Próba dynamicznego rozciągania tworzyw sztucznych

The paper presents some results on dynamic tension tests of several polymers. A new device is applied and described. All impact experiments were performed with the aid of pendulum hammer type PSW-30 equipped with a special device designed at the Institute of Fundamental Technological Research of the Polish Academy of Sciences. The device, being the subject of patent, enables one to measure simultaneously the tensile force and displacement of the specimen grip as a function of time. Force and displacement is recorded independently on a two-beam oscilloscope and Polaroid camera. Having recorded the oscillogramme, the time can be eliminated and force-displacement curve obtained. However, the curve shows presence of some vibrations in the system of dynamometer-specimen-grips. Assuming a suitable vibration model it was possible to find out the parameters of the vibrating system and to calculate the real force acting on the specimen. If the analytical description coincides with the oscillogram – it means that the force was calculated correctly. Such procedure enables the indirect elimination of vibrations from the stress-strain curve. In the analytical description the method of ``connecting solutions'' was applied which makes possible to evaluate materials with a more complicated shape of its stress-strain curve (e.g. upper and lower yield point). Altogether three materials were tested: impact resistant polystyrene, PVC, and polypropylene. In all materials tested the critical strain rate was measured beyond which the fracturing of specimen without prior necking is observed. It means that in such a case the plastic flow is limited. As the result of experiments the diagrams have been obtained which demonstrate the effect of strain rate on the yielding stress, flow stress, and fracture stress for all materials tested.