Applied Mechanics and Materials Vol. 897

Abstract: . The influence of technological conditions on the strength characteristics of plasma-sprayed coatings of aluminum oxide powder with a fraction of 40–63 [μm], modified with a titanium oxide Nano powder with a particle size of 40–50 [nm], was studied. As independent variables (technological factors), which are the most significant and have the greatest influence on the strength characteristics of the coatings, there was chosen lens current, arc current, and the position of the solenoid relative to the nozzle. The adhesion strength and tensile strength of the coatings were adopted as optimization criteria. Mathematical models of the adhesion strength and the tensile strength of plasma coatings of aluminum oxide was obtained. As a result of multi-criteria optimization using the obtained mathematical models, the optimal combination of the levels of controlled factors was determined.

Abstract: Composite of Fe₃O₄/activated carbon was synthesized from activated carbon by mixing with Fe(II) and Fe(III) using ethanol and treated with hydrothermal process at 250°C for 2 hours. Previous treatment, activated carbon was prepared from palm oil shell using potassium hydroxide as a chemical activation and pyrolyzed at 500°C for 3 hours. Surface area composite of Fe₃O₄/activated carbon is 8.05 m²/g. However, the X-ray diffraction analysis shows that Fe₃O₄/activated carbon has crystalline phase which tend to amorphous phase. Characterization using FTIR show that the composite has Fe-O on 557 cm^-1. The Composite of Fe₃O₄/activated carbon has been successfully synthesized.

Abstract: In this paper, a frictionless contact of a rigid flat-ended indentor on a linear elastic half plane is investigated by taking the influence of surface and couple stresses into account. The surface elasticity and couple stress theories are utilized to form a mathematical model. The Green’s function method together with the equilibrium condition of the indentor is employed to formulate the key equations governing the contact pressure. A collocation technique and a set of available fundamental solutions of a half plane under the surface loading are adopted to determine the unknown contact pressure. Results from a numerical study reveal that the presence of both surface and couple stresses significantly alters the distribution of the contact pressure from that predicted by the classical linear elasticity, and the size-dependent characteristics of predicted solutions are obviously observed when the contact width is comparable to the internal length scales of the surface and bulk materials.

Abstract: This research aims to investigate the mechanical properties of engineered cementitious composites including compressive strength, splitting tensile strength, modulus of rupture, and load-deflection behavior. In addition, the abrasion test of concrete under water, which is recommended by ASTM C1138, was carried out and its results were compared with the splitting and modulus of rupture test results. Untreated low-cost polyvinyl fibers were used with different volume fractions of 0.5, 1.0, 1.5, and 2.0%. All tests were carried out at the standard age of 28 days. The experimental results showed that the use of 2% of low cost polyvinyl fibers with the engineered cementitious composites led to the increase of the splitting tensile strength and the modulus of rupture by 134% and 287%, respectively, compared to specimens incorporating no fibers. The results showed also that the deflection and the ultimate failure load increases as the fiber content increase.

Abstract: A novel nickel (Ni) and natural rubber loaded carbon nanofiber branches were prepared by electrospinning process followed by conventional heat treatment processes. This research utilized a one-step carbonization process using electrospun fibers from one-pot solution consisting of Ni, natural rubber cup lump (NR) and polyacrylonitrile (PAN). The as-spun nanofibers were successfully prepared for different types of NR-PAN and NiNR-PAN samples. The obtained nanofibers were stabilized at 260 °C for 2 h and then cooled to room temperature. The stabilized fibers were continued calcined at 900 °C for 1 h under N₂ atmosphere. Samples were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), and Field Emission Scanning Electron Microscopy (FESEM). NR-PAN sample showed a uniform surface whereas tiny branches were found on NiNR-PAN sample. The carbon nanofiber branches with 48.29 nm diameter were observed on the parent carbon fiber surface with 700-800 nm diameter. Furthermore, only metallic Ni nanoparticles was formed and the average size of Ni nanoparticles calculated XRD result was 14.15 nm. SEM images showed that Ni nanoparticles were well dispersed on CNFs.

Abstract: . A primary current focus in concrete shear design is how to ensure the shear resistance of the concrete structures to withstand the possible adverse creep effects during the service life. All shear-carrying actions are supposed to depreciate due to the enhanced critical shear cracks under sustained loads. However, only a few studies that evaluated the performance of concrete structures failing in shear due to long-term loading. As the longitudinal tensile reinforcement strain influences the shear strength of RC beam, the shear resistance of the beam under sustained load may also be affected by the amount of longitudinal reinforcement. The present study aims at investigating the influence of flexural reinforcement ratio on the shear creep failures of reinforced concrete (RC) beams without stirrups by non-linear finite element analysis. In this study, the numerical model of RC beams with reinforcement ratios varying from 0.4% to 3.2% was evaluated under different loading rates. A loading rate of 1000 and 10000 times slower than the static loading rate were adopted to reveal the creep effects of RC beams.

Abstract: Fly ash and ground granulated blast furnace slag (GGBFS) is a green construction material used to produce durable concrete. Experimental research on eco-concrete uses incorporating cement, fly ash and GGBFS. Fly ash and GGBFS replace different cement content by weighing, evaluating the workability, mechanical properties and durability of eco-concrete. The results also show that combining fly ash and GGBFS in concrete can create compressive strength concrete of 55MPa while the amount of cement used for 1m³ of co-concrete does not exceed 300 kilograms, the research also judges the water absorption, the chloride penetration resistance at 28 days with 30% replacement of GGBFS.

Abstract: Experimental studies of plasma surface treatment processes of various materials are difficult since temperatures of the surface are more than 1500-3000 K, the speed of their change is high (10⁴ K/s), the front of melting is moving. Theoretical researches of the thermal modes are necessary for conducting plasma processes in the best possible way. The use of analytical decisions at impulse thermal influence on the surface allows to calculate temperatures on the surfaces and in the mass of the material under almost any boundary conditions. The paper presents the results of calculation of various plasma processing at dielectric and steel materials (hardening, welding), as well as comparison of the obtained design parameters with experimental values.

Abstract: The paper deals with experimental analysis, which is focused on the use of acoustic measurement during the solidification process. As a material for monitoring was chosen fine-grained cementitious composites in the laboratory environment. For this purpose, a measuring device working on the principle of mechanical waves passing through the material was designed, assembled and verified. The experiment was conducted on cement pastes prepared from CEM I 42.5 R Portland cement with two different water coefficients (w/c = 0.40 and w/c = 0.33). The differences in the wave propagation in cement pastes were investigated. Simultaneously with this experiment, the monitoring and the saving records of the internal temperature was conducted. The results show the time of „critical changes" in the internal structure of the material can be determined. These changes are probably related to the quality of the particle’s bonds in the inner material structure, which is reflected in the propagation of mechanical waves. Overall, it is shown these experiments could be used to expand the understanding of the various processes occurring during early hydration of cement, and the application of these results to field situations (in the future) could lead to the other development of, non-destructive (and nonintrusive) monitoring techniques.

Abstract: Present research work reports a study on new mechanical phenomenon of the porous Ti-3.5Nb-3.5Zr materials that address for implant materials in dental. The mechanical testing samples were prepared by two-step sintering method with dimension of 10 mm and height of 10mm. The compressive tests were carried on MTS instrument to determine the strain-stress curves. Then mechanical behavior of the materials was analyzed from those curves. For samples after sintering without space holder and binder addition, there were three deformation regions on the curves that were linear elasticity, plateau and densification. The mechanical behavior of materials was modeled, and the main parameters in the model were identified from the strain - stress curve. For sample after sintering with space holder and binder, materials were brittle. The mechanical properties of those samples were also determined. Microstructures of materials before mechanical testing were observed by SEM, and the surface was also analyzed by XRD.