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Pultruded glass fibre reinforced plastics (or GRP) rod is being increasingly used in the area of cable design, used for strength members in optical fibre cables. The possibility of failure by the process of stress corrosion has resulted in the need to determine the reliability of the dielectric cables when in service. The viability of life predictions being made from the study of stress corrosion fracture surfaces is investigated. The production of static fatigue data for composite materials is needed to enable any accurate predictions to be made.

Isothermal crystallization of poly(tetramethylene ether glycol) (PTMEG) with relatively low molecular weight (Mn= 991, 2004 and 2864, respectively) was investigated by differential scanning calorimetry, and the equilibrium melting temperature (Tm0) determined using the Hoffman–Weeks analysis. The crystallization kinetics of PTMEG were characterized using an Avrami analysis. Mechanistic nvalues ranged from 2.2 to 2.9 for the primary crystallization process for three molecular weight grades, indicating heterogeneous nucleation of spherulites. Polarized light microscopy confirmed that PTMEG crystallized by the growth of spherulites from heterogeneous nuclei. The half–life for crystallization (t1/2) and the composite rate constant were found to be dependent on the degree of supercooling (ΔT) and the molecular weight. Copyright © 2006 John Wiley & Sons, Ltd.

Copolyesters were synthesized by using ring-opening polymerization of cyclic poly(butylene terephthalate) oligomers (c-PBT) and ε-caprolactone monomer (CL) in the presence of stannoxane catalyst at an elevated temperature. The in-situ copolymerization was conducted with various c-PBT/CL feed ratios. The copolyesters were characterized by GPC, NMR, and FT-IR techniques. Phase separation and the relaxation behavior of the resultant copolyesters were investigated by DSC, DMTA, and dielectric spectroscopy measurements. Mechanical properties (stress−strain behavior) are also reported and can be adjusted by varying the ε-caprolactone content of the copolymer.

An analysis of the mechanics of the die-drawing process for polymer orientation has been undertaken on the basis of the lower bound theory by Hoffman and Sachs for metals, with several important modifications. First it is accepted that the flow stress in polymers is strongly dependent on plastic strain, strain rate and temperature. Secondly, thermal effects during die drawing due to heat generated by plastic deformation are included in the analysis. Finally, the temperature distribution in the die is estimated, taking into account both heat condition and axial translation of the polymer during the drawing process. Good agreement was obtained between theoretically predicted drawing stresses and those determined experimentally for a range of drawing speeds.

A design of a four square gear test rig that allows the wear of polymer and composite gears to be monitored continuously during operation is described. The wear behavior of three typical gear materials is examined and it is shown that the wear characteristics differ greatly. For Acetal there is a sharp rise in wear as the transmitted torque is increased, effectively limiting the torque that can be transmitted by an Acetal gear pair. This wear transition is shown to be associated with the maximum surface temperature of the gear reaching the melting point of Acetal. This provides an indirect method of checking the accuracy of existing models for the maximum surface temperatures in polymer gears. Very large discrepancies are found. A simple, alternative model for the average and maximum gear temperatrues is developed and is shown to predict the wear transition with far greater accuracy.

A design of a four square gear test rig that allows the wear of polymer and composite gears to be monitored continuously during operation is described. The wear behavior of three typical gear materials is examined and it is shown that the wear characteristics differ greatly. For Acetal there is a sharp rise in wear as the transmitted torque is increased, effectively limiting the torque that can be transmitted by an Acetal gear pair. This wear transition is shown to be associated with the maximum surface temperature of the gear reaching the melting point of Acetal. This provides an indirect method of checking the accuracy of existing models for the maximum surface temperatures in polymer gears. Very large discrepancies are found. A simple, alternative model for the average and maximum gear temperatrues is developed and is shown to predict the wear transition with far greater accuracy.

The wear and friction behaviour of short glass-fibre-reinforced polyamide 66 composites running against each other, unlubricated, in non-conformal, rolling-sliding contact has been investigated. Both a wide range of loads and slip ratios and a range of samples with different fibre concentration and different crystallinity have been examined. Short glass-fibre reinforcement makes the polyamide 66 exhibit unique tribological behaviour. There is a high resistance to wear and friction which results from a significant “self-lubricating” property. A thin film layer exists on the contacting surfaces when two discs run against each other within the range of the test conditions. It is this thin film that plays a dominant role in the “self-lubricating” property of the composite. The formation of the thin film and the life of the composite depend on a complex of interactions between structure, strength and fibre concentration, and the specific conditions of load and slip ratio imposed. Under identical loading conditions, either lower fibre concentration or lower crystallinity cause the thin film to form continuously during the wear process so that the life of the composite may reach 6×106-107 cycles. It is suggested that the “self-lubricating” property may be used in the working period of engineering components rather than only during the temporary running-in period of machine elements.