Paper describes measurement of displacements and strains under environmental circumstances which have necessitated development of special techniques based on elementary optical interferometry. Examples are given of measurements at high temperature, high strain rate, and small deformations. Emphasis is on simplicity in the experimental set-up as well as in evaluation of tests. It is concluded that the methods described may be useful at times, as results can be obtained despite difficult circumstances although the resolution might be somewhat limited.

Previous uniaxial tests have shown that the viscoplastic behaviour of several polymers can be accurately described by means of the Rabotnov-Suvorova integral equation for materials with memory, for a wide range of loading rates in tension. Prediction of deformation can also be made in creep and relaxation. Present investigation concerns biaxial states of stress, achieved by simultaneously applying tensile force and torsional moment to thin-walled tubes. Results show that this constitutive equation, whose parameters were determined from uniaxial tensile tests at three different loading rates, also predicts the biaxial behaviour quite well until the torque comes close to the buckling load of the specimen. As a second verification, creep tests of a polyoximethylene membrane, subjected to hydrostatic pressure, were carried out. The validity of the equation is again confirmed.

Polymers are extensively used in engineering applications, ranging from sealing rings to dampers and springs in centrifugal separators as well as in micro robots with piezoelectric excitation. The mechanical behaviour of these materials is highly non-linear and may be described by integral equations, taking into account the load history of the part considered. Paper shows taht long-term deformation in creep and relaxation can be derived from tensile tests at several loading rates. The influence of cyclic loading is discussed. Tests show that material can fail in fatigue.

The criticality of rotor and stator contact in a large-size marine separator is studied by numerical modelling. Two plausible mechanisms leading to such contact, namely rolling of a ship in steady-state motion and a suddenly occurring unbalance in the rotor, are considered. It is found that contact due to sea motion may be tolerable, while sudden development of unbalance at operating speed can lead to unacceptably high contact forces. This agrees with experience of centrifugal separators operating on board of ships.

Polymers are extensively used in engineering applications, ranging from sealing rings to dampers and springs in centrifugal separators as well as in micro robots with piezoelectric excitation. The mechanical behaviour of these materials is highly non-linear and may be described by integral equations, taking into account the load history of the part considered. Paper shows taht long-term deformation in creep and relaxation can be derived from tensile tests at several loading rates. The influence of cyclic loading is discussed. Tests show that material can fail in fatigue.