Tom 17 (2017): Zeszyt 1 (March 2017)

The presence of the oxide layers on Zr alloys may retard or enhance the hydrogen entry and material degradation, depending on the layer features. This research has been aimed to determine the effects of pre-oxidation of the Zircaloy-2 alloy at a different temperature on hydrogen degradation. The specimens were oxidised in laboratory air at 350°C, 700°C, and 900°C. After, some samples were tensed at 10-5 strain rate and simultaneously charged with hydrogen under constant direct voltage in 1 N sulfuric acid at room temperature. Other specimens were charged without any tension, then annealed at 400°C for 4 h and finally tensed at above strain rate. The SEM examinations were performed on the cross-sections and fracture faces of specimens. The obtained results demonstrate the effects of the oxide layer on the cathodic current and hydrogen entry, mechanical properties and the appearance of hydrides and fracture behaviour.

In hydrocarbon and maritime industry there is a constant need of materials and coatings withstanding severe conditions. One of adverse phenomena present there is cavitation erosion. The paper presents evaluation of cavitation resistance of three different steel coatings. Belzona 2141 (ACR-Fluid Elastormer), 1321 (Ceramic S-Steal) and 5831 (ST-Barrier) were deployed on P110 steel and subjected to ultrasound cavitation in distilled water and drilling mud environment. According to mass loss measurements Belzona 2141 shows superior performance comparing to two other coatings and bare p110 steel surface. This is due to its high elasticity comparing to steel.

Medium-carbon alloy steels containing different aluminum contents were hot forged by 95% reduction at 1200°C followed by air cooling. Optical and scanning electron microscopes were used to investigate the morphologies of the different phases present. An austentizing process followed by water quenching (after hot forging) was carried out to obtain different hardness values. The intensity of the different planes was investigated using X-ray diffraction. The mechanical properties were characterized using tensile and hardness tests. Optical and scanning electron micrographs revealed a great effect of aluminum content on the steel properties. A matrix of bainite and pearlite and traces of ferrite was revealed for hot forged steel type 1 containing 1% Al. Steel type 2 containing 2% Al showed a matrix of pearlite and ferrite with the absence of bainite. The hardness increased with increasing the temperature to a maximum value then decreased for steel containing 1 and 2% aluminum. After austentizing at 925°C, the maximum hardness of 649Hv was recorded for hot forged steel type 2 of 2% aluminum, while steel type 1 of 1% aluminum showed a maximum hardness of 531Hv after austentizing at 1000°C. Thus, the maximum hardness of hot forged steels decreased with increasing aluminum content. In addition, the maximum tensile and yield strength were decreased by increasing the aluminum content in the steel. The changes in microstructure and mechanical properties of these steels could be explained by the effect of aluminum as a ferrite forming element.

There is a continuous demand for high performance composite propellant formulations to meet mission requirements. The performance of composite propellant formulations can be enhanced by optimizing propellant formulation. However, the main objective of this study is to formulate a composition for composite propellant by optimizing the specific impulse which is the measure of propellant performance. A central composite design (ccd) consisting five ingredients (ammonium nitrate, powdered aluminum, polyester resin, ammonium dichromate and powdered charcoal) at five levels was used to formulate optimum propellant formulation from composite materials of ammonium nitrate based propellant verified for propellant characteristics using propellant performance evaluation programme (propep 3). The responses evaluated are specific impulse, characteristic velocity, density, temperature and molecular weight. Response surface methodology was used to analyze the results of the ccd of the composite formulations. The optimum values for specific impulse, characteristic velocity, density, temperature and molecular weight of the mixture from the surface plot are 212.178 s, 1335.81 m/s, 1640.6 k g/m3, 1968.73 k and 21.7722 g/mol respectively. The optimum predicted specific impulse was 212.178 s at composite composition of 73.61% ammonium nitrate, 4.36% powdered aluminum, 14.39% polyester resin, 5.10% ammonium dichromate and 2.54% powdered charcoal. The propellant optimum composition validated with propep 3 are in good agreement with each other in their accompany propellant characteristics. Therefore, the optimal propellant formulation enhanced the performance of solid propellants.

This paper deals with results of preliminary analysis to determine the bending strength of approximately 150 year old oak timber obtained from structural elements used in construction. The test procedures were those specified in the PN-EN 408 standard. The experiments involved subjecting specimens to four-point static loading using three different loading rates: 5, 7 and 10 mm/min. The specimens were sampled from full-size timber beams. The experimental data revealed that after such a long period of use the structural oak timber elements had retained high strength. The failure mode and the behaviour of the beams during tests were dependent on the location of wood defects as well as the rate of deflection gain in time.

In this paper the results of mechanical studies of the Aropol 536 composite on the epoxy-resin base are described. The aim of the studies was to measure elastic-plastic changes in the composite during its deformation. The obtained results were analyzed using Kolmogorov-Sinai metric entropy. The entropy was computed applying phase portraits reconstructed from a phase plane using delayed coordinates. Resolution of the particular experimental setup limits the number of the acquired data points, i.e., from several to tens of thousands of points and it has significant influence on accuracy of the obtained results. In conclusion, in the tested composites elastic-plastic deformations are periodic and repeat in a distinctive way in a wide range of deformations of the sample. Deformation of the elastic-plastic composite are associated with its complex structure and studies of its mechanical properties require more advanced methods such as use of Kolmogorov-Sinai metric entropy.