Evaluation of Mechanical Properties of a Polymeric Material Used in the Construction of Boxes for Electrical Energy Measurements

The mechanical properties of polymeric materials depend strongly on the processing. In this work, blends of Poly(phenylene oxide)/polystyrene (PPO/PS) and polycarbonates used in electrical cabinet boxes have been studied. A comparison was made of the mechanical properties of samples injected in the form of test specimens, according, to the standard practice ASTM D638, with test specimens removed from the boxes. From the results of impact Izod test, a great variability in the values was verified before and after ageing in water. for all the boxes. This is due to the different internal tensions in each region of the box arising from the processing. A large difference was observed among the values found for resistance to the impact Izod test of the removed test specimens of the lower part of the boxes compared with the values found for the respective injected materials. This indicates a significant influence from the parameters of injection processing, in the boxes as well as in the injected test specimens. Overall, the values of tensile strength in the point of maximum elastic deformation do not differ significantly among the test specimens injected and the removed from the boxes of the same material; however, it was observed that this variation is significant in the values of elongation at break, demonstrating that this property must be considered in the evaluations of the mechanical behavior of the polymeric materials.