Transactions of Nanjing University of Aeronautics & Astronautics
Volume 37,Issue 3,2020 Table of Contents
2020, 37(3):353-359.
DOI: 10.16356/j.1005-1120.2020.03.001
Abstract:
The aramid fiber-reinforced composites (AFRC) can increase the durability of corresponding applications such as aerospace, automobile and other large structural parts, due to the improvement in hardness, heat build-up, wear properties and green environmental protection. However, because of its complex multiphase structure and unique heterogeneity and anisotropy, the poor compression fatigue resistance and the incident surface fibrillation are inevitable. To improve the assembly precision of AFRC, mechanical processing is necessary to meet the dimensional accuracy. This paper focuses on the influence of contour milling parameters on delamination defects during milling of AFRC laminates. A series of milling experiments are conducted and two different kinds of delamination defects including tearing delamination and uncut-off delamination are investigated. A computing method and model based on brittle fracture for the two different types of delamination are established. The results can be used for explaining the mechanism and regularity of delamination defects. The control strategy of delamination defects and evaluation method of finished surface integrity are further discussed. The results are meaningful to optimize cutting parameters, and provide a clear understanding of surface defects control.
The aramid fiber-reinforced composites (AFRC) can increase the durability of corresponding applications such as aerospace, automobile and other large structural parts, due to the improvement in hardness, heat build-up, wear properties and green environmental protection. However, because of its complex multiphase structure and unique heterogeneity and anisotropy, the poor compression fatigue resistance and the incident surface fibrillation are inevitable. To improve the assembly precision of AFRC, mechanical processing is necessary to meet the dimensional accuracy. This paper focuses on the influence of contour milling parameters on delamination defects during milling of AFRC laminates. A series of milling experiments are conducted and two different kinds of delamination defects including tearing delamination and uncut-off delamination are investigated. A computing method and model based on brittle fracture for the two different types of delamination are established. The results can be used for explaining the mechanism and regularity of delamination defects. The control strategy of delamination defects and evaluation method of finished surface integrity are further discussed. The results are meaningful to optimize cutting parameters, and provide a clear understanding of surface defects control.
2020, 37(3):360-369.
DOI: 10.16356/j.1005-1120.2020.03.002
Abstract:
A novel polysaccharide-bonded abrasive tool is proposed for the green machining of single-crystal sapphires. The prescription and manufacturing process of the proposed tool is designed, and the gelation property of polysaccharide by microwave treatment is investigated. Abrasive tool samples are fabricated, and a machining experiment on a single-crystal sapphire is performed. It is found that the crystallinity of polysaccharide gel decreases as the proportion of cross-linked polysaccharide increases. Abrasive tool samples with cross-linked polysaccharide present higher surface hardness. With the new abrasive tool, the surface quality of sapphire wafer can be significantly improved. This new tool with an abrasive to binder ratio of 2∶1 attains a material removal rate of 0.68 μm/min. It is found that increasing the abrasive to binder ratio leads to better self-dressing performance but worse material removal ability and greater loss of abrasive tool materials. The validity of polysaccharide as an abrasive tool binder is preliminarily verified.
A novel polysaccharide-bonded abrasive tool is proposed for the green machining of single-crystal sapphires. The prescription and manufacturing process of the proposed tool is designed, and the gelation property of polysaccharide by microwave treatment is investigated. Abrasive tool samples are fabricated, and a machining experiment on a single-crystal sapphire is performed. It is found that the crystallinity of polysaccharide gel decreases as the proportion of cross-linked polysaccharide increases. Abrasive tool samples with cross-linked polysaccharide present higher surface hardness. With the new abrasive tool, the surface quality of sapphire wafer can be significantly improved. This new tool with an abrasive to binder ratio of 2∶1 attains a material removal rate of 0.68 μm/min. It is found that increasing the abrasive to binder ratio leads to better self-dressing performance but worse material removal ability and greater loss of abrasive tool materials. The validity of polysaccharide as an abrasive tool binder is preliminarily verified.
2020, 37(3):370-376.
DOI: 10.16356/j.1005-1120.2020.03.003
Abstract:
An increase in public environmental awareness and pressures from the government’?s determination to deal with environmental problems force manufacturers to implement green manufacturing (GM). However, since managers and stakeholders lack understanding of GM and its complexity, the manufacturing enterprise, especially the small and medium ones, are constantly facing the problems of how to make a reasonable decision for an environmental problem, and the adopted approaches have no clear payoffs. The customized design, flexible production, and diversified services in customized production make the problems more challenging. In order to solve this problem, this paper proposes a framework for the implementation of GM in customized products manufacturing enterprises (CPME). A three-layer framework, i.e., the goal layer, the product life-cycle layer and the supporting layer, is designed to provide a methodology to help implement GM. In this model, the GM practice processes are divided into four stages from the life-cycle perspective, i.e. design, production, use, and disposal. The preliminary practice of GM in an electrical product manufacturing company is carried out, and the implementation effect shows that the system framework is helpful to make a comprehensive understanding of GM and to improve the operability of GM practices. The integrated product model is an effective way to integrate the life cycle data.
An increase in public environmental awareness and pressures from the government’?s determination to deal with environmental problems force manufacturers to implement green manufacturing (GM). However, since managers and stakeholders lack understanding of GM and its complexity, the manufacturing enterprise, especially the small and medium ones, are constantly facing the problems of how to make a reasonable decision for an environmental problem, and the adopted approaches have no clear payoffs. The customized design, flexible production, and diversified services in customized production make the problems more challenging. In order to solve this problem, this paper proposes a framework for the implementation of GM in customized products manufacturing enterprises (CPME). A three-layer framework, i.e., the goal layer, the product life-cycle layer and the supporting layer, is designed to provide a methodology to help implement GM. In this model, the GM practice processes are divided into four stages from the life-cycle perspective, i.e. design, production, use, and disposal. The preliminary practice of GM in an electrical product manufacturing company is carried out, and the implementation effect shows that the system framework is helpful to make a comprehensive understanding of GM and to improve the operability of GM practices. The integrated product model is an effective way to integrate the life cycle data.
2020, 37(3):377-384.
DOI: 10.16356/j.1005-1120.2020.03.004
Abstract:
Using the devices of split Hopkinson tension bar (SHTB) and split Hopkinson pressure bar (SHPB), the dynamic tension and compression experiments in three typical forming directions (rolling direction （RD）, transverse direction （TD） and normal direction （ND）) were carried out at strain rates of 1 000, 2 000 and 4 000 s-1, respectively. From the microscopic point of view, the effect of strain rate and anisotropy on tension compression asymmetry of aviation aluminum alloy 7050 was studied by scanning electron microscope (SEM), metallographic microscope and electron backscatter diffraction (EBSD). The results showed that there was obvious asymmetry between tension and compression, especially that the yield strength of the material in tension was higher than that in compression. The asymmetry in the elastic stage of tension-compression was weaker and the asymmetry in the strengthening stage was stronger with the increase of strain rate. At the same strain rate, the changing trend of the flow stress was distinct under different orientations of tension and compression, which was related to the stress direction of the grains. According to EBSD grain orientation analysis and raw material texture pole figure analysis, it was found that the larger the difference in the degree of grain refinement during tension and compression, the larger the macro-flow stress difference.
Using the devices of split Hopkinson tension bar (SHTB) and split Hopkinson pressure bar (SHPB), the dynamic tension and compression experiments in three typical forming directions (rolling direction （RD）, transverse direction （TD） and normal direction （ND）) were carried out at strain rates of 1 000, 2 000 and 4 000 s-1, respectively. From the microscopic point of view, the effect of strain rate and anisotropy on tension compression asymmetry of aviation aluminum alloy 7050 was studied by scanning electron microscope (SEM), metallographic microscope and electron backscatter diffraction (EBSD). The results showed that there was obvious asymmetry between tension and compression, especially that the yield strength of the material in tension was higher than that in compression. The asymmetry in the elastic stage of tension-compression was weaker and the asymmetry in the strengthening stage was stronger with the increase of strain rate. At the same strain rate, the changing trend of the flow stress was distinct under different orientations of tension and compression, which was related to the stress direction of the grains. According to EBSD grain orientation analysis and raw material texture pole figure analysis, it was found that the larger the difference in the degree of grain refinement during tension and compression, the larger the macro-flow stress difference.
2020, 37(3):385-392.
DOI: 10.16356/j.1005-1120.2020.03.005
Abstract:
A prediction model for net cutting specific energy in computer numerical control(CNC) turning based on turning parameters and tool wear is developed. The model can predict the net cutting energy consumption before turning. The prediction accuracy of the model is verified in AISI 1045 steel turning. The comparative experimental results show that the prediction accuracy of the model is significantly improved because the influence of tool wear is taken into account. Finally, the influences of turning parameters and tool wear on net cutting specific energy are studied. With the increase of cutting depth, the net cutting specific energy decreases. With the increase of spindle speed, the additional load loss power of spindle drive system increases, so the net cutting specific energy increases. The net cutting specific energy increases approximately linearly with tool wear. The results are helpful to formulate efficient and energy-saving CNC turning schemes and realize low-carbon manufacturing.
A prediction model for net cutting specific energy in computer numerical control(CNC) turning based on turning parameters and tool wear is developed. The model can predict the net cutting energy consumption before turning. The prediction accuracy of the model is verified in AISI 1045 steel turning. The comparative experimental results show that the prediction accuracy of the model is significantly improved because the influence of tool wear is taken into account. Finally, the influences of turning parameters and tool wear on net cutting specific energy are studied. With the increase of cutting depth, the net cutting specific energy decreases. With the increase of spindle speed, the additional load loss power of spindle drive system increases, so the net cutting specific energy increases. The net cutting specific energy increases approximately linearly with tool wear. The results are helpful to formulate efficient and energy-saving CNC turning schemes and realize low-carbon manufacturing.
2020, 37(3):393-402.
DOI: 10.16356/j.1005-1120.2020.03.006
Abstract:
Design of a giant magnetostrictive ultrasonic transducer for progressive sheet forming was presented. A dynamic analysis of the theoretically designed ultrasonic vibration system was carried out using the finite element method(FEM). In addition, simulations were performed to verify the theoretical design. Then, a magnetically conductive material was added between the giant magnetostrictive rod and the permanent magnet. Besides, magnetic field simulations of the transducer were performed. The influence of the material thickness of the magnetically conductive material on uniformity of the induced magnetic field was studied. Furthermore, the impedance analysis and amplitude measurement were performed to compare the performance of transducers with and without the magnetically conductive material. The experimental results show that the magnetic field uniformity is the highest when the magnetically conductive material has a thickness of about 1.6 mm. The output amplitude of the giant magnetostrictive transducer is improved by adding the magnetically conductive material. Moreover, the mechanical quality factor and impedance are reduced, while the transducer operates more stably.
Design of a giant magnetostrictive ultrasonic transducer for progressive sheet forming was presented. A dynamic analysis of the theoretically designed ultrasonic vibration system was carried out using the finite element method(FEM). In addition, simulations were performed to verify the theoretical design. Then, a magnetically conductive material was added between the giant magnetostrictive rod and the permanent magnet. Besides, magnetic field simulations of the transducer were performed. The influence of the material thickness of the magnetically conductive material on uniformity of the induced magnetic field was studied. Furthermore, the impedance analysis and amplitude measurement were performed to compare the performance of transducers with and without the magnetically conductive material. The experimental results show that the magnetic field uniformity is the highest when the magnetically conductive material has a thickness of about 1.6 mm. The output amplitude of the giant magnetostrictive transducer is improved by adding the magnetically conductive material. Moreover, the mechanical quality factor and impedance are reduced, while the transducer operates more stably.
2020, 37(3):403-415.
DOI: 10.16356/j.1005-1120.2020.03.007
Abstract:
The application of cutting fluid is significantly increased in the machining sector to improve productivity. However, the inherent characteristics of cutting fluids on ecology, environment, and society shift the interest of researchers to work on environmentally friendly cooling conditions such as cryogenic cooling. Here, the effect of cutting speed and feed rate on the machining performance of the AISI-L6 tool steel is investigated under cryogenic cooling conditions. Then, the L9 Taguchi based grey relational analysis (GRA) is conducted to investigate the essential machining indices such as cutting energy, surface roughness, tool wear, and material removal rate (MRR). The results indicate that the cutting speed of 160 m/min and feed rate of 0.16 mm/r are the optimum parameters that significantly improves the machining performance of AISI-L6 tool steel.
The application of cutting fluid is significantly increased in the machining sector to improve productivity. However, the inherent characteristics of cutting fluids on ecology, environment, and society shift the interest of researchers to work on environmentally friendly cooling conditions such as cryogenic cooling. Here, the effect of cutting speed and feed rate on the machining performance of the AISI-L6 tool steel is investigated under cryogenic cooling conditions. Then, the L9 Taguchi based grey relational analysis (GRA) is conducted to investigate the essential machining indices such as cutting energy, surface roughness, tool wear, and material removal rate (MRR). The results indicate that the cutting speed of 160 m/min and feed rate of 0.16 mm/r are the optimum parameters that significantly improves the machining performance of AISI-L6 tool steel.
2020, 37(3):416-423.
DOI: 10.16356/j.1005-1120.2020.03.008
Abstract:
A facile method to fabricate wettability pattern (two extreme wettabilities arranged in a pattern) to realize water self-pumping is proposed on cemented carbide while not necessarily depositing other materials on substrate surface. The water self-pumping is achieved by arranging wedge shaped superhydrophilic domain in superhydrophobic substrate using laser machining. Through single factor experiments, it is found that the key to the extreme wettabilities, micro- and nano-structures, is rendered by laser machining processes and is influenced by laser parameters. Meanwhile, the proper laser parameters that are used to fabricate required micro- and nano-structures are obtained. Finally, the water transport experiment is carried out, which shows that the velocity of water bulge could be up to 362 mm/s when the wedge angle is 3°. The mechanism of the water self-pumping is analyzed and it is found that the migration of water bulge is governed by Laplace pressure of the water bulge induced by the wedge micro-groove.
A facile method to fabricate wettability pattern (two extreme wettabilities arranged in a pattern) to realize water self-pumping is proposed on cemented carbide while not necessarily depositing other materials on substrate surface. The water self-pumping is achieved by arranging wedge shaped superhydrophilic domain in superhydrophobic substrate using laser machining. Through single factor experiments, it is found that the key to the extreme wettabilities, micro- and nano-structures, is rendered by laser machining processes and is influenced by laser parameters. Meanwhile, the proper laser parameters that are used to fabricate required micro- and nano-structures are obtained. Finally, the water transport experiment is carried out, which shows that the velocity of water bulge could be up to 362 mm/s when the wedge angle is 3°. The mechanism of the water self-pumping is analyzed and it is found that the migration of water bulge is governed by Laplace pressure of the water bulge induced by the wedge micro-groove.
2020, 37(3):424-433.
DOI: 10.16356/j.1005-1120.2020.03.009
Abstract:
Carbon fiber reinforced silicon carbide matrix (Cf/SiC) composites have the most potential application for high-temperature components of aerospace high-end equipment. However, high cutting temperature, rapid tool wear and severe surface damages are the main problems in dry cutting Cf/SiC composites process. The feasibility study on cryogenic milling of Cf/SiC composites using liquid nitrogen as coolant is investigated. Influences of milling parameters and coolant on temperature, cutting force, surface quality and tool wear are investigated, which is compared with dry cutting. Experimental results reveal that the cutting temperature in cryogenic milling of Cf/SiC composites is reduced by about 40%—60% compared with dry cutting. The milling force increases gradually with the increase of spindle speed, feed rate, depth and width of milling in cryogenic milling process. In addition, the machined surface quality in cryogenic milling is superior to that in dry cutting process. Fiber fracture, matrix damage and fiber matrix debonding are main material removal mechanisms. Flank face wear is the main wear form of the polycrystalline diamond(PCD) end mills. The tool life is prolonged in the cryogenic milling process because the reduced temperature inhibits the softening of Co binder and phase transition of diamond in the PCD end mills.
Carbon fiber reinforced silicon carbide matrix (Cf/SiC) composites have the most potential application for high-temperature components of aerospace high-end equipment. However, high cutting temperature, rapid tool wear and severe surface damages are the main problems in dry cutting Cf/SiC composites process. The feasibility study on cryogenic milling of Cf/SiC composites using liquid nitrogen as coolant is investigated. Influences of milling parameters and coolant on temperature, cutting force, surface quality and tool wear are investigated, which is compared with dry cutting. Experimental results reveal that the cutting temperature in cryogenic milling of Cf/SiC composites is reduced by about 40%—60% compared with dry cutting. The milling force increases gradually with the increase of spindle speed, feed rate, depth and width of milling in cryogenic milling process. In addition, the machined surface quality in cryogenic milling is superior to that in dry cutting process. Fiber fracture, matrix damage and fiber matrix debonding are main material removal mechanisms. Flank face wear is the main wear form of the polycrystalline diamond(PCD) end mills. The tool life is prolonged in the cryogenic milling process because the reduced temperature inhibits the softening of Co binder and phase transition of diamond in the PCD end mills.
2020, 37(3):434-445.
DOI: 10.16356/j.1005-1120.2020.03.010
Abstract:
Chip shape is one of the important factors that affect the processing quality of the deep hole. The flow field of 17 mm standard gun-drill is simulated by taking the coolant pressure as a single factor variable, and the influence of coolant pressure on chip forming is discussed by combining with experiments in this paper. The results show that at the initial stage of chip forming, the flow of cutting fluid will intensify the lateral crimp of chips, and then affect the crimp radius of the chip and the number of turns of the crimp screw. The lateral crimp degree increases first and then decreases with the increase of coolant pressure, and the crimp degree is the smallest at 3 MPa. In addition, during the chip removal process, the stream shrinking in the flow field is the main influencing factor that drive and force the chip to break again, and their influence on the chip removal and chip breaking is proportional to the coolant pressure.
Chip shape is one of the important factors that affect the processing quality of the deep hole. The flow field of 17 mm standard gun-drill is simulated by taking the coolant pressure as a single factor variable, and the influence of coolant pressure on chip forming is discussed by combining with experiments in this paper. The results show that at the initial stage of chip forming, the flow of cutting fluid will intensify the lateral crimp of chips, and then affect the crimp radius of the chip and the number of turns of the crimp screw. The lateral crimp degree increases first and then decreases with the increase of coolant pressure, and the crimp degree is the smallest at 3 MPa. In addition, during the chip removal process, the stream shrinking in the flow field is the main influencing factor that drive and force the chip to break again, and their influence on the chip removal and chip breaking is proportional to the coolant pressure.
2020, 37(3):446-459.
DOI: 10.16356/j.1005-1120.2020.03.011
Abstract:
The methods for reducing interface aperture inconsistency are studied in NC orbital milling (NCOM) of CFRP/Ti6Al4V laminates with coarse pitch. Comparative experiments show burr, aperture inconsistency and error are typical interface defects. Meanwhile, aperture inconsistency and error are more serious than burr in NCOM with coarse pitch. As one of the major causes of interface defects, axial force and radial force are intensively studied. Based upon the machining principle of orbital milling (OM) and the actual hole-making condition in laminated structures, NCOM experiments with coarse pitch are conducted on CFRP/Ti6Al4V laminates under different cutting conditions. Then, the effects of interlayer clamping, minimal quantity lubrication (MQL), twice milling instead of reaming, and interlayer speed change on interface aperture are analyzed. Research shows that interlayer clamping, interlayer speed change and MQL can effectively reduce out-of-tolerance of interface aperture. When making holes of different diameters with one cutter, axial feed has a greater effect on interface aperture precision than tangential feed. When making holes of the same diameter with different cutters, small diameter cutter will reduce interface aperture precision in a single processing. But the method of “twice milling instead of reaming” can improve the aperture precision effectively.
The methods for reducing interface aperture inconsistency are studied in NC orbital milling (NCOM) of CFRP/Ti6Al4V laminates with coarse pitch. Comparative experiments show burr, aperture inconsistency and error are typical interface defects. Meanwhile, aperture inconsistency and error are more serious than burr in NCOM with coarse pitch. As one of the major causes of interface defects, axial force and radial force are intensively studied. Based upon the machining principle of orbital milling (OM) and the actual hole-making condition in laminated structures, NCOM experiments with coarse pitch are conducted on CFRP/Ti6Al4V laminates under different cutting conditions. Then, the effects of interlayer clamping, minimal quantity lubrication (MQL), twice milling instead of reaming, and interlayer speed change on interface aperture are analyzed. Research shows that interlayer clamping, interlayer speed change and MQL can effectively reduce out-of-tolerance of interface aperture. When making holes of different diameters with one cutter, axial feed has a greater effect on interface aperture precision than tangential feed. When making holes of the same diameter with different cutters, small diameter cutter will reduce interface aperture precision in a single processing. But the method of “twice milling instead of reaming” can improve the aperture precision effectively.
XIN Benli
,
SUN Yihang
,
JIA Xiujie
,
LI Fangyi
,
WANG Xing
,
XIONG Sheng
,
MA Mingliang
,
ZHANG Baocai
2020, 37(3):460-466.
DOI: 10.16356/j.1005-1120.2020.03.012
Abstract:
During molten salt cleaning of remanufactured 27SiMn hydraulic support column, oxidation occurs on the surface of metal substrate. This results in a change of the surface roughness of metal substrate after cleaning, which affects subsequent remanufacturing process. To decrease the effect is very important. This paper analyzed the oxidation mechanism of molten salt cleaning, explored the oxidation reaction that occurred during cleaning, and determined the key process parameters of cleaning that affecting oxidation reaction. By using central composite experimental design method and taking surface roughness variation of 27SiMn steel samples before and after molten salt cleaning as response variable to optimize the key process parameters, the optimal parameters of molten salt for cleaning remanufactured 27SiMn hydraulic support column could be obtained. The results show that the oxidation reaction of cleaning paint dirt can protect metal substrate from oxidation to a certain extent, and cleaning temperature and placement depth of metal substrate have a direct impact on the degree of oxidation reaction. When the cleaning temperature is 300 ℃ and the distance between paint dirt and free surface of molten salt is 0.5 times the height of the parts, the surface roughness variation is minimal. Therefore, the cleaning quality will be improved under such parameters.
During molten salt cleaning of remanufactured 27SiMn hydraulic support column, oxidation occurs on the surface of metal substrate. This results in a change of the surface roughness of metal substrate after cleaning, which affects subsequent remanufacturing process. To decrease the effect is very important. This paper analyzed the oxidation mechanism of molten salt cleaning, explored the oxidation reaction that occurred during cleaning, and determined the key process parameters of cleaning that affecting oxidation reaction. By using central composite experimental design method and taking surface roughness variation of 27SiMn steel samples before and after molten salt cleaning as response variable to optimize the key process parameters, the optimal parameters of molten salt for cleaning remanufactured 27SiMn hydraulic support column could be obtained. The results show that the oxidation reaction of cleaning paint dirt can protect metal substrate from oxidation to a certain extent, and cleaning temperature and placement depth of metal substrate have a direct impact on the degree of oxidation reaction. When the cleaning temperature is 300 ℃ and the distance between paint dirt and free surface of molten salt is 0.5 times the height of the parts, the surface roughness variation is minimal. Therefore, the cleaning quality will be improved under such parameters.
2020, 37(3):467-480.
DOI: 10.16356/j.1005-1120.2020.03.013
Abstract:
This paper studied the preparation and mechanical properties of glass fiber reinforced polymer-matrix composite rings prepared by filament winding assisted by ultraviolet (UV) curing. A ray-tracing method was used to calculate the penetration ability of UV light in the resin casting, and then a typical composite ring with dual-curing characteristics was prepared by UV-assisted curing. The effects of winding speed and thermal initiator concentration on the distribution of fiber fraction and mechanical properties were studied. Microscopic morphology was used for the observation of the differences in fiber volume fraction. Mechanical properties tests and scanning electron micrographs were performed to investigate the failure and damage mechanisms of the composite ring samples. The ray tracing results indicate that the UV light can pass through a single yarn thickness and the energy transmitted is sufficient to cure the back side quickly. The experimental results show that the mechanical properties of the composite ring prepared in this paper are comparable to those of the heat-cured samples, which is sufficient to meet the requirements of the flywheel.
This paper studied the preparation and mechanical properties of glass fiber reinforced polymer-matrix composite rings prepared by filament winding assisted by ultraviolet (UV) curing. A ray-tracing method was used to calculate the penetration ability of UV light in the resin casting, and then a typical composite ring with dual-curing characteristics was prepared by UV-assisted curing. The effects of winding speed and thermal initiator concentration on the distribution of fiber fraction and mechanical properties were studied. Microscopic morphology was used for the observation of the differences in fiber volume fraction. Mechanical properties tests and scanning electron micrographs were performed to investigate the failure and damage mechanisms of the composite ring samples. The ray tracing results indicate that the UV light can pass through a single yarn thickness and the energy transmitted is sufficient to cure the back side quickly. The experimental results show that the mechanical properties of the composite ring prepared in this paper are comparable to those of the heat-cured samples, which is sufficient to meet the requirements of the flywheel.
2020, 37(3):481-489.
DOI: 10.16356/j.1005-1120.2020.03.014
Abstract:
Al-FeCoNiCrAl high entropy alloy (HEA) composite coatings were prepared on Ti-6Al-4V via high-energy mechanical alloying (MA). The microstructures and phase composition of the coatings were studied. A continuous and dense coating could be fabricated at a ratio of 35% (weight fraction) Al-FeCoNiCrAl after 4 h milling. The results showed that the thickness of the composite coatings increased first and then decreased with the increase of milling time. And the hardness of coating increased with the increase of milling time. The phase changed during the annealing process. Part of the initial body-centered cubic (BCC) phase of the composite coatings changed into the L12 phase, (Ni, Co)3Al4 and σ phase after annealing above 550 ℃. Ordered BCC was found in the coatings after annealing above 750 ℃. Only BCC and ordered BCC appeared in coatings after annealing above 1 050 ℃. The hardness of the coatings after annealing at 550 ℃ and 750 ℃ was higher than before because of spinodal decomposition and high hardness σ phase. The hardness of the coatings after annealing at 1 050 ℃ decreased because residual stress released.
Al-FeCoNiCrAl high entropy alloy (HEA) composite coatings were prepared on Ti-6Al-4V via high-energy mechanical alloying (MA). The microstructures and phase composition of the coatings were studied. A continuous and dense coating could be fabricated at a ratio of 35% (weight fraction) Al-FeCoNiCrAl after 4 h milling. The results showed that the thickness of the composite coatings increased first and then decreased with the increase of milling time. And the hardness of coating increased with the increase of milling time. The phase changed during the annealing process. Part of the initial body-centered cubic (BCC) phase of the composite coatings changed into the L12 phase, (Ni, Co)3Al4 and σ phase after annealing above 550 ℃. Ordered BCC was found in the coatings after annealing above 750 ℃. Only BCC and ordered BCC appeared in coatings after annealing above 1 050 ℃. The hardness of the coatings after annealing at 550 ℃ and 750 ℃ was higher than before because of spinodal decomposition and high hardness σ phase. The hardness of the coatings after annealing at 1 050 ℃ decreased because residual stress released.
2020, 37(3):490-500.
DOI: 10.16356/j.1005-1120.2020.03.015
Abstract:
This paper intends to develop finite element models that can simulate vehicle load moving on pavement system and reflect the pavement response of vehicle and pavement interaction. We conduct parametric analysis considering the influences of asphalt concrete layer modulus and thickness, base layer modulus and thickness, and subgrade modulus on pavement surface displacement, frequency, and strain response. The analysis findings are fruitful. Both the displacement basin width and maximum value of dynamic surface displacements are larger than those of static surface displacements. The frequency is positively correlated with the pavement structure moduli, and negatively correlated with the pavement structure thicknesses. The shape of dynamic and static tensile strain is similar along the depth of the pavement structure. The maximum value of dynamic tensile strain is larger than that of static tensile strain. The frequency of entire pavement structure holds more significant influence than the surface displacement and strain do. The subgrade modulus has a significant effect on surface displacement, frequency and strain.
This paper intends to develop finite element models that can simulate vehicle load moving on pavement system and reflect the pavement response of vehicle and pavement interaction. We conduct parametric analysis considering the influences of asphalt concrete layer modulus and thickness, base layer modulus and thickness, and subgrade modulus on pavement surface displacement, frequency, and strain response. The analysis findings are fruitful. Both the displacement basin width and maximum value of dynamic surface displacements are larger than those of static surface displacements. The frequency is positively correlated with the pavement structure moduli, and negatively correlated with the pavement structure thicknesses. The shape of dynamic and static tensile strain is similar along the depth of the pavement structure. The maximum value of dynamic tensile strain is larger than that of static tensile strain. The frequency of entire pavement structure holds more significant influence than the surface displacement and strain do. The subgrade modulus has a significant effect on surface displacement, frequency and strain.
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