The present work has the objective of studying the effect of shot peening with glass microspheres on SAE 1020 steel in its resistance to fatigue. Fatigue tests were carried out by rotary bending with load control and loading on balance in specimens with and without shot peening. A rotation speed of approximately 750 rpm (12.5 Hz) was employed in the fatigue tests. Vickers microhardness tests were performed in order to verify the surface hardening produced by shot peening with glass microspheres. Analysis of the steel surface and fatigue fractures was performed using scanning electron microscopy (SEM). Fatigue tests were performed in order to obtain S-N curves (Wöhler curves). It was observed that shot peening with glass microspheres improved the fatigue strength of the steel at high cycle.

The injection moulding conditions may change the degree of crystallinity of the plastic to some extent, which affects the mechanical properties such as tensile strength and hardness. Moreover, the cooling conditions of the moulded parts may contribute to changes in their shrinkage. The paper presents the results of determination of the melting enthalpy of a polypropylene. The melting enthalpy ∆ H_m was determined by differential scanning calorimetry. It was found, that the value of the melting enthalpy depends on the physical conditions prevailing during the sample production process, such as the temperature of the liquid material, the cooling rate of the plastic (related to the mould temperature T_m) and the flow rate of the plastic in the mould. The degree of crystallinity of the obtained samples was also determined, which, depending on the measured enthalpy of fusion, influences the degree of structural order of the polymer. Standardized test samples were also analysed in terms of transversal shrinkage and longitudinal shrinkage. The shrinkage of the injection moulded parts results from the change of physical state of plastic during its solidification in the mould.