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Coarse Aggregate Size Effect on Non-linear and Uncertainty Mechanical Behaviors for Concrete
Issue:
Volume 8, Issue 3, September 2019
Pages:
100-107
Received:
9 April 2019
Accepted:
Published:
19 July 2019
Abstract: A series of uniaxial compression tests and simulations were conducted to evaluate the influences of single coarse aggregate (CA) size on the mechanical properties of concrete and their uncertainties. In this research, the specimens of pure mortar matrix and specimens with diameter 15 mm and 30 mm of single spherical steel aggregate were fabricated and tested by a material testing system. Based on experimental results, the mechanical parameters, including the elastic modulus, compressive strength, strain at the peak stress and absorbed strain energy were investigated. It was found that larger size of CA results in higher elastic modulus and compressive strength. Meanwhile, the strain at peak stress and absorbed strain energy of concrete are non-linear with the size of CA. And then, the mechanical properties were analyzed in the aspect of ITZ which is closely related to the size of CA. In addition, simulation results were presented to discuss the stress distribution of different size CA in specimen. In conclusion, the CA size has significant effect on the uncertainty of elastic modulus, strain at the peak stress and absorbed strain energy, but has little effect on the compressive strength. The findings from the current study will help gain the insights into the non-linear and uncertain mechanical behaviors of concrete.
Abstract: A series of uniaxial compression tests and simulations were conducted to evaluate the influences of single coarse aggregate (CA) size on the mechanical properties of concrete and their uncertainties. In this research, the specimens of pure mortar matrix and specimens with diameter 15 mm and 30 mm of single spherical steel aggregate were fabricated ...
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Simulation and Experimental Test in Tensile Behaviour of Austenitic Stainless Steels
Pham Quang,
Trinh Huu Toan
Issue:
Volume 8, Issue 3, September 2019
Pages:
108-111
Received:
5 June 2019
Accepted:
18 July 2019
Published:
31 July 2019
Abstract: In the systems of fuel cell (FC) and nuclear safety (NS) components many liners of ultra-high pressure tanks and pipes are directly exposed to hydrogen. Austenitic stainless steels are used as material for FC and NS components because of their high resistance to hydrogen intrusion. It is reported that hydrogen degrades mechanical properties of metals significantly. In the hydrogen-charged specimen of SUS 304, a desired model would be able to capture the mechanisms found in experimental testing like large strain elasticity, rate dependence, amplitude dependence, creep and damage. Thus, a prediction of material failure/fracture, including its behavior at large plastic deformations is of importance. To validate existing failure models, the finite element (FE) simulations are used in terms of dependence on length scale and strain state. Restrictions made the selection limited to, in Abaqus, already existing models. Axisymmetric simulations are performed in Abaqus to verify the material model required in order to capture the necking phenomenon in tensile testing. The elasto-plastic modeling in the FE simulations is directed ultimately to initiation and propagation of tension processes. Furthermore, numerical simulation results using the sub-models of crack-tip meshes are discussed. In our experiments, the tensile test system MTS at a crosshead speed of 1 mm/s are conducted, which enabled accurate monitoring of displacements on the specimen surfaces. When a material reached the limit of its capacity to carry further loading, deformations localize into necking and became highly dependent on the length over which the strain evaluation is performed the length scale.
Abstract: In the systems of fuel cell (FC) and nuclear safety (NS) components many liners of ultra-high pressure tanks and pipes are directly exposed to hydrogen. Austenitic stainless steels are used as material for FC and NS components because of their high resistance to hydrogen intrusion. It is reported that hydrogen degrades mechanical properties of meta...
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Nickel Oxide Nanocrystalline Fabricated Under Gamma Irradiation and Its Photocatalytic Investigation for Textile Azo Dye Degradation
Ekoko Bakambo Gracien,
Muswema Lunguya Jérémie,
Lobo Kanza-Kanza Joseph,
Mvele Muamba Omer,
Nzazi Kambamba Nicole,
Nduku Mafwa Fabrice,
Musengele Bilasi Denis,
Ndonganzadi Tresor,
Mukiatom Perbon,
Mata Niasa Gérard
Issue:
Volume 8, Issue 3, September 2019
Pages:
112-119
Received:
4 July 2019
Accepted:
25 July 2019
Published:
13 August 2019
Abstract: Gamma irradiation technique has been applied to produce non-stoichiometric nickel oxide nanoparticles (of approximately 23 nm) from gels prepared at pH about 8.2. Characterization techniques so far discussed in this investigation revealed that the sol product prepared before irradiation corresponded to Ni(OH)2, which was transformed under gamma irradiation to NiO. The present investigation has proven the efficiency of gamma rays in inducing changes in structure and morphology of the sols prepared before irradiation. The synthesised NiO nanoparticle was found to be an efficient photocatalyst for degradation of acid red G under UV light irradiation. And, finally the radiolytic mechanism production of NiO nanoparticles in aerated solutions is suggested according to the experimental result.
Abstract: Gamma irradiation technique has been applied to produce non-stoichiometric nickel oxide nanoparticles (of approximately 23 nm) from gels prepared at pH about 8.2. Characterization techniques so far discussed in this investigation revealed that the sol product prepared before irradiation corresponded to Ni(OH)2, which was transformed under gamma irr...
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Hot Corrosion Behaviors of CoCrFeNiTi0.5 High Entropy Alloy in the Mixture Salt of Na2SO4-25%K2SO4 and Na2SO4-25%NaCl at 750°C
Li Ping,
Zhao Jie,
Li Tingju,
Pang Shengjiao
Issue:
Volume 8, Issue 3, September 2019
Pages:
120-126
Received:
7 August 2019
Accepted:
28 August 2019
Published:
10 September 2019
Abstract: Hot corrosion behaviors of CoCrFeNiTi0.5 high entropy alloy pre-coated various mixture salt in air at 750°C were investigated respectively by using weight change kinetics, X-ray analyses, SEM equipped with EDS and EPMA. The results indicate that CoCrFeNiT0.5 alloy exhibits relatively high corrosion resistance in Na2SO4-25%K2SO4 molten salts. The cross-section is divided into three parts: the oxide scale composed of various oxides, the corrosion affected zones with some micro-pores as well as minor of sulfides and the matrix. The addition of NaCl to Na2SO4 destroys seriously the integrity and compactness of the oxide scale and induces the formation of more micro-pores as well as sulfides in the corrosion affected zone, which accelerates the propagation of hot corrosion. As a result, the alloy suffers from more severe corrosion in Na2SO4-25% NaCl than in Na2SO4-25%K2SO4. Hot corrosion of the alloy in Na2SO4-25%K2SO4 is explained based on the oxidation and the basic fluxing of Cr2O3 in molten Na2SO4. However, hot corrosion process in Na2SO4-25% NaCl is dominated by the interaction of oxidation and chlorination. In addition, the internal sulfidation of Fe and Ni also contributes to hot corrosion of the alloy in both Na2SO4-25%K2SO4 and Na2SO4-25% NaCl mixture salt.
Abstract: Hot corrosion behaviors of CoCrFeNiTi0.5 high entropy alloy pre-coated various mixture salt in air at 750°C were investigated respectively by using weight change kinetics, X-ray analyses, SEM equipped with EDS and EPMA. The results indicate that CoCrFeNiT0.5 alloy exhibits relatively high corrosion resistance in Na2SO4-25%K2SO4 molten salts. The cr...
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Study of the Mechanical Behavior of Agbelouve Silty Sand Stabilized with Cement Used as a Roadway Layer in Southern Togo
Abalo P’kla,
Yawovi Mawuénya Xolali Dany Ayité
Issue:
Volume 8, Issue 3, September 2019
Pages:
127-131
Received:
17 August 2019
Accepted:
5 September 2019
Published:
19 September 2019
Abstract: Silty or slimy sand stabilized with cement is used as a base or foundation layer when good quality natural materials are not available nearby. However, its mechanical characteristics are far from being mastered. In this paper, mechanical characteristics at different ages of silty sand stabilized with cement at different rates are studied. For this, specimen of silty sand stabilized with cement at rates of 2.5, 3.5 and 4.5% are subjected to the Modified Proctor test and to the compressive and tensile strength tests at 7, 28, 60, 90 and 360 days of age. The results show that compressive and tensile strengths increase with age and cement rate. The study of the different correlations between the resistances allowed the theoretical estimation of the parameters of roadway dimensioning in particular the fatigue resistance under a million loading cycles and the design fatigue resistance.
Abstract: Silty or slimy sand stabilized with cement is used as a base or foundation layer when good quality natural materials are not available nearby. However, its mechanical characteristics are far from being mastered. In this paper, mechanical characteristics at different ages of silty sand stabilized with cement at different rates are studied. For this,...
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Influence of Nitrogen Ion Implantation on the Disc Brake Material of Motor Vehicles Component
Bangun Pribadi,
Emy Mulyani,
Tjipto Sujitno
Issue:
Volume 8, Issue 3, September 2019
Pages:
132-136
Received:
22 July 2019
Accepted:
16 September 2019
Published:
29 September 2019
Abstract: Weaknesses of local disc brakes are cover several conditions such as low hardness, wear, and corrosion resistance. To improve this weakness, it is necessary to modify the surface properties of the material. The aim of this research is to study the influences of nitrogen ion implantation on the surface properties of a disc brake material. The implantation process was carried out for various of ions dose such as 3.107×1016 ions/cm2, 3.148×1016 ions/cm2, 3.728×1016 ions/cm2, 4.039×1016 ions/cm2, 4.350×1016 ions/cm2 at a certain energy and beam current of 60×1016 ions/cm2, 30 μA respectively. Hardness and wear properties were tested using microhardness tester and wear testing machine, respectively. Meanwhile, the crystalline structure for un-implanted (raw) and implanted materials at the optimum dose was analyzed using XRD. From the hardness test results, it can be obtained that the hardness of raw material is 59.82 VHN and after implantation it reached the highest value of 109.78 VHN or increases by factor 83%, while the wear test results is 22.9×10-9 mm2/kg for raw material and after implantation it reaches the highest value of 2.5×10-9 cm2/kg or decreases by factor 88%. These conditions were obtained at 3.728×1016 ions/cm2 of dose. Based on the XRD analysis, 45.5% Fe2N and 54.55% Fe3N compounds are formed.
Abstract: Weaknesses of local disc brakes are cover several conditions such as low hardness, wear, and corrosion resistance. To improve this weakness, it is necessary to modify the surface properties of the material. The aim of this research is to study the influences of nitrogen ion implantation on the surface properties of a disc brake material. The implan...
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