Tom 22 (2022): Zeszyt 4 (December 2022)

The fatigue process under fretting conditions is characterized by small oscillatory movements due to vibrating or cyclic loads between two surfaces in contact. Two phenomena can arise as a consequence: the surface wear of the bodies in contact, giving rise to the so-called fretting wear. The second phenomenon concerns crack nucleation in the contact region, causing a reduction in the fatigue strength of the component subjected to cyclic loading. This process is called “fretting fatigue”. In the present study, finite element models (2D-FEM) are provided to demonstrate the effect of pad radius on the contact parameters such as: contact pressure, shear traction, stresses, sliding, size of contact line and crack nucleation and its location along the contact line of aeronautical Al2024 alloy under fretting fatigue loading. Six numerical models are utilized to describe the effect of changing pad radii on contact stresses and damage of crack nucleation. The Ruiz parameter criterion should be used to predict the location of crack initiation in the contact zone. Comparison of the finite element results shows that there is a good agreement between the numerical modeling predictions with those analytical results. The stress field, relative slip, and damage parameters in fretting fatigue loading were highlighted. The pad radius substantially affects the distribution of contact parameters. Particular attention must be taken into consideration to this variable when analyzing the structure in fretting fatigue.

Core sampling is the most accurate method of evaluating the compressive strength of concrete structures. However, it is preferable to take only small cores to avoid damaging the structures. It turns out that various elements influence the strength of compressed cores. This study examines the influence of specimen size, aggregate size, concrete class, and curing method on compressive strength. Three aggregates measuring 3/8, 8/15, and 15/25 mm are used to make six sets of concrete compositions with strengths of 25 MPa and 30 MPa. Nine specimens are made, one for each variety of aggregate and concrete. Cores of 100 mm, 75 mm, and 50 mm sizes are made. These cores are extracted from concrete blocks curing in the outside air to simulate the real concrete curing environment. Cast specimens cured in water and air with diameters of 50 mm, 100 mm, and 150 mm are also made. The objective is to compare the average compressive strength of all cast or extracted specimens with that of cylindrical standard specimens of diameter 150/300 mm and the cores and cast specimens. The obtained findings showed that the compressive strength is overestimated when we compare f_p100 cores and standard air-cured specimens (f_c), with a conversion factor varying from 0.69 to 0.96. However, a decrease is observed in comparison with water-cured specimens. The use of f_p75 cores reduced the conversion factors, which are between 0.83 and 0.87 for B25 concrete. The highest f_p/f_c ratios are obtained for f_c50 cores, which can reach 1.24. It turns out that the size of the core and the class of concrete have a much greater influence on the f_p/f_c ratios.

Welding is an indispensable manufacturing process in the shipbuilding industry. The fierce competition involved often necessitates a cost-effective and reliable welding method. In this study, the weldabilities, microstructures and some mechanical properties of ASTM A131 (Grade A) steel joints fabrication by submerged arc welding (SAW), metal active gas (MAG) welding and plasma arc welding (PAW) have been investigated. The microstructures of the welds were examined by optical microscopy. The mechanical properties of the joints were determined by microhardness measurements, tensile and impact tests. The results showed that tensile strength of the joints reached a tensile strength of up to 462 MPa. The locations of the fractures were always adjacent to the base metal. The Charpy impact energy of the weld metal reached a value of 72.5 J, which was 25 % higher than that of the base metal at 57.7 J. A relatively high hardness of 221 HV was obtained in the PAW method compared to 179 HV in the base metal.

Polyethylene terephthalate is a synthetic material known as PET. PET strapping bands is a material commonly used in all industries for packaging and bundling. The excessive use of this material has led to the pollution of the urban environment, which necessitated the search for effective solutions to dispose of this waste. The treatment and reuse of these materials is among the best solutions that contribute to reducing environmental pollution on the one hand and enabling the obtaining of economical products on the other hand.

The main purpose of this experimental study is to valorize dune sand mortar and PET waste in the manufacture of cement mortar. It also aims to investigate the impact of the inclusion of recycled PET fibers on the physical and mechanical properties of the reinforced mortar. The study was carried out in several phases; after a physical and chemical characterization of the materials used, a method for the composition of mixtures was proposed, which is based on the progressive substitution of dune sand by recycled PET fibers. The quantity of cement added to each mixture is fixed at 450 g, and that of dune sand and fibers is taken as equal to 1350 g. In order to properly examine the influence of the incorporation of fibers on the properties of the reinforced mortar, the substitution rate of dune sand by the fibers varied from 0% to 2.5% with a step of 0.5%. For each mixture, many characteristics of the mortar were tested, such as consistency, bulk density, compressive strength, and flexural strength. The results obtained show that the incorporation of PET fibers has a significant effect on the fresh and hardened properties of the treated mortar.

The fundamental aim of the research is to investigate the microstructure and mechanical properties of the AA2519-T62 laser beam welded joints obtained with various values of welding velocity. For the constant value of laser power (3.2 kW) three joints have been produced with various values of welding velocity: 0.8, 1.1, and 1.4 m/min. The joints have been subjected to microstructure analysis (including both light and scanning electron microscope), microhardness measurements, tensile tests, and fractography of tensile samples. The established values of joint efficiency contain within the range of 55-66% with the highest value (66%) reported for the joint obtained with 1.1 m/min welding velocity. The produced welds have noticeable participation of pores, which tends to increase together with the value of welding velocity. In all cases, the failure has occurred in the fusion zone by ductile fracture.

In the present study, a modified duplex melting process was set up so as to be able to produce an EN-GJL-150 gray cast iron from a local manganese-rich pig iron. A descriptive statistics showed an average Mn and Si content in raw material such that: Mn % = 2.457±0.133 and Si % = 0.682±0.088. The demanganization process was run and monitored in a cascade of two industrial-scale furnaces: a rotary kiln and an electric arc furnace. The performed experiments indicated that: 1) the manganese content decreased from 2.45 % to 0.94 %, 2) the manganese oxidation obeys the first order kinetic model, 3) Brinell and Rockwell hardness’s decreased by 38.83% and 27.81% respectively, and 4) the produced cast iron has a pearlitic microstructure with a small fraction of ferrite (1 to 5%) in the matrix and traces of cementite. All results showed that the produced castings comply with the standards in force for EN-GJL-150 cast irons, similar to gray cast iron ASTM A48 Class 20.

The literature is flooded with scientific information on most durability properties except water absorption coefficient of masonry units like sandcrete blocks. Also, while waste papers disposal is a systemic problem due to ineffectiveness of waste management system in developing countries, the price of cement is on the increase. This situation, ultimately, causes a bane in achievement of low-cost housing development considering the fact that sandcrete blocks are predominantly used as walling elements for such undertakings. In this study, solid core sandcrete blocks were produced with waste paper ash (WPA) utilized as partial replacement of cement at 5 % and 10 % volumetric levels. Chemically, the WPA was found to show similarity with cement in terms of SiO₂, Al₂O₃, and CaO contents. Density and water absorption coefficient of the block samples were determined. While density ranged from 1682 to 1872 kg/m³, water absorption coefficient varied from 27.04 to 23.49 kg/m²h^0.5. Statistically, no significant difference was revealed at p < 0.05 between experimentally-measured water absorption coefficients and those obtained using the model developed for prediction based on density of the samples. Thus, utilization of WPA as described herein could help to reduce the cost of procuring cement and in turn, enhance low-cost building construction. Also, with the developed model (showing dependence of water absorption coefficient on density), durability of sandcrete blocks exposed to moisture –prone environment could be easily predicted.

The stability of nonlinear nanofluid convection is examined using the complex matrix differential operator theory. With the help of finite amplitude analysis, nonlinear convection in a porous medium is investigated that has been saturated with nanofluid and subjected to thermal modulation. The complex Ginzburg-Landau equation (CGLE) is used to determine the finite amplitude convection in order to evaluate heat and mass transfer. The small amplitude of convection is considered to determine heat and mass transfer through the porous medium. Thermal modulation of the system is predicted to change sinusoidally over time, as shown at the boundary. Three distinct modulations IPM, OPM, and LBMOhave been investigated and found that OPM and LBMO cases are used to regulate heat and mass transfer. Further, it is found that modulation frequency (ω_f varying from 2 to 70) reduces heat and mass transfer while modulation amplitude (δ₁varying from 0.1 to 0.5 ) enhances both.