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Volume 40 (2022): Issue 2 (August 2022)

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Volume 39 (2021): Issue 4 (December 2021)

Volume 39 (2021): Issue 3 (September 2021)

Volume 39 (2021): Issue 2 (June 2021)

Volume 39 (2021): Issue 1 (March 2021)

Volume 38 (2020): Issue 4 (December 2020)

Volume 38 (2020): Issue 3 (September 2020)

Volume 38 (2020): Issue 2 (June 2020)

Volume 38 (2020): Issue 1 (March 2020)

Volume 37 (2019): Issue 4 (December 2019)

Volume 37 (2019): Issue 3 (September 2019)

Volume 37 (2019): Issue 2 (June 2019)

Volume 37 (2019): Issue 1 (March 2019)

Volume 36 (2018): Issue 4 (December 2018)

Volume 36 (2018): Issue 3 (September 2018)

Volume 36 (2018): Issue 2 (June 2018)

Volume 36 (2018): Issue 1 (March 2018)

Volume 35 (2017): Issue 4 (December 2017)

Volume 35 (2017): Issue 3 (October 2017)

Volume 35 (2017): Issue 2 (July 2017)

Volume 35 (2017): Issue 1 (March 2017)

Volume 34 (2016): Issue 4 (December 2016)

Volume 34 (2016): Issue 3 (September 2016)

Volume 34 (2016): Issue 2 (June 2016)

Volume 34 (2016): Issue 1 (March 2016)

Volume 33 (2015): Issue 4 (December 2015)

Volume 33 (2015): Issue 3 (September 2015)

Volume 33 (2015): Issue 2 (June 2015)

Volume 33 (2015): Issue 1 (March 2015)

Volume 32 (2014): Issue 4 (December 2014)

Volume 32 (2014): Issue 3 (September 2014)

Volume 32 (2014): Issue 2 (June 2014)

Volume 32 (2014): Issue 1 (January 2014)

Volume 31 (2013): Issue 4 (October 2013)

Volume 31 (2013): Issue 3 (August 2013)

Volume 31 (2013): Issue 2 (April 2013)

Volume 31 (2013): Issue 1 (January 2013)

Volume 30 (2012): Issue 4 (December 2012)

Volume 30 (2012): Issue 3 (September 2012)

Volume 30 (2012): Issue 2 (June 2012)

Volume 30 (2012): Issue 1 (March 2012)

Volume 29 (2011): Issue 4 (December 2011)

Volume 29 (2011): Issue 3 (September 2011)

Volume 29 (2011): Issue 2 (June 2011)

Volume 29 (2011): Issue 1 (March 2011)

Journal Details
Format
Journal
eISSN
2083-134X
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

Volume 39 (2021): Issue 1 (March 2021)

Journal Details
Format
Journal
eISSN
2083-134X
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

12 Articles
access type Open Access

Finite element modeling of continuous drive friction welding of Al6061 alloy

Published Online: 30 May 2021
Page range: 1 - 14

Abstract

Abstract

Continuous drive friction welding process is widely used in various industrial applications to assemble shafts, tubes, and many other components. This paper's motivation was developing a CDFW model using the Finite Element Method (FEM). The coupling of the process's thermal and mechanical behaviors was considered during the simulation by COMSOL Multiphysics®. The construction of phase transition curves for Al6061 allowed determining several temperature-dependent thermophysical properties of the material. These properties are then injected in a second simulation to study the temperature evolution during welding. Subsequently, these results are compared and analyzed with the experimental outcomes. Excellent comparability between the model and experimental results was achieved. A unique phenomenon in the welding temperature profile was observed and explained through the model and experimental results interpretation.

Keywords

  • Continuous drive friction welding
  • FEM
  • COMSOL
  • aluminum 6061
access type Open Access

Transport and magnetic properties of Bi(Pb)2212 superconducting ceramics doped by low rate of potassium

Published Online: 01 Jun 2021
Page range: 15 - 23

Abstract

Abstract

Samples of Bi1.5Pb0.5(Sr1.8−xKx)CaCu2O8+d and Bi1.5Pb0.5Sr1.8CaCu2O8+dKx have been prepared from powders of carbonates and primary oxides using the solid state reaction method and compared in this study. In the first case, potassium (K) is substituted in the strontium (Sr) site. In the second one, K is added. A part of the paper is devoted to discuss the results obtained by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) observations of (Bi,Pb)2Sr1.8CaCu2O8+d samples doped by potassium to provide additional microstructural information related to the doping method. These analyses are supplemented by resistivity and magnetic measurements. Results show how the rate of doping by potassium affects transport and magnetic properties of Bi(Pb)2212 phase. The critical current density (Jc) is improved using the two methods and it reaches a double value by the addition of K as compared to the undoped sample.

Keywords

  • ceramics
  • superconductors
  • transport properties
  • magnetic properties
access type Open Access

Spinel zinc ferrite nanostructured thin-films for enhanced light-harvesting in polycrystalline solar cells

Published Online: 08 Jun 2021
Page range: 24 - 32

Abstract

Abstract

Spinel zinc ferrite (ZnFe2O4) nanocrystallites are applied as an anti-reflection coating (ARC) for the enhanced light harvesting in polycrystalline silicon solar cells (PCSSC) and its effect were studied. Spinel zinc ferrite nanocrystallites were prepared using precursors of zinc and ferric chloride by co-precipitation method. The morphological, optical, electrical characterizations are comprehensively used to establish the performance of spinel ZnFe2O4 Nanostructured Thin Films (NTF) covered and uncovered PCSSC. Further, X-ray diffraction and fluorescence analysis have been performed to demonstrate the crystallographic patterns and elemental compositions of ZnFe2O4 nanocrystallites. The developed spinel ZnFe2O4 NTF on PCSSC shows the reduction in reflectivity (20.3%), improvement in light trapping efficiency (17.5%) and transmittance of the fabricated spinel ZnFe2O4 NTF was validated with optical and electrical observations.

Keywords

  • Spinel zinc ferrite nanocrystallites
  • nanostructured thin films
  • light-harvesting and anti-reflection coating
  • polycrystalline silicon solar cells
access type Open Access

Stimulated autogenous-healing capacity of fiber-reinforced mortar incorporating healing agents for recovery against fracture and mechanical properties

Published Online: 26 Jun 2021
Page range: 33 - 48

Abstract

Abstract

This study aimed to investigate the effect of autogenous healing capacity with the addition of expansive and crystalline agents on mechanical and fracture behaviors of fiber-reinforced (FR) mortar specimens with crack mouth opening displacement (CMOD) controlled test set-up. The experimental results of a self-healing approach of FR mortar were analyzed in terms of first cracking peak load (FCPL) increase, index of fracture toughness recovery (IFTR), and index of fracture energy recovery (IFER). Initially, the specimens were pre-cracked at different crack widths ranging from 30 μm to 200 μm after 28-days of curing. After pre-cracking, the specimens were kept in water for 56- and 120-day healing. A controlled three-point bending test (PBT) was applied on prism specimen having a central notch of 40 mm depth for pre-cracking as well as the post-conditioning stage for determining the FCPL. However, the crack surfaces were monitored by a high-range digital microscope and scanning electron microscope (SEM) to examine the nature of healed products near the damaged area. Test results revealed that a significant recovery of small cracks (≤50 μm) could be achieved for self-healing specimens by using healing agents (HA), while for large cracks (≥100 μm) partial recovery could be achieved after the 120-day healing period.

Keywords

  • self-healing
  • crack width
  • fracture properties
  • mechanical properties
  • mortar
access type Open Access

Study on factors of interface properties of axial braided C/C composite materials

Published Online: 02 Jul 2021
Page range: 49 - 58

Abstract

Abstract

In order to study the influencing factors of the tensile properties of axial braided C/C composites, the interfacial shear strength of the fiber rod and matrix was studied and ejecting tests of the fiber rod were carried out. The ejecting test specimens were formed with different thicknesses to obtain the changing rule of the interface shear strength with the thickness of the sample, and the testing method for the interface shear strength of the axial braided C/C composite material. The results show that the recommended thickness of the ejecting test specimens for the interface shear strength of is four times the diameter of the fiber rod. The interface shear strength distribution law of two different batches of materials was obtained through the interface ejecting test. The mesoscopic structure characteristics and pore statistical distribution law of the hole surface after ejecting were analyzed by scanning electron microscopy (SEM), and the mechanism of the difference of the interface shear strength was obtained. The tensile properties of two different batches of materials were obtained by tensile tests. The results show that the tensile properties of the two batches of materials differ greatly. The analysis suggests that the reason for this difference is the differences in interfacial bonding strength between the fiber rod and matrix. The higher the interface shear strength, the better the tensile property of the material will be.

Keywords

  • interface properties
  • axial braided C/C
  • porosity scale
  • interface shear strength
access type Open Access

A study on the mixed properties of green controlled low strength cementitious

Published Online: 06 Jul 2021
Page range: 59 - 74

Abstract

Abstract

In this study, two industrial wastes – circulating fluidized bed combustion co-fired fly ash (CFA) and ground granulated blast-furnace slag (GGBS) – were used as green materials instead of cementitious materials in controllable low strength material (CLSM). CLSM was used to backfill the pavement. CLSM should meet the compressive strength requirements of the CLSM specification (under 8.24 MPa), and it had the self-consolidating characteristics of fluidized concrete. In order to comply with the characteristics of self-consolidation, a mix design including superplasticizers, adhesives, and accelerators were used to ensure that the proportion could meet the requirements of both CLSM and the self-consolidating properties. The test methods included the slump flow test, ball drop test, strength activity index, compressive strength, mercury intrusion porosimetry, chlo-ride migration test, and scanning electron microscope. A water/cement ratio of 0.85 was used as the mix design for the CLSM requirements. The CFA and GGBS used in CLSM could replace 78 wt.% of the cement, and CLSM could effectively meet the requirements of the workability, strength and microscopic properties.

Keywords

  • Co-fired fly ash
  • ground granulated blast-furnace slag
  • controlled low strength materials
  • self-consolidating concrete
  • green materials
access type Open Access

The impact of changes in pore structure on the compressive strength of sulphoaluminate cement concrete at high temperature

Published Online: 06 Jul 2021
Page range: 75 - 85

Abstract

Abstract

The internal pore structure of sulphoaluminate cement concrete (SACC) significantly affects its mechanical properties. The main purpose of this study was to establish the relationship between pore structure changes and compressive strength after exposure to elevated temperatures. SACC samples that had been cured for 12 months were dried to a constant weight and then exposed to different temperatures (100 °C, 200 °C and 300 °C), after which the compressive strength and pore structure were measured. The pore structure of SACC was quantitatively described by mercury intrusion porosimetry (MIP) and nitrogen adsorption results. The results showed that with increased temperature, the porosity of the SACC samples also increased and the pore structure was gradually destroyed. Moreover, the SACC’s compressive strength gradually decreased with increasing temperature. The relationship between compressive strength and porosity was in close agreement with the compressive strength–porosity equation proposed by Schiller. Therefore, after extensive exposure to elevated temperature, the changes in SACC’s compressive strength can be quantitatively described by the Schiller equation.

Keywords

  • Elevated temperature
  • pore structure
  • sulphoaluminate cement concrete
  • mercury intrusion porosimetry (MIP)
  • nitrogen adsorption
access type Open Access

Analysis of the static and dynamic properties of wear-resistant Hardox 600 steel in the context of its application in working elements

Published Online: 06 Jul 2021
Page range: 86 - 102

Abstract

Abstract

The article discusses the static and dynamic properties of high-strength, boron-containing Hardox 600 steel that is resistant to abrasive wear, both in its delivery state and after normalization. Since the available published material in the literature does not have any real mechanical indicators of the abovementioned steel, a static tension test was carried out at an ambient temperature. The steel’s tensile strength, yield strength, Young’s modulus, elongation and reduction of area were determined from the test. The Charpy impact test at temperatures of −40 °C, −20 °C, 0 °C, and +20 °C and fractographic analysis were performed to determine the transition temperature of ductility to brittleness. In dynamic load conditions, the assigned values of impact energy do not always truly determine the material behavior. Thus, the aim of the fractography was to provide precision when determining the behavior. A significant difference in the impact energy of the tested steel with respect to its heat treatment and ductile-brittle transition temperature was observed and determined based on the impact test result, as well as the nature of the fracture. On the basis of the determined structural and strength characteristics, an analysis of the possibility of application of Hardox 600 steel on selected elements of working machines was performed.

Keywords

  • martensitic boron steel
  • steel resistant to abrasive wear
  • mechanical properties
  • structures
  • ductile to brittle transition temperature
  • fractographic analysis
access type Open Access

Effect of heat treatment on the microstructure and mechanical properties of a low-carbon X80 pipeline steel

Published Online: 09 Jul 2021
Page range: 103 - 112

Abstract

Abstract

In this work, the effect of heat treatment conditions on the microstructure and mechanical properties of an American Petroleum Institute (API) X80 steel with a low carbon content of ~0.02% wt., destined for the manufacture of pipelines and pipeline transmission systems by welding, was investigated. Samples were heat treated under different conditions and then were characterized by scanning electron microscopy (SEM), orientation image microscopy (OIM), and electron backscattered diffraction (EBSD). The results showed that when the steel is fastly cooled from the austenitic field (990°C), the mechanical properties increase significantly [ultimate tensile strength (UTS) >1,100 MPa, yield strength (YS) 900 MPa, and elongation 27%] due to the high percentage of martensite (M) present in the microstructure (95%). In contrast, when the cooling rate decreases and the treatment conditions remain at/or above the bainitic/martensitic transformation (from 990°C to 600°C and 450°C), the mechanical properties are decreased by almost 50% because of the decrease in the percentage of martensite (18%). However, the percentage of elongation increases significantly (38%) due to the presence of other micro-constituents resulting from the phase transformation. On the other hand, the best combination of mechanical properties (UTS above 800 MPa and YS between 610 MPa and 720 MPa) was obtained when the steel acquired a dual-phase microstructure [(martensite/austenite)-(ferrite/martensite)] since the amount of martensite is conserved between 45% and 82%, in combination with the other micro-constituent present in the steel that allows us to achieve elongation percentages close to 30%.

Keywords

  • X80 steel
  • microstructure
  • mechanical properties
  • IQ
  • EBSD
access type Open Access

Formability of laser welded steel/magnesium dissimilar metal with Sn powder-adhesive interlayer

Published Online: 09 Jul 2021
Page range: 113 - 123

Abstract

Abstract

The exploratory experiments of laser fusion welding with Sn powder and the automotive adhesive addition were conducted for DP590 dual-phase steel and AZ31B magnesium alloy in an overlap steel-on-magnesium configuration. The characteristics of metal vapor/plasma were analyzed by collecting and analyzing plasma shape and welding spectra. The microstructure of the welded was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS). The temperature field distribution of the joint was simulated by COMSOL finite-element software. The results showed that the transfer of heat from steel to the magnesium alloy is hindered by the adhesive layer, which is conducive to the simultaneous melting of steel and magnesium with large differences in melting and boiling points. In addition, the width of the molten pool increases, but the depth is shallow on the magnesium side. Meanwhile, the recoil pressure induced by the splashing of the molten pool reduces, and the surface quality of the weld is improved. Some intermetallic compounds (IMCs), such as FeSn, Fe1.3Sn, and Fe3Sn, are formed inside the molten pool, while columnar dendrite Mg2Sn phase is also produced. The presence of these phases helps realize the bidirectional metallurgical bonding of steel/magnesium dissimilar metals.

Keywords

  • dissimilar metal welding
  • micro-structure
  • numerical simulation
  • Sn-adhesive interlayer
access type Open Access

Experimental investigation of the electrochemical micromachining process of Ti-6Al-4V titanium alloy under the influence of magnetic field

Published Online: 09 Jul 2021
Page range: 124 - 138

Abstract

Abstract

An attempt has been made to study the influence of magnetic field on the micro hole machining of Ti-6Al-4V titanium alloy using electrochemical micromachining (ECMM) process. The presence of magneto hydro dynamics (MHD) is accomplished with the aid of external magnetic field (neodymium magnets) in order to improve the machining accuracy and the performance characteristics of ECMM. Close to ideal solution for magnetic and nonmagnetic field ECMM process, the parameters used are as follows: concentration electrolyte of 15 g/l; peak current of 1.35 A; pulse on time of 400 s; and duty factor of 0.5. An improvement of 11.91–52.43% and 23.51–129.68% in material removal rate (MRR) and 6.03–21.47% and 18.32–33.09% in overcut (OC) is observed in ECMM of titanium alloy under the influence of attraction and repulsion magnetic field, respectively, in correlation with nonmagnetic field ECMM process. A 55.34% surface roughness factor reduction is ascertained in the hole profile in magnetic field-ECMM in correlation with electrochemical machined titanium alloy under nonmagnetic field environment. No machining related stress is induced in the titanium alloy, even though environment of electrochemical machining process has been enhanced with the presence of magnetic field. A slight surge in the compressive residual factor, aids in surge of passivation potential of titanium alloy, resulting in higher resistance to outside environment.

Keywords

  • ECMM
  • machining
  • magnetic
  • overcut
  • roughness
  • titanium
access type Open Access

Influence of zinc substitution on structural, elastic, magnetic and optical properties of cobalt chromium ferrites

Published Online: 16 Jul 2021
Page range: 139 - 151

Abstract

Abstract

The polycrystalline Co1−xZnxCr0.5Fe1.5O4 series with (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) has been synthesized by conventional ceramic rout method. The structural and elastic properties have been investigated by X-ray diffractometer and Fourier transform spectroscopy. Both XRD and FTIR confirm the formation of single phase cubic spinel ferrites. The cationic distribution for all samples has been proposed. The lattice parameter, X-ray density, hoping length, bond length, and packing factors–in accompaniment with variations in the zinc concentration–have been studied. The IR band position has been explained by the cations involved in the structure. The elastic moduli such as Young's modulus, bulk modulus, rigidity modulus and Poison's ratio have bee calculated using force constants. Scanning electron microscope (SEM) observation conveys information about the agglomeration of particles. The hysteresis curve obtained from vibrating sample magneto meter (VSM) conveys information about the soft nature of prepared compositions. The saturation magnetization decreases with addition of zinc ions and coercivity is almost zero. An increase in band gap energy has been observed with addition of zinc by Ultraviolet Visible Spectroscopy (UV-VIS), which is due to small crystallite size.

Keywords

  • cationic distribution
  • force constant
  • dielectric constant
  • aglomeration
12 Articles
access type Open Access

Finite element modeling of continuous drive friction welding of Al6061 alloy

Published Online: 30 May 2021
Page range: 1 - 14

Abstract

Abstract

Continuous drive friction welding process is widely used in various industrial applications to assemble shafts, tubes, and many other components. This paper's motivation was developing a CDFW model using the Finite Element Method (FEM). The coupling of the process's thermal and mechanical behaviors was considered during the simulation by COMSOL Multiphysics®. The construction of phase transition curves for Al6061 allowed determining several temperature-dependent thermophysical properties of the material. These properties are then injected in a second simulation to study the temperature evolution during welding. Subsequently, these results are compared and analyzed with the experimental outcomes. Excellent comparability between the model and experimental results was achieved. A unique phenomenon in the welding temperature profile was observed and explained through the model and experimental results interpretation.

Keywords

  • Continuous drive friction welding
  • FEM
  • COMSOL
  • aluminum 6061
access type Open Access

Transport and magnetic properties of Bi(Pb)2212 superconducting ceramics doped by low rate of potassium

Published Online: 01 Jun 2021
Page range: 15 - 23

Abstract

Abstract

Samples of Bi1.5Pb0.5(Sr1.8−xKx)CaCu2O8+d and Bi1.5Pb0.5Sr1.8CaCu2O8+dKx have been prepared from powders of carbonates and primary oxides using the solid state reaction method and compared in this study. In the first case, potassium (K) is substituted in the strontium (Sr) site. In the second one, K is added. A part of the paper is devoted to discuss the results obtained by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) observations of (Bi,Pb)2Sr1.8CaCu2O8+d samples doped by potassium to provide additional microstructural information related to the doping method. These analyses are supplemented by resistivity and magnetic measurements. Results show how the rate of doping by potassium affects transport and magnetic properties of Bi(Pb)2212 phase. The critical current density (Jc) is improved using the two methods and it reaches a double value by the addition of K as compared to the undoped sample.

Keywords

  • ceramics
  • superconductors
  • transport properties
  • magnetic properties
access type Open Access

Spinel zinc ferrite nanostructured thin-films for enhanced light-harvesting in polycrystalline solar cells

Published Online: 08 Jun 2021
Page range: 24 - 32

Abstract

Abstract

Spinel zinc ferrite (ZnFe2O4) nanocrystallites are applied as an anti-reflection coating (ARC) for the enhanced light harvesting in polycrystalline silicon solar cells (PCSSC) and its effect were studied. Spinel zinc ferrite nanocrystallites were prepared using precursors of zinc and ferric chloride by co-precipitation method. The morphological, optical, electrical characterizations are comprehensively used to establish the performance of spinel ZnFe2O4 Nanostructured Thin Films (NTF) covered and uncovered PCSSC. Further, X-ray diffraction and fluorescence analysis have been performed to demonstrate the crystallographic patterns and elemental compositions of ZnFe2O4 nanocrystallites. The developed spinel ZnFe2O4 NTF on PCSSC shows the reduction in reflectivity (20.3%), improvement in light trapping efficiency (17.5%) and transmittance of the fabricated spinel ZnFe2O4 NTF was validated with optical and electrical observations.

Keywords

  • Spinel zinc ferrite nanocrystallites
  • nanostructured thin films
  • light-harvesting and anti-reflection coating
  • polycrystalline silicon solar cells
access type Open Access

Stimulated autogenous-healing capacity of fiber-reinforced mortar incorporating healing agents for recovery against fracture and mechanical properties

Published Online: 26 Jun 2021
Page range: 33 - 48

Abstract

Abstract

This study aimed to investigate the effect of autogenous healing capacity with the addition of expansive and crystalline agents on mechanical and fracture behaviors of fiber-reinforced (FR) mortar specimens with crack mouth opening displacement (CMOD) controlled test set-up. The experimental results of a self-healing approach of FR mortar were analyzed in terms of first cracking peak load (FCPL) increase, index of fracture toughness recovery (IFTR), and index of fracture energy recovery (IFER). Initially, the specimens were pre-cracked at different crack widths ranging from 30 μm to 200 μm after 28-days of curing. After pre-cracking, the specimens were kept in water for 56- and 120-day healing. A controlled three-point bending test (PBT) was applied on prism specimen having a central notch of 40 mm depth for pre-cracking as well as the post-conditioning stage for determining the FCPL. However, the crack surfaces were monitored by a high-range digital microscope and scanning electron microscope (SEM) to examine the nature of healed products near the damaged area. Test results revealed that a significant recovery of small cracks (≤50 μm) could be achieved for self-healing specimens by using healing agents (HA), while for large cracks (≥100 μm) partial recovery could be achieved after the 120-day healing period.

Keywords

  • self-healing
  • crack width
  • fracture properties
  • mechanical properties
  • mortar
access type Open Access

Study on factors of interface properties of axial braided C/C composite materials

Published Online: 02 Jul 2021
Page range: 49 - 58

Abstract

Abstract

In order to study the influencing factors of the tensile properties of axial braided C/C composites, the interfacial shear strength of the fiber rod and matrix was studied and ejecting tests of the fiber rod were carried out. The ejecting test specimens were formed with different thicknesses to obtain the changing rule of the interface shear strength with the thickness of the sample, and the testing method for the interface shear strength of the axial braided C/C composite material. The results show that the recommended thickness of the ejecting test specimens for the interface shear strength of is four times the diameter of the fiber rod. The interface shear strength distribution law of two different batches of materials was obtained through the interface ejecting test. The mesoscopic structure characteristics and pore statistical distribution law of the hole surface after ejecting were analyzed by scanning electron microscopy (SEM), and the mechanism of the difference of the interface shear strength was obtained. The tensile properties of two different batches of materials were obtained by tensile tests. The results show that the tensile properties of the two batches of materials differ greatly. The analysis suggests that the reason for this difference is the differences in interfacial bonding strength between the fiber rod and matrix. The higher the interface shear strength, the better the tensile property of the material will be.

Keywords

  • interface properties
  • axial braided C/C
  • porosity scale
  • interface shear strength
access type Open Access

A study on the mixed properties of green controlled low strength cementitious

Published Online: 06 Jul 2021
Page range: 59 - 74

Abstract

Abstract

In this study, two industrial wastes – circulating fluidized bed combustion co-fired fly ash (CFA) and ground granulated blast-furnace slag (GGBS) – were used as green materials instead of cementitious materials in controllable low strength material (CLSM). CLSM was used to backfill the pavement. CLSM should meet the compressive strength requirements of the CLSM specification (under 8.24 MPa), and it had the self-consolidating characteristics of fluidized concrete. In order to comply with the characteristics of self-consolidation, a mix design including superplasticizers, adhesives, and accelerators were used to ensure that the proportion could meet the requirements of both CLSM and the self-consolidating properties. The test methods included the slump flow test, ball drop test, strength activity index, compressive strength, mercury intrusion porosimetry, chlo-ride migration test, and scanning electron microscope. A water/cement ratio of 0.85 was used as the mix design for the CLSM requirements. The CFA and GGBS used in CLSM could replace 78 wt.% of the cement, and CLSM could effectively meet the requirements of the workability, strength and microscopic properties.

Keywords

  • Co-fired fly ash
  • ground granulated blast-furnace slag
  • controlled low strength materials
  • self-consolidating concrete
  • green materials
access type Open Access

The impact of changes in pore structure on the compressive strength of sulphoaluminate cement concrete at high temperature

Published Online: 06 Jul 2021
Page range: 75 - 85

Abstract

Abstract

The internal pore structure of sulphoaluminate cement concrete (SACC) significantly affects its mechanical properties. The main purpose of this study was to establish the relationship between pore structure changes and compressive strength after exposure to elevated temperatures. SACC samples that had been cured for 12 months were dried to a constant weight and then exposed to different temperatures (100 °C, 200 °C and 300 °C), after which the compressive strength and pore structure were measured. The pore structure of SACC was quantitatively described by mercury intrusion porosimetry (MIP) and nitrogen adsorption results. The results showed that with increased temperature, the porosity of the SACC samples also increased and the pore structure was gradually destroyed. Moreover, the SACC’s compressive strength gradually decreased with increasing temperature. The relationship between compressive strength and porosity was in close agreement with the compressive strength–porosity equation proposed by Schiller. Therefore, after extensive exposure to elevated temperature, the changes in SACC’s compressive strength can be quantitatively described by the Schiller equation.

Keywords

  • Elevated temperature
  • pore structure
  • sulphoaluminate cement concrete
  • mercury intrusion porosimetry (MIP)
  • nitrogen adsorption
access type Open Access

Analysis of the static and dynamic properties of wear-resistant Hardox 600 steel in the context of its application in working elements

Published Online: 06 Jul 2021
Page range: 86 - 102

Abstract

Abstract

The article discusses the static and dynamic properties of high-strength, boron-containing Hardox 600 steel that is resistant to abrasive wear, both in its delivery state and after normalization. Since the available published material in the literature does not have any real mechanical indicators of the abovementioned steel, a static tension test was carried out at an ambient temperature. The steel’s tensile strength, yield strength, Young’s modulus, elongation and reduction of area were determined from the test. The Charpy impact test at temperatures of −40 °C, −20 °C, 0 °C, and +20 °C and fractographic analysis were performed to determine the transition temperature of ductility to brittleness. In dynamic load conditions, the assigned values of impact energy do not always truly determine the material behavior. Thus, the aim of the fractography was to provide precision when determining the behavior. A significant difference in the impact energy of the tested steel with respect to its heat treatment and ductile-brittle transition temperature was observed and determined based on the impact test result, as well as the nature of the fracture. On the basis of the determined structural and strength characteristics, an analysis of the possibility of application of Hardox 600 steel on selected elements of working machines was performed.

Keywords

  • martensitic boron steel
  • steel resistant to abrasive wear
  • mechanical properties
  • structures
  • ductile to brittle transition temperature
  • fractographic analysis
access type Open Access

Effect of heat treatment on the microstructure and mechanical properties of a low-carbon X80 pipeline steel

Published Online: 09 Jul 2021
Page range: 103 - 112

Abstract

Abstract

In this work, the effect of heat treatment conditions on the microstructure and mechanical properties of an American Petroleum Institute (API) X80 steel with a low carbon content of ~0.02% wt., destined for the manufacture of pipelines and pipeline transmission systems by welding, was investigated. Samples were heat treated under different conditions and then were characterized by scanning electron microscopy (SEM), orientation image microscopy (OIM), and electron backscattered diffraction (EBSD). The results showed that when the steel is fastly cooled from the austenitic field (990°C), the mechanical properties increase significantly [ultimate tensile strength (UTS) >1,100 MPa, yield strength (YS) 900 MPa, and elongation 27%] due to the high percentage of martensite (M) present in the microstructure (95%). In contrast, when the cooling rate decreases and the treatment conditions remain at/or above the bainitic/martensitic transformation (from 990°C to 600°C and 450°C), the mechanical properties are decreased by almost 50% because of the decrease in the percentage of martensite (18%). However, the percentage of elongation increases significantly (38%) due to the presence of other micro-constituents resulting from the phase transformation. On the other hand, the best combination of mechanical properties (UTS above 800 MPa and YS between 610 MPa and 720 MPa) was obtained when the steel acquired a dual-phase microstructure [(martensite/austenite)-(ferrite/martensite)] since the amount of martensite is conserved between 45% and 82%, in combination with the other micro-constituent present in the steel that allows us to achieve elongation percentages close to 30%.

Keywords

  • X80 steel
  • microstructure
  • mechanical properties
  • IQ
  • EBSD
access type Open Access

Formability of laser welded steel/magnesium dissimilar metal with Sn powder-adhesive interlayer

Published Online: 09 Jul 2021
Page range: 113 - 123

Abstract

Abstract

The exploratory experiments of laser fusion welding with Sn powder and the automotive adhesive addition were conducted for DP590 dual-phase steel and AZ31B magnesium alloy in an overlap steel-on-magnesium configuration. The characteristics of metal vapor/plasma were analyzed by collecting and analyzing plasma shape and welding spectra. The microstructure of the welded was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS). The temperature field distribution of the joint was simulated by COMSOL finite-element software. The results showed that the transfer of heat from steel to the magnesium alloy is hindered by the adhesive layer, which is conducive to the simultaneous melting of steel and magnesium with large differences in melting and boiling points. In addition, the width of the molten pool increases, but the depth is shallow on the magnesium side. Meanwhile, the recoil pressure induced by the splashing of the molten pool reduces, and the surface quality of the weld is improved. Some intermetallic compounds (IMCs), such as FeSn, Fe1.3Sn, and Fe3Sn, are formed inside the molten pool, while columnar dendrite Mg2Sn phase is also produced. The presence of these phases helps realize the bidirectional metallurgical bonding of steel/magnesium dissimilar metals.

Keywords

  • dissimilar metal welding
  • micro-structure
  • numerical simulation
  • Sn-adhesive interlayer
access type Open Access

Experimental investigation of the electrochemical micromachining process of Ti-6Al-4V titanium alloy under the influence of magnetic field

Published Online: 09 Jul 2021
Page range: 124 - 138

Abstract

Abstract

An attempt has been made to study the influence of magnetic field on the micro hole machining of Ti-6Al-4V titanium alloy using electrochemical micromachining (ECMM) process. The presence of magneto hydro dynamics (MHD) is accomplished with the aid of external magnetic field (neodymium magnets) in order to improve the machining accuracy and the performance characteristics of ECMM. Close to ideal solution for magnetic and nonmagnetic field ECMM process, the parameters used are as follows: concentration electrolyte of 15 g/l; peak current of 1.35 A; pulse on time of 400 s; and duty factor of 0.5. An improvement of 11.91–52.43% and 23.51–129.68% in material removal rate (MRR) and 6.03–21.47% and 18.32–33.09% in overcut (OC) is observed in ECMM of titanium alloy under the influence of attraction and repulsion magnetic field, respectively, in correlation with nonmagnetic field ECMM process. A 55.34% surface roughness factor reduction is ascertained in the hole profile in magnetic field-ECMM in correlation with electrochemical machined titanium alloy under nonmagnetic field environment. No machining related stress is induced in the titanium alloy, even though environment of electrochemical machining process has been enhanced with the presence of magnetic field. A slight surge in the compressive residual factor, aids in surge of passivation potential of titanium alloy, resulting in higher resistance to outside environment.

Keywords

  • ECMM
  • machining
  • magnetic
  • overcut
  • roughness
  • titanium
access type Open Access

Influence of zinc substitution on structural, elastic, magnetic and optical properties of cobalt chromium ferrites

Published Online: 16 Jul 2021
Page range: 139 - 151

Abstract

Abstract

The polycrystalline Co1−xZnxCr0.5Fe1.5O4 series with (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) has been synthesized by conventional ceramic rout method. The structural and elastic properties have been investigated by X-ray diffractometer and Fourier transform spectroscopy. Both XRD and FTIR confirm the formation of single phase cubic spinel ferrites. The cationic distribution for all samples has been proposed. The lattice parameter, X-ray density, hoping length, bond length, and packing factors–in accompaniment with variations in the zinc concentration–have been studied. The IR band position has been explained by the cations involved in the structure. The elastic moduli such as Young's modulus, bulk modulus, rigidity modulus and Poison's ratio have bee calculated using force constants. Scanning electron microscope (SEM) observation conveys information about the agglomeration of particles. The hysteresis curve obtained from vibrating sample magneto meter (VSM) conveys information about the soft nature of prepared compositions. The saturation magnetization decreases with addition of zinc ions and coercivity is almost zero. An increase in band gap energy has been observed with addition of zinc by Ultraviolet Visible Spectroscopy (UV-VIS), which is due to small crystallite size.

Keywords

  • cationic distribution
  • force constant
  • dielectric constant
  • aglomeration

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