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High-Strength Geopolymer Concrete- Properties, Advantages and Challenges
Kamal Neupane,
Des Chalmers,
Paul Kidd
Issue:
Volume 7, Issue 2, June 2018
Pages:
15-25
Received:
15 May 2018
Accepted:
1 June 2018
Published:
25 June 2018
Abstract: Geopolymer is a noble material, made from reaction between aluminosilicate compounds and alkali solution which owns a good binding property. In last decades, lots of research and development works have been carried out globally to investigate the engineering, thermal, micro-structural and durability properties of geopolymer concrete as a sustainable alternative to Portland cement. Results from previous works indicated that geopolymer concrete exhibited better mechanical strength and durability properties than ordinary Portland cement (OPC) concrete. Nowadays, high-strength concrete is increasingly used in major civil construction works, such as high-rise buildings and bridges because of its structural and economic benefits over normal-strength concrete. This paper reports the experimental results on engineering properties of high-strength geopolymer concretes of 65 and 80 MPa using geopolymer binders at ambient curing conditions. High-strength concrete produced in this study was able to set quickly in ambient conditions therefore can attain sufficient strength at early days as well as exhibited higher tensile and flexural strength than concrete from OPC. High-strength geopolymer concrete can be produced with very simple mix design; however, it has some limitation for commercial applications. This paper discusses about the advantages and limitations of geopolymer high-strength concrete for its application in concrete industry.
Abstract: Geopolymer is a noble material, made from reaction between aluminosilicate compounds and alkali solution which owns a good binding property. In last decades, lots of research and development works have been carried out globally to investigate the engineering, thermal, micro-structural and durability properties of geopolymer concrete as a sustainabl...
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Characterization of A Novel FR4/AlN Printed Circuit Board of High Thermal Conductivity
Diancheng Qin,
Yonglong Xiao,
Kewei Liang
Issue:
Volume 7, Issue 2, June 2018
Pages:
26-33
Received:
14 May 2018
Accepted:
6 June 2018
Published:
29 June 2018
Abstract: High thermally conductive cuboid aluminum nitride block was used as reinforcement material to fill the FR4 matrix for the fabrication of a novel FR4/AlN PCB (Printed Circuit Board) with high thermal conductivity. This novel PCB was subjected to a thermal shock test of 1500 cycles from -40°C keeping 30 minutes to 125°C keeping 30 minutes during 1000 hours with transfer time less than 10 seconds, presented an excellent reliability since there was no crack and delamination emerging. By performing a comparative study between FR4/AlN PCB and anodized MCPCB, it was found that the thermal resistance of both PCB were 0.63°C /W and 2.74°C /W respectively. When CREE XTE LEDs were mounted on FR4/AlN PCB and anodized MCPCB using SMT technology to dissipate heat respectively, the LEDs’ junction temperature were 37°C and 42.1°C and the overall corresponding thermal resistance were 3.93°C /W and 6.43°C /W accordingly. Therefore, a conclusion can be drawn that this novel PCB exhibits a more excellent heat dissipation performance than 30W/m·K anodized MCPCB does and it is a promising alternative of MCPCB for heat dissipation of high power electronic devices like LEDs.
Abstract: High thermally conductive cuboid aluminum nitride block was used as reinforcement material to fill the FR4 matrix for the fabrication of a novel FR4/AlN PCB (Printed Circuit Board) with high thermal conductivity. This novel PCB was subjected to a thermal shock test of 1500 cycles from -40°C keeping 30 minutes to 125°C keeping 30 minutes during 1000...
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Simulation for Texture Formation of Both Face-Centered-Cubic Metals and Body-Centered-Cubic Ones Based on Rotational Symmetry among Principal Axes
Issue:
Volume 7, Issue 2, June 2018
Pages:
34-43
Received:
10 May 2018
Accepted:
30 May 2018
Published:
11 July 2018
Abstract: Based on the rotational symmetry of the principal axes of X [100], Y [010] and Z [001], in fcc metal 24 possible combinations of the five slips on {111} planes on <110> direction while in bcc metal 72 possible combinations of the five slips on {110} planes on <111> direction by intersection of two kinds of {110} planes from the three ones composed of {110}, {101} and {011} are respectively chosen both based on Taylor’s formidable restriction rule of the five slips. In fcc metal, orientation at onset (minimum) of Taylor factor M value, i.e. the minimum total slip amount, shows the cube {100}<001> and the M value gradually increases by way of {100}<001>→ {100}<016>→ {100}<013>→ {100}<012>→ {100}<023> → {100}<0,9,11> with decrease of φ1 or does {100}<001>→ {016}<100>→{013}<100> →{0,6,13}<100> with increase of φ2, most of which were experimentally reported as indiscrete recrystallized orientations with lowest dislocation density named the cluster composed of cube and cube-family in fcc metal. In bcc metal, crystal rotation is carried out by only one solution among the 72 by the minimum total slip amount at every strain and simulates properly lengthy of accumulated researcher’s experimental results such as the three stable orientations of bcc metal in rolling {112}<110>, {11 11 8}<44 11> and {100}<011>.
Abstract: Based on the rotational symmetry of the principal axes of X [100], Y [010] and Z [001], in fcc metal 24 possible combinations of the five slips on {111} planes on <110> direction while in bcc metal 72 possible combinations of the five slips on {110} planes on <111> direction by intersection of two kinds of {110} planes from the three ones composed of {110}, ...
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Effect of Pressure on Solidification Process and Mechanical Properties During Semi-Solid Casting by Computational Fluid Dynamics (CFD)
Nguyen Hong Hai,
Pham Quang
Issue:
Volume 7, Issue 2, June 2018
Pages:
44-49
Received:
17 June 2018
Accepted:
3 July 2018
Published:
31 July 2018
Abstract: This paper focused on the development of Computational Fluid Dynamics (CFD) by a mathematical model based on the control volume method, which would enable efficient simulation of the semi-solid processing of complex industrial casting parts. Theoretical basis of the numerical simulation was briefly introduced. The latent heat was incorporated using the effective specific heat. The mass, momentum and enthalpy transport equation for each phase were solved. The application of the model allowed determining the temperature fields in the metal and the mold at 1 sec and the liquid fraction at time step 0.15 s with three different pressure regimes. The calculated pressure distribution and the evolution of liquid fraction through the material were examined and used to clarify their influence further investigated with tensile and hardness testing.
Abstract: This paper focused on the development of Computational Fluid Dynamics (CFD) by a mathematical model based on the control volume method, which would enable efficient simulation of the semi-solid processing of complex industrial casting parts. Theoretical basis of the numerical simulation was briefly introduced. The latent heat was incorporated using...
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Mechanical and Reaction Properties of PTFE/Al/MnO2 Reactive Materials at Different Strain Rates
Junyi Huang,
Xiang Fang,
Yuchun Li,
Jiaxiang Wu,
Jiaxing Song
Issue:
Volume 7, Issue 2, June 2018
Pages:
50-57
Received:
9 August 2018
Published:
13 August 2018
Abstract: The mechanical responses of the PTFE/Al/MnO2 reactive material in the strain rate range of 10-3~4×103s-1 were studied by a universal testing machine and split Hopkinson pressure bar (SHPB) system, and the microstructure of PTFE/Al/MnO2 specimen was observed by Scanning Electron Microscope (SEM). Meanwhile, a standard drop-weight apparatus was used to reveal the reaction properties and impact sensitivity of the PTFE/Al/MnO2 reactive material. The results demonstrate that under quasi-static compression conditions, the yield strength and compressive strength of PTFE/Al/MnO2 specimens have obvious strain rate effects, while the elastic modulus and failure strain are insensitive to strain rate and remain almost unchanged. Under dynamic load conditions, the compressive strength of the PTFE/Al/MnO2 specimen has a linear relationship with the logarithm of the strain rate, while the critical strain and the logarithm of the strain rate show a parabolic relationship. The established constitutive equation can describe the mechanical behavior of PTFE/Al/MnO2 material at high strain rate well, which can provide a reference to the practical applications of the material. PAM specimens can react violently under the impact of a drop hammer, with intense light and a huge explosion sound. And the characteristic drop height of the PAM specimen was calculated as 58.13cm.
Abstract: The mechanical responses of the PTFE/Al/MnO2 reactive material in the strain rate range of 10-3~4×103s-1 were studied by a universal testing machine and split Hopkinson pressure bar (SHPB) system, and the microstructure of PTFE/Al/MnO2 specimen was observed by Scanning Electron Microscope (SEM). Meanwhile, a standard drop-weight apparatus was used ...
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As-cast Microstructures and Mechanical Properties of Mg-5Y-2Nd-xSm-0.5Zr (x= 0, 1, 3, 5) Magnesium Alloys
Gui Yunwei,
Li Quanan,
Chen Xiaoya,
Li Zhitao
Issue:
Volume 7, Issue 2, June 2018
Pages:
58-63
Received:
9 August 2018
Published:
13 August 2018
Abstract: The microstructures and mechanical properties of the as-cast Mg-5Y-2Nd-xSm-0.5Zr (x= 0, 1, 3, 5) alloys have been investigated by optical microscope (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) analysis, transmission electron microscopy (TEM), X-ray diffraction (XRD) and mechanical tensile test. The results show that all the as-cast alloys are mainly composed of α-Mg, Mg24Y5 and Mg41Nd5. After adding Sm, the alloy has a new phase of Mg41Sm5. Furthermore, grain gets refinement, the second phases gradually increase and the morphology of second phases transforms to continuous network distribution. In addition, the mechanical properties of the as-cast alloys vary with Sm content. With the increase of Sm, the ultimate tensile strength, yield strength and hardness of the alloy increase firstly and then decrease, and the elongation decreases. When the amount of Sm is 3%, the alloy has the best mechanical properties, and the ultimate tensile strength, yield strength, hardness and elongation are 245.9 MPa, 207.6 MPa, HV85.9 and 5.88%, respectively. The Mg-5Y-2Nd-0.5Zr alloy to which Sm is not added has a mixed fracture characteristic of ductile fracture and local cleavage fracture. In comparison, when the Sm is 3%, the tear surface of the fracture surface is fine and uniform, and there is no obvious secondary crack and a large dissociation surface, indicating that the fracture energy absorbs more energy, so it shows a high fracture. Strength and high elongation.
Abstract: The microstructures and mechanical properties of the as-cast Mg-5Y-2Nd-xSm-0.5Zr (x= 0, 1, 3, 5) alloys have been investigated by optical microscope (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) analysis, transmission electron microscopy (TEM), X-ray diffraction (XRD) and mechanical tensile test. The results show th...
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