in the base matrices in relation to variations in crack opening displacements and flow stresses seemed attractive and hence these parameters were determined and are presented in Chapter VI. Finally in Chapter VII the "jumping"mode of crack propagation is discussed in detail, and a simple mathematical model is developed which predicts correctly the type of changes in fracture energy that may be expected when particulate fillers are added to an epoxy resin matrix.


Lilley, J. (1973). The fracture of filled epoxy resins


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