Novel High-resolution Interferometric Materials Testing Device for the Determination of the Viscoelastic Behaviour of High-tech Plastics

− The use of high-tech plastics in the field of mechanical engineering is increasing dramatically. The time-dependent change of strain ε(t) during constant load (viscoelasticity, creeping) is a fundamental property of plastics and exact knowledge of these properties is required for the design of plastic parts. A novel high-resolution materials testing device is presented in this paper. It offers reaction-free interferometric measurement of the viscoelastic behaviour of plastics at a constant bending load. The resolution of the deflection is 1 nm. Therefore, unlike the three point bending test described in the ISO 899-2:2003 standard [1], the device is suitable for the measurement of viscoelasticity ε(t) at very small strain values (εmax < 0,1 %) and after a very short loading time (t < 1 d). A detailed description of the device and the parameters is shown as well as measurements of the time-dependent strain ε(t) of a high-tech plastic. Very good reproducibility of the measurements was achieved, which makes the device very suitable for measuring viscoelastic behaviour.