The Experts below are selected from a list of 57189 Experts worldwide ranked by ideXlab platform
Sunghak Lee - One of the best experts on this subject based on the ideXlab platform.
-
dynamic tension compression asymmetry of martensitic transformation in austenitic fe 0 4 1 0 c 18mn steels for cryogenic applications
Acta Materialia, 2015Co-Authors: Hyunmin Kim, Nack J. Kim, Jaeyoung Park, Wooyeol Kim, Seok Su Sohn, Hyoung Seop Kim, Byeongjoo Lee, Sunghak LeeAbstract:Abstract In this study, cryogenic-temperature dynamic mechanical properties of austenitic Fe–(0.4, 1.0)C–18Mn steels were evaluated by conducting dynamic tensile and Compressive Tests, and deformation mechanisms including tension–compression asymmetry of martensitic transformation behavior were interpreted by microstructural evolution of dynamically tensioned or compressed specimens. After the dynamic tensile Test of the 0.4C–18Mn steel, the γ → ɛ → α ′ martensitic transformation occurred at −196 °C, whereas ɛ - or α ′-martensite was not found in the 1.0C–18Mn steel. After the dynamic Compressive Test, on the other hand, the γ → ɛ martensitic transformation occurred at −196 °C without the formation of α ′-martensites in the 0.4C–18Mn steel. This dynamic tensile-Compressive asymmetry of martensitic transformation was plausibly interpreted by austenite stability in relation with difference in molar volume, hydrostatic stress distribution, and adiabatic heating. The γ → α ′ transformation was prevented under the dynamic Compressive loading because the increase in molar volume was required for the γ → α ′ transformation, whereas it was promoted to induce the γ → ɛ → α ′ transformation under dynamic tensile loading.
-
interpretation of cryogenic temperature charpy fracture initiation and propagation energies by microstructural evolution occurring during dynamic Compressive Test of austenitic fe 0 4 1 0 c 18mn steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Hyunmin Kim, Jaeyoung Park, Seok Su Sohn, Joong Eun Jung, Sunghak LeeAbstract:In the present study, Charpy impact energy (ET) composed of fracture initiation energy (EI) and propagation energy (EP) of austenitic Fe–(0.4,1.0)C–18Mn steels was evaluated in the temperature range from room to cryogenic temperatures by an instrumented Charpy impact Tester, and was interpreted by microstructural evolution of dynamically compressed specimens. In the 1.0C–18Mn steel, the EI and EP decreased slightly with decreasing temperature, but the EP/ET ratio was kept to be about 0.5. In the 0.4C–18Mn steel, the EI remained almost constant or slightly decreased with decreasing temperature, while the EP/ET ratio steadily decreased, thereby leading to the lower (about 30%) cryogenic-temperature ET than that of the 1.0C–18Mn steel. Under the dynamic Compressive loading, a considerable number of e-martensites were formed in the 0.4C–18Mn steel, whereas they were not found in the 1.0C–18Mn steel, and their volume fractions increased steadily with decreasing temperature. This γ→e-martensite transformation was attributed to the decrease in stacking fault energy, and resulted in the very low EP and resultant ET.
-
effects of dynamic strain hardening exponent on abnormal cleavage fracture occurring during drop weight tear Test of api x70 and x80 linepipe steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2014Co-Authors: Minju Kang, Hyunmin Kim, Sunghak Lee, Sang Yong ShinAbstract:In this study, drop weight tear Tests (DWTT) were conducted on API X70 and X80 linepipe steels fabricated with various compositions and rolling and cooling conditions in order to correlate the strain hardening with the abnormal cleavage fracture occurring in the hammer-impacted area. Area fractions of fracture modes were measured from fractured DWTT specimens, and the measured data were analyzed in relation to microstructures, Charpy impact energy, and strain hardening. All the steels consisted of fine acicular ferrite, together with some bainitic ferrite, granular bainite, and martensite-austenite constituent. As the volume fraction of acicular ferrite increased, the area fraction of DWTT abnormal cleavage fracture decreased because the toughness of acicular ferrite was higher than other microstructures. The area fraction of abnormal cleavage fracture was weakly related with strain hardening exponents obtained from the quasi-static tensile and Compressive Tests, but showed better correlation with those obtained from the dynamic Compressive Test. This tendency could be more clearly observed when steels having similar Charpy impact energy levels were grouped. Since the DWTT was performed under a dynamic loading condition, thus, the abnormal cleavage fracture behavior should be related with the strain hardening analyzed under a dynamic loading condition.
-
Microstructure and Mechanical Properties of Two Continuous-Fiber-Reinforced Zr-Based Amorphous Alloy Composites Fabricated by Liquid Pressing Process
Metallurgical and Materials Transactions A, 2008Co-Authors: Sang-bok Lee, Sunghak Lee, Sang-kwan Lee, Nack J. KimAbstract:The feasibility to fabricate the tungsten and STS-fiber-reinforced amorphous alloy matrix composites was verified by analyses of the thermal stress and cooling behavior between matrix and metallic fibers. Approximately 50 to 65 vol pct of fibers were homogeneously distributed inside the amorphous matrix, although the matrix of the STS-fiber-reinforced composite contained a small amount of crystalline phases. The Compressive Test results indicated that the tungsten-fiber-reinforced composite was not fractured at one time after reaching the maximum Compressive strength of 2060 MPa, but showed some ductility as the Compressive load was sustained by fibers. The STS-fiber-reinforced composite showed the maximum strength of about 1050 MPa, and its strength maintained over 800 MPa until reaching the strain of 40 pct. Both tungsten and STS fibers favorably affected the strength and ductility of the composites by interrupting the propagation of shear bands formed in the amorphous matrix, by dispersing the stress applied to the matrix, and by promoting deformation mechanisms such as fiber buckling. These findings confirmed the possibility to apply the continuous-fiber-reinforced amorphous alloy matrix composites to structural materials requiring excellent properties.
A R Chambers - One of the best experts on this subject based on the ideXlab platform.
-
understanding the factors affecting the Compressive Testing of unidirectional carbon fibre composites
Composites Part B-engineering, 2007Co-Authors: Charlene A Squires, Keith H Netting, A R ChambersAbstract:An investigation was conducted to establish the effects of specimen preparation and configuration on the measured Compressive strength of unidirectional carbon fibre. The Compressive strength was determined through ASTM D 695 M [ASTM D 695 M, Standard Test method for Compressive properties of rigid plastics. http://www.astm.org] Test method. Specimens conforming to this standard were produced with different thickness, edge and surface preparation. Optical and electron (SEM) microscopical techniques were used to assess initiation of failure and to quantify the damage encountered by the Compressive Test specimen. The findings correlated well with the mechanical Test results, additionally; from the mechanical Testing there was significant evidence to suggest that the failure mechanism is dependent upon the quality of the preparation of the Test specimen.
-
understanding the factors affecting the Compressive Testing of unidirectional carbon fibre composites
Composites Part B-engineering, 2007Co-Authors: Charlene A Squires, Keith H Netting, A R ChambersAbstract:An investigation was conducted to establish the effects of specimen preparation and configuration on the measured Compressive strength of unidirectional carbon fibre. The Compressive strength was determined through ASTM D 695 M [ASTM D 695 M, Standard Test method for Compressive properties of rigid plastics. http://www.astm.org] Test method. Specimens conforming to this standard were produced with different thickness, edge and surface preparation. Optical and electron (SEM) microscopical techniques were used to assess initiation of failure and to quantify the damage encountered by the Compressive Test specimen. The findings correlated well with the mechanical Test results, additionally; from the mechanical Testing there was significant evidence to suggest that the failure mechanism is dependent upon the quality of the preparation of the Test specimen.
Hyunmin Kim - One of the best experts on this subject based on the ideXlab platform.
-
dynamic tension compression asymmetry of martensitic transformation in austenitic fe 0 4 1 0 c 18mn steels for cryogenic applications
Acta Materialia, 2015Co-Authors: Hyunmin Kim, Nack J. Kim, Jaeyoung Park, Wooyeol Kim, Seok Su Sohn, Hyoung Seop Kim, Byeongjoo Lee, Sunghak LeeAbstract:Abstract In this study, cryogenic-temperature dynamic mechanical properties of austenitic Fe–(0.4, 1.0)C–18Mn steels were evaluated by conducting dynamic tensile and Compressive Tests, and deformation mechanisms including tension–compression asymmetry of martensitic transformation behavior were interpreted by microstructural evolution of dynamically tensioned or compressed specimens. After the dynamic tensile Test of the 0.4C–18Mn steel, the γ → ɛ → α ′ martensitic transformation occurred at −196 °C, whereas ɛ - or α ′-martensite was not found in the 1.0C–18Mn steel. After the dynamic Compressive Test, on the other hand, the γ → ɛ martensitic transformation occurred at −196 °C without the formation of α ′-martensites in the 0.4C–18Mn steel. This dynamic tensile-Compressive asymmetry of martensitic transformation was plausibly interpreted by austenite stability in relation with difference in molar volume, hydrostatic stress distribution, and adiabatic heating. The γ → α ′ transformation was prevented under the dynamic Compressive loading because the increase in molar volume was required for the γ → α ′ transformation, whereas it was promoted to induce the γ → ɛ → α ′ transformation under dynamic tensile loading.
-
interpretation of cryogenic temperature charpy fracture initiation and propagation energies by microstructural evolution occurring during dynamic Compressive Test of austenitic fe 0 4 1 0 c 18mn steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Hyunmin Kim, Jaeyoung Park, Seok Su Sohn, Joong Eun Jung, Sunghak LeeAbstract:In the present study, Charpy impact energy (ET) composed of fracture initiation energy (EI) and propagation energy (EP) of austenitic Fe–(0.4,1.0)C–18Mn steels was evaluated in the temperature range from room to cryogenic temperatures by an instrumented Charpy impact Tester, and was interpreted by microstructural evolution of dynamically compressed specimens. In the 1.0C–18Mn steel, the EI and EP decreased slightly with decreasing temperature, but the EP/ET ratio was kept to be about 0.5. In the 0.4C–18Mn steel, the EI remained almost constant or slightly decreased with decreasing temperature, while the EP/ET ratio steadily decreased, thereby leading to the lower (about 30%) cryogenic-temperature ET than that of the 1.0C–18Mn steel. Under the dynamic Compressive loading, a considerable number of e-martensites were formed in the 0.4C–18Mn steel, whereas they were not found in the 1.0C–18Mn steel, and their volume fractions increased steadily with decreasing temperature. This γ→e-martensite transformation was attributed to the decrease in stacking fault energy, and resulted in the very low EP and resultant ET.
-
effects of dynamic strain hardening exponent on abnormal cleavage fracture occurring during drop weight tear Test of api x70 and x80 linepipe steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2014Co-Authors: Minju Kang, Hyunmin Kim, Sunghak Lee, Sang Yong ShinAbstract:In this study, drop weight tear Tests (DWTT) were conducted on API X70 and X80 linepipe steels fabricated with various compositions and rolling and cooling conditions in order to correlate the strain hardening with the abnormal cleavage fracture occurring in the hammer-impacted area. Area fractions of fracture modes were measured from fractured DWTT specimens, and the measured data were analyzed in relation to microstructures, Charpy impact energy, and strain hardening. All the steels consisted of fine acicular ferrite, together with some bainitic ferrite, granular bainite, and martensite-austenite constituent. As the volume fraction of acicular ferrite increased, the area fraction of DWTT abnormal cleavage fracture decreased because the toughness of acicular ferrite was higher than other microstructures. The area fraction of abnormal cleavage fracture was weakly related with strain hardening exponents obtained from the quasi-static tensile and Compressive Tests, but showed better correlation with those obtained from the dynamic Compressive Test. This tendency could be more clearly observed when steels having similar Charpy impact energy levels were grouped. Since the DWTT was performed under a dynamic loading condition, thus, the abnormal cleavage fracture behavior should be related with the strain hardening analyzed under a dynamic loading condition.
Charlene A Squires - One of the best experts on this subject based on the ideXlab platform.
-
understanding the factors affecting the Compressive Testing of unidirectional carbon fibre composites
Composites Part B-engineering, 2007Co-Authors: Charlene A Squires, Keith H Netting, A R ChambersAbstract:An investigation was conducted to establish the effects of specimen preparation and configuration on the measured Compressive strength of unidirectional carbon fibre. The Compressive strength was determined through ASTM D 695 M [ASTM D 695 M, Standard Test method for Compressive properties of rigid plastics. http://www.astm.org] Test method. Specimens conforming to this standard were produced with different thickness, edge and surface preparation. Optical and electron (SEM) microscopical techniques were used to assess initiation of failure and to quantify the damage encountered by the Compressive Test specimen. The findings correlated well with the mechanical Test results, additionally; from the mechanical Testing there was significant evidence to suggest that the failure mechanism is dependent upon the quality of the preparation of the Test specimen.
-
understanding the factors affecting the Compressive Testing of unidirectional carbon fibre composites
Composites Part B-engineering, 2007Co-Authors: Charlene A Squires, Keith H Netting, A R ChambersAbstract:An investigation was conducted to establish the effects of specimen preparation and configuration on the measured Compressive strength of unidirectional carbon fibre. The Compressive strength was determined through ASTM D 695 M [ASTM D 695 M, Standard Test method for Compressive properties of rigid plastics. http://www.astm.org] Test method. Specimens conforming to this standard were produced with different thickness, edge and surface preparation. Optical and electron (SEM) microscopical techniques were used to assess initiation of failure and to quantify the damage encountered by the Compressive Test specimen. The findings correlated well with the mechanical Test results, additionally; from the mechanical Testing there was significant evidence to suggest that the failure mechanism is dependent upon the quality of the preparation of the Test specimen.
Zhiqiang Yin - One of the best experts on this subject based on the ideXlab platform.
-
dynamic Compressive Test of gas containing coal using a modified split hopkinson pressure bar system
Rock Mechanics and Rock Engineering, 2020Co-Authors: Zhiqiang Yin, Wensu Chen, Hong Hao, Jucai Chang, Guangming Zhao, Zhiyu Chen, Kang PengAbstract:In deep mine, coal is usually subjected to coupled high gas pressure and static Compressive stress. The coal may be also subjected to dynamic loading due to the sudden fracture of hard roof during mining. In our previous study, the behaviour of gas-containing coals with initial gas pressure was investigated subjected to uniaxial static compression. In this study, the dynamic Compressive behaviour of gas-containing coals with gas pressure and static axial preloading is investigated using a modified Split Hopkinson Pressure Bar (SHPB) system. The dynamic behaviours of gas-containing coals under SHPB Tests are studied by varying initial gas pressure and axial static preloading. The Testing results include strain measurements and energy dissipation. In addition, the wave impedance method is used to quantify damage of gas-containing coals under coupled gas-static-dynamic load. It is found that the dynamic Compressive strength of gas-containing coal under coupled load decreases with the increasing initial gas pressure. The gas-containing coal with higher gas pressure and axial static preloading is more vulnerable to dynamic loading. The findings can be applied to mining design or support design in deep mining of high-gas-containing coal seam.