Time and temperature effects on Poisson’s ratio of poly(butylene terephthalate)

Abstract

The viscoelastic nature of the Poisson's ratio of a semicrystalline poly (butylene terephthalate) is highlighted by investigating its dependence on time, temperature and strain rate, under two types of loading conditions: i) constant defor- mation rate tests, in which the transverse strain is measured in tensile ramps at various temperatures and at two strain rates; and ii) constant deformation tests, in which, under a constant axial deformation, the transverse strain is measured as a func- tion of time in isothermal experiments performed at various temperatures. In both testing configurations, axial and trans- verse deformations are measured by means of a biaxial contact extensometer, and a correction procedure is adopted in order to compensate the lateral penetration of the extensometer knives. Poisson's ratio displays the typical features of a retarda- tion function, increasing with time and temperature, and decreasing with strain rate. This behaviour has been compared to that of simultaneously measured relaxation modulus.