High strain fibres

Polymers below the glass transition temperature are usually rather brittle unless modified by fibre reinforcement or by addition of rubbery additives. In some polymers where there is a small degree of crystallisation it appears that the crystallines act as knots and toughen up the mass of material, as in the case of the polycarbonates. Where, however, there are large spherulite structures this effect is more or less offset by high strains set up at the spherulite boundaries and as in the case of P4MP1 the product is rather brittle. 

The strength of a fibre is not only a function of the test length, but also of the testing time and the temperature. It is shown that the introduction of a fracture criterion, which states that the total shear deformation in a creep experiment is bounded to a maximum value, explains the well-known Coleman relation as well as the relation between creep fracture stress and creep fracture strain. Moreover, it explains why highly oriented fibres have a longer lifetime than less oriented fibres of the same polymer, assuming that all other parameters stay the same. 

Prewo, K.M., A complaint high failure strain, fibre reinforced glass matrix composite , J. Mat. Sci, 17, 3549-3563 (1982). 

Highly oriented fibres produce ESR signals imder tensile deformation in the ranges of 8 to 16% strain and 500 to 900 MN/m stress. They do not undergo yield and plastic flow for the simple reason that the molecules are already highly aligned in manufacture and their capacity for plastic flow has already been exhaused. Such fibres therefore represent one extreme of the various conditions in which polymeric solids are obtainable. 

The relative importance of these two (opposing) effects depends upon the material, the length and thickness of the specimen, and the test conditions, espiecially the strain rate. The drawing of fibres, film, and sheet in forming operations occurs at very high strain rates. 

Glass fibre composites have very good resistance to impact due to their high strain to failure, when compared with other fibres. 

FRC may be classified in conventional fibre-reinforced concrete (FRC) and high-performance fibre-reinforced concrete (HPFRC). They are composites that present a distinct stress-strain response in tension (Fig. 15.4). The... 

Naaman, A.E., 2003. Strain hardening and deflection hardening fibre reinforced cement composites. In Proceedings of the International RILEM Workshop - High Performance Fibre Reinforced Cement Composites - HPFRCC4, Ann Arbor, MI, pp. 95-113. 

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