Search2005 Vol. 12, No. 1
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2005, vol. 12, no. 1, pp.
1-5.
Abstract:
A mechanical model is proposed for the system of elastic beam and strain-softening pillar where strain localization is initiated at peak shear stress. To obtain the plastic deformation of the pillar due to the shear slips of multiple shear bands, the pillar is divided into several narrow slices where compressive deformation is treated as uniformity. In the light of the compatibility condition of deformation, the total compressive displacement of the pillar is equal to the displacement of the beam in the middle span. An insta bility criterion is derived analytically based on the energy principle using a known size of localization band according to gradientdependent plasticity. The main advantage of the present model is that the effects of the constitutive parameters of rock and the geometrical size of structure are reflected in the criterion. The condition that the derivative of distributed load with respect to the deflection of the beam in the middle span is less than zero is not only equivalent to, but also even more concise in form than the instability criterion. To study the influences of constitutive parameters and geometrical size on stability, some examples are presented.
A mechanical model is proposed for the system of elastic beam and strain-softening pillar where strain localization is initiated at peak shear stress. To obtain the plastic deformation of the pillar due to the shear slips of multiple shear bands, the pillar is divided into several narrow slices where compressive deformation is treated as uniformity. In the light of the compatibility condition of deformation, the total compressive displacement of the pillar is equal to the displacement of the beam in the middle span. An insta bility criterion is derived analytically based on the energy principle using a known size of localization band according to gradientdependent plasticity. The main advantage of the present model is that the effects of the constitutive parameters of rock and the geometrical size of structure are reflected in the criterion. The condition that the derivative of distributed load with respect to the deflection of the beam in the middle span is less than zero is not only equivalent to, but also even more concise in form than the instability criterion. To study the influences of constitutive parameters and geometrical size on stability, some examples are presented.
2005, vol. 12, no. 1, pp.
6-11.
Abstract:
A prediction method of strata movement in underground metal mines is put forward, in which fuzzy BP neural network is applied. The results show that there is a strong nonlinear relation between the selected factors and strata movement angle, the anticipant and the actual output results are very similar. It is proved that the numerical value of movement angle is correlated with the selected factors in theory. The scope of strata and surface movement due to mining can be predicted. This research provides a thought to study the movement scope of strata due to mining.
A prediction method of strata movement in underground metal mines is put forward, in which fuzzy BP neural network is applied. The results show that there is a strong nonlinear relation between the selected factors and strata movement angle, the anticipant and the actual output results are very similar. It is proved that the numerical value of movement angle is correlated with the selected factors in theory. The scope of strata and surface movement due to mining can be predicted. This research provides a thought to study the movement scope of strata due to mining.
2005, vol. 12, no. 1, pp.
12-15.
Abstract:
The explosivity experiment of anti-explosive ammonium nitrate (AEAN) shows that the explosive characteristic of AEAN is eliminated. The adiabatic decompositions of ammonium nitrate and AEAN were investigated with an accelerating rate calorimeter (ARC). The curves of thermal decomposition temperature and pressure versus time, self-heating rate and pressure versus temperature for two systems were obtained. The kinetic parameters such as apparent activation energy and pre-exponential factor were calculated.The safety of AEAN was analyzed. It was indicated that AEAN has a higher thermal stability than AN. At the same time, it can be shown that the elimination of its explosive characteristic is due to the improvement on the thermal stability of AEAN.
The explosivity experiment of anti-explosive ammonium nitrate (AEAN) shows that the explosive characteristic of AEAN is eliminated. The adiabatic decompositions of ammonium nitrate and AEAN were investigated with an accelerating rate calorimeter (ARC). The curves of thermal decomposition temperature and pressure versus time, self-heating rate and pressure versus temperature for two systems were obtained. The kinetic parameters such as apparent activation energy and pre-exponential factor were calculated.The safety of AEAN was analyzed. It was indicated that AEAN has a higher thermal stability than AN. At the same time, it can be shown that the elimination of its explosive characteristic is due to the improvement on the thermal stability of AEAN.
2005, vol. 12, no. 1, pp.
16-22.
Abstract:
The measurement and control of the molten steel level are studied, which affect the quality of strip surface in strip casting.A system of molten steel measurement with a CCD (Charge Coupled Devices) sensor is designed, real-time measured data are given and its precision is analyzed. The level fluctuation model is derived, and an adaptive fuzzy-PID controller with supervisory control (AFPS) is proposed. The stability of the system is proved using Lyapunov theorem, and the simulation results are given when the model, the casting speed and the roll gap change. It is suggested that this kind of coupled nonlinear and time varying system is stable and robust using the designed AFPS controller.
The measurement and control of the molten steel level are studied, which affect the quality of strip surface in strip casting.A system of molten steel measurement with a CCD (Charge Coupled Devices) sensor is designed, real-time measured data are given and its precision is analyzed. The level fluctuation model is derived, and an adaptive fuzzy-PID controller with supervisory control (AFPS) is proposed. The stability of the system is proved using Lyapunov theorem, and the simulation results are given when the model, the casting speed and the roll gap change. It is suggested that this kind of coupled nonlinear and time varying system is stable and robust using the designed AFPS controller.
2005, vol. 12, no. 1, pp.
23-25.
Abstract:
The dipping experiment was carried out by putting the water-cooled copper plate into the stannum-lead alloy to simulate the process of initial solidification of steel, and the result that the heat transfer of original shell improved by grooving on the surface of the water-cooled copper plate was investigated. A mathematical model of heat transfer was set up and the temperature field of casting slab 1000 mm×200mm was calculated. The experimentation and simulation results indicate that the inside-grooved mould could improve the heat transfer of original shell, decrease the non-uniformity of original shell thickness and reduce the longitudinal surface cracks of casting slab.
The dipping experiment was carried out by putting the water-cooled copper plate into the stannum-lead alloy to simulate the process of initial solidification of steel, and the result that the heat transfer of original shell improved by grooving on the surface of the water-cooled copper plate was investigated. A mathematical model of heat transfer was set up and the temperature field of casting slab 1000 mm×200mm was calculated. The experimentation and simulation results indicate that the inside-grooved mould could improve the heat transfer of original shell, decrease the non-uniformity of original shell thickness and reduce the longitudinal surface cracks of casting slab.
2005, vol. 12, no. 1, pp.
26-32.
Abstract:
The 2-dimensional cellular automata (CA) simulation technique has been utilized to investigate the abnormal grain coarsening. The growth of abnormal grains is modelled under this assumption that different grains have different boundary energies and boundary mobilities. As temperature increases, some grains may first get rid of the particle pinning effect. Thus a high probability is obtained for atoms to jump over the boundary, so that they can consume other primary retained grains quickly. From the simulation,the characteristics of the abnormal grain coarsening under different conditions are demonstrated successfully. An experiment has also been carried out to reflect the abnormal grain coarsening on the microalloy steel. Simulation results are quite close to the experimental evidence.
The 2-dimensional cellular automata (CA) simulation technique has been utilized to investigate the abnormal grain coarsening. The growth of abnormal grains is modelled under this assumption that different grains have different boundary energies and boundary mobilities. As temperature increases, some grains may first get rid of the particle pinning effect. Thus a high probability is obtained for atoms to jump over the boundary, so that they can consume other primary retained grains quickly. From the simulation,the characteristics of the abnormal grain coarsening under different conditions are demonstrated successfully. An experiment has also been carried out to reflect the abnormal grain coarsening on the microalloy steel. Simulation results are quite close to the experimental evidence.
2005, vol. 12, no. 1, pp.
33-37.
Abstract:
Barium titanate powder on nanometer scale was synthesized by means of co-precipitation. The thermal mass loss, crystal grain growth and phase transition of the barium titanate nanometer powder were investigated by TG (Thermogravimetric)-DTA (Differential scanning calorimetric) and XRD (X-ray powder diffractometer) at different heat treatment temperatures. The results show that amorphous barium titanate powder can transfer into tetragonal symmetry structure after heat treatment. When the heat treatment temperature is below 900℃, the grains grow rapidly because the activation energy at low temperature is greatly less than that at high temperature. By controlling theheat treatment temperature, the optimization of the barium titanate crystallite size and formation of tetragonal phase can be realized.
Barium titanate powder on nanometer scale was synthesized by means of co-precipitation. The thermal mass loss, crystal grain growth and phase transition of the barium titanate nanometer powder were investigated by TG (Thermogravimetric)-DTA (Differential scanning calorimetric) and XRD (X-ray powder diffractometer) at different heat treatment temperatures. The results show that amorphous barium titanate powder can transfer into tetragonal symmetry structure after heat treatment. When the heat treatment temperature is below 900℃, the grains grow rapidly because the activation energy at low temperature is greatly less than that at high temperature. By controlling theheat treatment temperature, the optimization of the barium titanate crystallite size and formation of tetragonal phase can be realized.
2005, vol. 12, no. 1, pp.
38-42.
Abstract:
Three approaches of treating carbon nanotubes (CNTs) including acid treatment, air oxidization and heat treatment at high temperature were studied to enhance the crystalline degree of carbon nanotubes. High temperature heat-treatment elevates the crystalline degree of carbon nanotubes. Acid treatment removes parts of amorphous carbonaceous matter through its oxidization effect.Air oxidization disperses carbon nanotubes and amorphous carbonaceous matter. The treatment of combining acid treatment with heat-treatment further elevates the crystalline degree of carbon nanotubes comparing with acid treatment or heat-treatment. The combination of the three treatments creates the thorough effects of enhancing the crystalline degree of carbon nanotubes.
Three approaches of treating carbon nanotubes (CNTs) including acid treatment, air oxidization and heat treatment at high temperature were studied to enhance the crystalline degree of carbon nanotubes. High temperature heat-treatment elevates the crystalline degree of carbon nanotubes. Acid treatment removes parts of amorphous carbonaceous matter through its oxidization effect.Air oxidization disperses carbon nanotubes and amorphous carbonaceous matter. The treatment of combining acid treatment with heat-treatment further elevates the crystalline degree of carbon nanotubes comparing with acid treatment or heat-treatment. The combination of the three treatments creates the thorough effects of enhancing the crystalline degree of carbon nanotubes.
2005, vol. 12, no. 1, pp.
43-47.
Abstract:
The fine structure of M/A islands in pipeline steel X70 has been studied by transmission electron microscope (TEM). It is shown that the M/A islands are about 1-2 μm in size and distribute at the grain boundary of irregular massive ferrite or acicular ferrite in the microstructure of the steel undergoing TMCP (thermo-mechanical controlled processing). The analysis of diffraction contrast shows that the M/A islands consist of retained austenite and some martensite lamellae different in size and orientation. The microtwinning and midrib exist in the lamella of lenticular martensite, which exhibit the typical character of high-carbon martensite. The influences of TMCP parameterson M/A islands have been studied carefully. With the increase of the cooling speed, the amount of M/A islands decrease slightly and the morphology of M/A islands changes to thin dispersive short bars from thick irregular long strips.
The fine structure of M/A islands in pipeline steel X70 has been studied by transmission electron microscope (TEM). It is shown that the M/A islands are about 1-2 μm in size and distribute at the grain boundary of irregular massive ferrite or acicular ferrite in the microstructure of the steel undergoing TMCP (thermo-mechanical controlled processing). The analysis of diffraction contrast shows that the M/A islands consist of retained austenite and some martensite lamellae different in size and orientation. The microtwinning and midrib exist in the lamella of lenticular martensite, which exhibit the typical character of high-carbon martensite. The influences of TMCP parameterson M/A islands have been studied carefully. With the increase of the cooling speed, the amount of M/A islands decrease slightly and the morphology of M/A islands changes to thin dispersive short bars from thick irregular long strips.
2005, vol. 12, no. 1, pp.
48-53.
Abstract:
The deformation behavior and the contact area of conductive particles in anisotropically conductive adhesives (ACA) were investigated by finite element method (FEM). The solid conductive particles are made of pure Ni and Cu. The results indicate that the deformation of the conductive particles is inhomogeneous during fabrication. When the reduction in height is small the deformation concentrates in the area near the contact area. As the reduction in height increases, the strain in the area near the contact area increases, and the metal flows toward the circumference, resulting in the increase of the contact area between the conductive particles and pad. The higher the degree of deformation, the larger the contact area. The regression equations were offered to express the relations between the bounding force and the contact area or the reduction in height. An approach of how to obtain the maximum contact area in ACA was discussed.
The deformation behavior and the contact area of conductive particles in anisotropically conductive adhesives (ACA) were investigated by finite element method (FEM). The solid conductive particles are made of pure Ni and Cu. The results indicate that the deformation of the conductive particles is inhomogeneous during fabrication. When the reduction in height is small the deformation concentrates in the area near the contact area. As the reduction in height increases, the strain in the area near the contact area increases, and the metal flows toward the circumference, resulting in the increase of the contact area between the conductive particles and pad. The higher the degree of deformation, the larger the contact area. The regression equations were offered to express the relations between the bounding force and the contact area or the reduction in height. An approach of how to obtain the maximum contact area in ACA was discussed.
2005, vol. 12, no. 1, pp.
54-59.
Abstract:
The prediction behaviors of some coherent plane wave equations for the effective velocities and attenuations of the coherent plane waves propagating through a composite material and for the effective elastic moduli of the composites are studied. The numerical results obtained by Waterman & Truell's, Twersky's and Gubernatis's equations for Glass-Epoxy composites with various volume fractions are compared. It is found that the predictions by both Twersky's and Gubematis's equations underestimate the effective velocities and the effective elastic moduli when compare with the predictions by Waterman & Truell's equation. Furthermore,the deviations are more evident for the shear wave than that for the longitudinal wave. But these deviations decrease gradually with the increase of the frequency and increase gradually with the increase of the volume fraction.
The prediction behaviors of some coherent plane wave equations for the effective velocities and attenuations of the coherent plane waves propagating through a composite material and for the effective elastic moduli of the composites are studied. The numerical results obtained by Waterman & Truell's, Twersky's and Gubernatis's equations for Glass-Epoxy composites with various volume fractions are compared. It is found that the predictions by both Twersky's and Gubematis's equations underestimate the effective velocities and the effective elastic moduli when compare with the predictions by Waterman & Truell's equation. Furthermore,the deviations are more evident for the shear wave than that for the longitudinal wave. But these deviations decrease gradually with the increase of the frequency and increase gradually with the increase of the volume fraction.
2005, vol. 12, no. 1, pp.
60-66.
Abstract:
The behavior of rolling contact fatigue (RCF) of medium carbon bainitic back-up roll steel was investigated under its actual work conditions. A kind of asperity-scale surface originated cracks, which is lying parallel or at an acute angle to the surfaces, initiated after unidirectional plastic flow of the material in thin surface layer had occurred. Theoretical analysis indicates that they nucleate due to plastic ratcheting induced by asperity contact stresses, and consequently are named as ratcheting cracks. After nucleating and initially propagating, they arrest at some depth and resume propagating till about 70%-80% of the RCF failure life by initially turning parallel to contact surfaces. Their behavior of initiation and propagation is confined to a thin layer prior to the formation of surface distress. According to the critical principle of the preventive grinding strategy, removing the asperity influenced surface layer at about 70%-80% of the RCF failure life can effectively prevent the ratcheting cracks from developing into surface distress, which can lead to the formation of macro-RCF failure soon.
The behavior of rolling contact fatigue (RCF) of medium carbon bainitic back-up roll steel was investigated under its actual work conditions. A kind of asperity-scale surface originated cracks, which is lying parallel or at an acute angle to the surfaces, initiated after unidirectional plastic flow of the material in thin surface layer had occurred. Theoretical analysis indicates that they nucleate due to plastic ratcheting induced by asperity contact stresses, and consequently are named as ratcheting cracks. After nucleating and initially propagating, they arrest at some depth and resume propagating till about 70%-80% of the RCF failure life by initially turning parallel to contact surfaces. Their behavior of initiation and propagation is confined to a thin layer prior to the formation of surface distress. According to the critical principle of the preventive grinding strategy, removing the asperity influenced surface layer at about 70%-80% of the RCF failure life can effectively prevent the ratcheting cracks from developing into surface distress, which can lead to the formation of macro-RCF failure soon.
2005, vol. 12, no. 1, pp.
67-71.
Abstract:
By simulating edge dislocation emissions from a mode I crack tip along multiple inclined slip planes, the plastic zone and dislocation-free zone around the crack tip are obtained. It is found that the shape of the mode I plastic zone consists of two leaning forward loops which is better agreement with experimental observations. Except at the crack tip there are also stress peaks in front of the crack tip. A formula of the maximum peak stress as a function of the applied stress intensity factor and the friction stress has been regressed.
By simulating edge dislocation emissions from a mode I crack tip along multiple inclined slip planes, the plastic zone and dislocation-free zone around the crack tip are obtained. It is found that the shape of the mode I plastic zone consists of two leaning forward loops which is better agreement with experimental observations. Except at the crack tip there are also stress peaks in front of the crack tip. A formula of the maximum peak stress as a function of the applied stress intensity factor and the friction stress has been regressed.
2005, vol. 12, no. 1, pp.
72-77.
Abstract:
To understand the complexity of the mathematical models of a proton exchange membrane fuel cell (PEMFC) and their shortage of practical PEMFC control, the PEMFC complex mechanism and the existing PEMFC models are analyzed, and artificial neural networks based PEMFC modeling is advanced. The structure, algorithm, training and simulation of PEMFC modeling based on improved BP networks are given out in detail. The computer simulation and conducted experiment verify that this model is fast and accurate, and can be used as a suitable operational model for PEMFC real-time control.
To understand the complexity of the mathematical models of a proton exchange membrane fuel cell (PEMFC) and their shortage of practical PEMFC control, the PEMFC complex mechanism and the existing PEMFC models are analyzed, and artificial neural networks based PEMFC modeling is advanced. The structure, algorithm, training and simulation of PEMFC modeling based on improved BP networks are given out in detail. The computer simulation and conducted experiment verify that this model is fast and accurate, and can be used as a suitable operational model for PEMFC real-time control.
2005, vol. 12, no. 1, pp.
78-80.
Abstract:
YSZ (yttria stabilized zirconia) electrolyte properties made from different sizes of nano powders were investigated. As a result, the sample marked KD with the smallest size (10 nm) of first particles and the sample marked TH with narrow distribution and the smallest median diameter Mmed of 0.49 μm have the best sintering properties and the highest electrical conductivity. There is a very well correlation between the density and the electrical conductivity of YSZ, that is, the samples with a higher density have a higher electrical conductivity. The area resistance of YSZ electrolyte made in the experiment, such as TH of 0.483 Ω·cm2, is much lower than that of the sample D of 1.300 Ω·cm2 made in Germany at 850℃. The complex resistance of YSZ electrolyte made in the experiment at the grain, grain boundary and electrode in the range of 300-750℃ decreases greatly compared to the sample made in Germany by shown in the complex impedance plot.
YSZ (yttria stabilized zirconia) electrolyte properties made from different sizes of nano powders were investigated. As a result, the sample marked KD with the smallest size (10 nm) of first particles and the sample marked TH with narrow distribution and the smallest median diameter Mmed of 0.49 μm have the best sintering properties and the highest electrical conductivity. There is a very well correlation between the density and the electrical conductivity of YSZ, that is, the samples with a higher density have a higher electrical conductivity. The area resistance of YSZ electrolyte made in the experiment, such as TH of 0.483 Ω·cm2, is much lower than that of the sample D of 1.300 Ω·cm2 made in Germany at 850℃. The complex resistance of YSZ electrolyte made in the experiment at the grain, grain boundary and electrode in the range of 300-750℃ decreases greatly compared to the sample made in Germany by shown in the complex impedance plot.
2005, vol. 12, no. 1, pp.
81-84.
Abstract:
The EMF (electromotive force) expressions of bielectrolyte solid-state sensors derived from classical thermodynamics are not rigorous. They are only applicable in some special situations. In order to expand their applicable scope, they should be derived from irreversible thermodynamics theory. There is a junction potential term in the EMF equations of double solid electrolyte sensors derived from irreversible thermodynamics. The junction potential involves the ion transference numbers and the electron transference numbers of two kinds of solid electrolytes. When the transference numbers of reaction ions in the two solid electrolytes equal 1 only,the junction potential term is zero and two types of EMF equations become the same.
The EMF (electromotive force) expressions of bielectrolyte solid-state sensors derived from classical thermodynamics are not rigorous. They are only applicable in some special situations. In order to expand their applicable scope, they should be derived from irreversible thermodynamics theory. There is a junction potential term in the EMF equations of double solid electrolyte sensors derived from irreversible thermodynamics. The junction potential involves the ion transference numbers and the electron transference numbers of two kinds of solid electrolytes. When the transference numbers of reaction ions in the two solid electrolytes equal 1 only,the junction potential term is zero and two types of EMF equations become the same.
2005, vol. 12, no. 1, pp.
85-89.
Abstract:
The microhardness of piston rods treated with different induction hardening processes was tested. The experimental results reveal that the depth of the hardened zone is proportional to the ratio of the moving speed of the piston rod to the output power of the induction generator. This result is proved correct through the Finite Element Method (FEM) simulation of the thermal field of induction heating. From tensile and impact tests, an optimized high frequency induction hardening process for piston rods has been obtained, where the output power was 82%×80 kW and the moving speed of workpiece was 5364 mm/min. The piston rods, treated by the optimized high frequency induction hardening process, show the best comprehensive mechanical performance.
The microhardness of piston rods treated with different induction hardening processes was tested. The experimental results reveal that the depth of the hardened zone is proportional to the ratio of the moving speed of the piston rod to the output power of the induction generator. This result is proved correct through the Finite Element Method (FEM) simulation of the thermal field of induction heating. From tensile and impact tests, an optimized high frequency induction hardening process for piston rods has been obtained, where the output power was 82%×80 kW and the moving speed of workpiece was 5364 mm/min. The piston rods, treated by the optimized high frequency induction hardening process, show the best comprehensive mechanical performance.
Theoretical modeling of cutting temperature in high-speed end milling process for die/mold machining
2005, vol. 12, no. 1, pp.
90-95.
Abstract:
A parametric model of cutting temperature generated in end milling process is developed according to the thermal mechanism of end milling as an intermittent operation, which periodically repeats the cycle of heating under cutting and cooling under noncutting. It shows that cutting speed and the tool-workpiece engagement condition are determinative for tool temperature in the operation. The suggested model was investigated by tests of AlTiN coated endmill machining hardened die steel JIS SKD61, where cutting temperature on the flank face of tool was measured with an optical fiber type radiation thermometer. Experimental results show that the tendency of cutting temperature to increase with cutting speed and engagement angle is intensified with the progressing tool wear.
A parametric model of cutting temperature generated in end milling process is developed according to the thermal mechanism of end milling as an intermittent operation, which periodically repeats the cycle of heating under cutting and cooling under noncutting. It shows that cutting speed and the tool-workpiece engagement condition are determinative for tool temperature in the operation. The suggested model was investigated by tests of AlTiN coated endmill machining hardened die steel JIS SKD61, where cutting temperature on the flank face of tool was measured with an optical fiber type radiation thermometer. Experimental results show that the tendency of cutting temperature to increase with cutting speed and engagement angle is intensified with the progressing tool wear.
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