Design & Testing # 1998 Gothenburg
One of the characteristic behaviours of plastics (or viscoelastics) materials is the creep phenomenon, which is defined as the continuing deformation under a constant load with time. Although research on creep of plastics pipes has been widely carried out in other plastics, little work has been reported for creep in ABS (acrylonitrile-butadiene-styrene) pipes at high temperatures. In this paper, the generalised Kelvin series of formulae, which consists of six Kelvin elements, a power model, as well as linear regressions, are applied to the experimental data measured from creep tests under constant bending stresses at different temperatures. The least-squares method was used to adjust Kelvin model parameters, and a LevenbergMarquardt non-linear least-squares regression procedure was used to determine the creep parameters in the power model. This led to an empirical formulae of creep compliance equal to the reciprocal of the creep modulus. This creep modulus can provide a means to evaluate the long-term structural properties for different resins used in pipe production.