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Chinese Society of Aeronautics and Astronautics
AECC Beijing Instistute of Aeronautical Materials
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000152
Abstract:
To effectively improve the interlaminar toughness of carbon fiber/epoxy resin (CF/EP) composite laminates, toughening nanoparticles (GO@FeOOH) were prepared by electrostatic self-assembly technology, which was the needle-like hydroxy iron oxide coated with graphene oxide. Dispersed in EP matrix and induced by magnetic field, the toughening effect of GO@FeOOH nanoparticles was significantly improved. The mode I interlaminar toughness (GIC) of GO@FeOOH/CF/EP laminates was examined by double cantilever beam test. The effects of GO@FeOOH and magnetic field induction on GIC were investigated. The results show that the GO@FeOOH can significantly enhance the interlaminar properties of CF/EP composite even at a low content of 0.5wt%, and the initial crack GIC (0.53 kJ·m-2) and crack propagation GIC (0.71 kJ·m-2) of GO@FeOOH/CF/EP are 34.2% and 44.9% higher than those of CF/EP, respectively. On the other hand, the magnetic field induced GO@FeOOH orientation along the magnetic field direction, further significantly improved the toughening effect, the initial crack GIC and crack propagation GIC increased 112.6% and 93.9% compared with CF/EP, respectively. The interlaminar toughening mechanism of the composite mainly includes the pull-out and debonding of the nanoparticles and the local plastic deformation of the matrix, and the pull-out of particles becomes the dominant toughening mechanism after the induction of magnetic field.
To effectively improve the interlaminar toughness of carbon fiber/epoxy resin (CF/EP) composite laminates, toughening nanoparticles (GO@FeOOH) were prepared by electrostatic self-assembly technology, which was the needle-like hydroxy iron oxide coated with graphene oxide. Dispersed in EP matrix and induced by magnetic field, the toughening effect of GO@FeOOH nanoparticles was significantly improved. The mode I interlaminar toughness (GIC) of GO@FeOOH/CF/EP laminates was examined by double cantilever beam test. The effects of GO@FeOOH and magnetic field induction on GIC were investigated. The results show that the GO@FeOOH can significantly enhance the interlaminar properties of CF/EP composite even at a low content of 0.5wt%, and the initial crack GIC (0.53 kJ·m-2) and crack propagation GIC (0.71 kJ·m-2) of GO@FeOOH/CF/EP are 34.2% and 44.9% higher than those of CF/EP, respectively. On the other hand, the magnetic field induced GO@FeOOH orientation along the magnetic field direction, further significantly improved the toughening effect, the initial crack GIC and crack propagation GIC increased 112.6% and 93.9% compared with CF/EP, respectively. The interlaminar toughening mechanism of the composite mainly includes the pull-out and debonding of the nanoparticles and the local plastic deformation of the matrix, and the pull-out of particles becomes the dominant toughening mechanism after the induction of magnetic field.
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000191
Abstract:
The effects of pre-rolling and pre-stretching deformation on microstructure, mechanical properties and corrosion behavior of Al-Cu-Li alloy in subsequent peak-aging were investigated by means of microstructure observation with mechanical and intergranular properties tests. The test results show that the pre-deformation treatment before aging promotes the precipitation of a large number of uniform and fine T1 phase with dispersed distribution in the alloy grain, and reduces the number of precipitates on the grain boundary, so as to improve the comprehensive mechanical properties of the alloy. In addition, this precipitate microstructure can balance the potential difference between the grain boundary and the grain interior, reduce the intergranular corrosion sensitivity of the alloy, reduce the corrosion rate and enhance the intergranular corrosion resistance of the alloy.
The effects of pre-rolling and pre-stretching deformation on microstructure, mechanical properties and corrosion behavior of Al-Cu-Li alloy in subsequent peak-aging were investigated by means of microstructure observation with mechanical and intergranular properties tests. The test results show that the pre-deformation treatment before aging promotes the precipitation of a large number of uniform and fine T1 phase with dispersed distribution in the alloy grain, and reduces the number of precipitates on the grain boundary, so as to improve the comprehensive mechanical properties of the alloy. In addition, this precipitate microstructure can balance the potential difference between the grain boundary and the grain interior, reduce the intergranular corrosion sensitivity of the alloy, reduce the corrosion rate and enhance the intergranular corrosion resistance of the alloy.
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000199
Abstract:
Two-dimensional braided rope is widely used in engineering, aerospace and many other fields, among which 12-strand two-dimensional PBO braided rope has excellent properties. Taking the 12-strand two-dimensional braided PBO rope as the research object, assuming that the cross section of the fiber bundle was circular, the braiding law and mechanical properties of the rope were studied. Using the circular braiding method for reference, the rope models with different knot diameter ratios were obtained. The representative volume elements of the rope model were intercepted and the periodic boundary conditions were applied for finite element simulation, The rope tensile experiments with different knot diameter ratios were carried out to explore the influence of knot diameter ratio on the rope strength. The simulation results were compared with the experimental results. The results show that with the increase of knot diameter ratio, the maximum tensile force that the rope increases significantly at first and then basically remains unchanged. An appropriate knot diameter ratio can effectively give play to the tensile performance of 12-strand two-dimensional braided rope, it promotes the study of mechanical properties of two-dimensional braided rope.
Two-dimensional braided rope is widely used in engineering, aerospace and many other fields, among which 12-strand two-dimensional PBO braided rope has excellent properties. Taking the 12-strand two-dimensional braided PBO rope as the research object, assuming that the cross section of the fiber bundle was circular, the braiding law and mechanical properties of the rope were studied. Using the circular braiding method for reference, the rope models with different knot diameter ratios were obtained. The representative volume elements of the rope model were intercepted and the periodic boundary conditions were applied for finite element simulation, The rope tensile experiments with different knot diameter ratios were carried out to explore the influence of knot diameter ratio on the rope strength. The simulation results were compared with the experimental results. The results show that with the increase of knot diameter ratio, the maximum tensile force that the rope increases significantly at first and then basically remains unchanged. An appropriate knot diameter ratio can effectively give play to the tensile performance of 12-strand two-dimensional braided rope, it promotes the study of mechanical properties of two-dimensional braided rope.
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000201
Abstract:
In order to meet the high requirements of future high-speed and high acceleration tactical missiles for shell bearing capacity and heat protection function, the integrated structure-heat protection ϕ480 mm composite shell was prepared by dry winding process, in which the structure layer adopted T700 carbon fiber/cyanate ester composite, and the heat protection layer adopted composite heat protection structure. The internal pressure, acoustic emission and hydraulic burst tests had been done for integrated structure-heat protection ϕ480 mm shell. The strain variation law, the damage type and damage location of Ф480mm composite shell were researched. The structural integrity of external heat protection materials was evaluated. The capacity of bearing internal pressure load was also assessed for the integrated structure-heat protection Ф480mm composite shell. The results show that the strain of Ф480mm composite shell is linear with the pressure and increased with the raising pressure. The acoustic emission signals, such as resin cracking, monofilament fracture, fiber bundle fracture and delamination are distributed in the dome aeras under the internal pressure. The Felicity ratio of ϕ480 mm composite shell is 0.96 after secondary loading. The bursting pressure of ϕ480 mm composite shell is 18.6 MPa, and the vessel characteristic coefficient reaches 42.1 km. The fiber fracture occurs in the dome areas. A small amount of fiber fuzzing, broken wire and whitening appeared on the surface of the heat resistant layer material, and no delamination and shedding occurred, maintaining good structural integrity.
In order to meet the high requirements of future high-speed and high acceleration tactical missiles for shell bearing capacity and heat protection function, the integrated structure-heat protection ϕ480 mm composite shell was prepared by dry winding process, in which the structure layer adopted T700 carbon fiber/cyanate ester composite, and the heat protection layer adopted composite heat protection structure. The internal pressure, acoustic emission and hydraulic burst tests had been done for integrated structure-heat protection ϕ480 mm shell. The strain variation law, the damage type and damage location of Ф480mm composite shell were researched. The structural integrity of external heat protection materials was evaluated. The capacity of bearing internal pressure load was also assessed for the integrated structure-heat protection Ф480mm composite shell. The results show that the strain of Ф480mm composite shell is linear with the pressure and increased with the raising pressure. The acoustic emission signals, such as resin cracking, monofilament fracture, fiber bundle fracture and delamination are distributed in the dome aeras under the internal pressure. The Felicity ratio of ϕ480 mm composite shell is 0.96 after secondary loading. The bursting pressure of ϕ480 mm composite shell is 18.6 MPa, and the vessel characteristic coefficient reaches 42.1 km. The fiber fracture occurs in the dome areas. A small amount of fiber fuzzing, broken wire and whitening appeared on the surface of the heat resistant layer material, and no delamination and shedding occurred, maintaining good structural integrity.
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000182
Abstract:
In order to achieve a kind of composite material with both wave absorbing property and certain mechanical load bearing function, the metamaterial absorbers and sandwich composite were combined. By simulation, the metamaterial absorbers satisfying dual-band and broadband electromagnetic wave absorption were designed, and the wave absorbing performances were characterized. The aforementioned metamaterial absorbers were then integrated into the sandwich composite, in which the glass fiber/epoxy composite was used as the top layer, the PMI foam was used as the core layer, and the carbon fiber/epoxy composite was used as the bottom layer. The measured electromagnetic wave absorbing performance of the final sandwich composites shows that the dual-band composite has the absorptivity of 94.13% and 99.99% at the frequency of 8.65 GHz and 10.30 GHz respectively, while the broadband composite has the absorptivity of 90.02%~99.91% at 8.25~11.61 GHz frequency range. The bending test results exhibit that the dual-band composite has the bending strength and modulus of 68.81 MPa and 7.72 GPa, and the broadband composite has the bending strength of 145.76 MPa and modulus of 9.13 GPa. The SEM photos of after-fracture cross sections show that a small area of delamination can be observed and the overall laminates bonding performance is good.
In order to achieve a kind of composite material with both wave absorbing property and certain mechanical load bearing function, the metamaterial absorbers and sandwich composite were combined. By simulation, the metamaterial absorbers satisfying dual-band and broadband electromagnetic wave absorption were designed, and the wave absorbing performances were characterized. The aforementioned metamaterial absorbers were then integrated into the sandwich composite, in which the glass fiber/epoxy composite was used as the top layer, the PMI foam was used as the core layer, and the carbon fiber/epoxy composite was used as the bottom layer. The measured electromagnetic wave absorbing performance of the final sandwich composites shows that the dual-band composite has the absorptivity of 94.13% and 99.99% at the frequency of 8.65 GHz and 10.30 GHz respectively, while the broadband composite has the absorptivity of 90.02%~99.91% at 8.25~11.61 GHz frequency range. The bending test results exhibit that the dual-band composite has the bending strength and modulus of 68.81 MPa and 7.72 GPa, and the broadband composite has the bending strength of 145.76 MPa and modulus of 9.13 GPa. The SEM photos of after-fracture cross sections show that a small area of delamination can be observed and the overall laminates bonding performance is good.
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000209
Abstract:
Using aluminum alloy ZL301 as matrix and carbon fiber laminated suture fabric as reinforcement, carbon fiber reinforced aluminum matrix (Cf/Al) composites with laminated stitch were prepared by vacuum pressure infiltration process. Through the drop hammer impact test at room temperature, the behavior of impact load and energy change with time was studied. The impact damage morphology was observed by optical microscope and industrial digital X-ray imaging system, and the impact damage mechanism was analyzed. Through the post impact compression (CAI) experiment, the residual strength of the composite along the warp direction under different impact energy was studied, the macro and micro fracture morphologies of the compressed sample were observed, and the compression failure mechanism was analyzed. The results show that the laminated stitched Cf/Al composites have significant local damage under impact load, with obvious pits appeared in the front damage area, and obvious meridional cracks appeared on the back. The crack length increases with the increase of impact energy. The main damage modes are matrix cracking and fiber fracture pulling out. The meridional compressive strength after impact decreases with the increase of impact energy. The compressed composites have transverse cracks extending from the end of the impact crack along the weft direction to the edge of the sample. The severity of yarn structure damage in the macro fracture of compression increases with the increase of impact energy, The micro fractures after compression show uneven morphology after fiber shear fracture.
Using aluminum alloy ZL301 as matrix and carbon fiber laminated suture fabric as reinforcement, carbon fiber reinforced aluminum matrix (Cf/Al) composites with laminated stitch were prepared by vacuum pressure infiltration process. Through the drop hammer impact test at room temperature, the behavior of impact load and energy change with time was studied. The impact damage morphology was observed by optical microscope and industrial digital X-ray imaging system, and the impact damage mechanism was analyzed. Through the post impact compression (CAI) experiment, the residual strength of the composite along the warp direction under different impact energy was studied, the macro and micro fracture morphologies of the compressed sample were observed, and the compression failure mechanism was analyzed. The results show that the laminated stitched Cf/Al composites have significant local damage under impact load, with obvious pits appeared in the front damage area, and obvious meridional cracks appeared on the back. The crack length increases with the increase of impact energy. The main damage modes are matrix cracking and fiber fracture pulling out. The meridional compressive strength after impact decreases with the increase of impact energy. The compressed composites have transverse cracks extending from the end of the impact crack along the weft direction to the edge of the sample. The severity of yarn structure damage in the macro fracture of compression increases with the increase of impact energy, The micro fractures after compression show uneven morphology after fiber shear fracture.
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000196
Abstract:
A Ni-Cd alloy plating is applied to the surface of steel component by brush plating, which can realize the double protection of sacrificial anode by cathodic protection and mechanical protection. The effect of concentration of Cd2+ in plating solution on the corrosion resistance of the plating was studied by using the control variable method. The corrosion potential, polarization resistance and corrosion resistance of the coating with different concentrations of Cd2+ were measured by polarization curve, AC impedance spectroscopy, full immersion corrosion test and salt solution immersion test. The results show that the co-deposition of Ni-Cd alloy with Cd of mass fraction of 15%-90t% can be realized when the mole fraction of Cd2+ changes from 0.5%-5 %, which belongs to abnormal co-deposition. When the molar fraction of Cd2+ is 4 %, that is, the mass fraction of Cd2+ in the coating is 69.40 %, and the corrosion resistance of the alloy brush coating is the best.
A Ni-Cd alloy plating is applied to the surface of steel component by brush plating, which can realize the double protection of sacrificial anode by cathodic protection and mechanical protection. The effect of concentration of Cd2+ in plating solution on the corrosion resistance of the plating was studied by using the control variable method. The corrosion potential, polarization resistance and corrosion resistance of the coating with different concentrations of Cd2+ were measured by polarization curve, AC impedance spectroscopy, full immersion corrosion test and salt solution immersion test. The results show that the co-deposition of Ni-Cd alloy with Cd of mass fraction of 15%-90t% can be realized when the mole fraction of Cd2+ changes from 0.5%-5 %, which belongs to abnormal co-deposition. When the molar fraction of Cd2+ is 4 %, that is, the mass fraction of Cd2+ in the coating is 69.40 %, and the corrosion resistance of the alloy brush coating is the best.
Properties of rosin based epoxy resin carbon fiber reinforced composites cured at medium temperature
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000187
Abstract:
Biomass maleopimaric anhydride (MPA) was used as curing agent and petroleum based E-54, AG-80 and 014U mixture was used as epoxy resin to study the thermal and mechanical properties of rosin based epoxy resin matrix and its composites, in order to further evaluate the possibility of its application in advanced resin matrix composites for main load-bearing structures of aircraft and to broaden the application field of biomass epoxy resin. The results show that the cured epoxy resin has high mechanical properties and thermogravimetric temperature. The glass transition temperature of formula F2 resin is 156 ℃, the tensile strength is 82.6 MPa, the tensile modulus is 3.05 GPa, the elongation at break is 4.2%, 5% thermal decomposition temperature is about 370 ℃. The dry glass transition temperature of composite laminates prepared from F2 / U3160 prepreg is 158 ℃ and the wet glass transition temperature is 123 ℃. The dry mechanical properties are equivalent to those of 3261 / HT3 composites which have been applied to helicopter rotor system, and have a high retention rate of wet mechanical properties.
Biomass maleopimaric anhydride (MPA) was used as curing agent and petroleum based E-54, AG-80 and 014U mixture was used as epoxy resin to study the thermal and mechanical properties of rosin based epoxy resin matrix and its composites, in order to further evaluate the possibility of its application in advanced resin matrix composites for main load-bearing structures of aircraft and to broaden the application field of biomass epoxy resin. The results show that the cured epoxy resin has high mechanical properties and thermogravimetric temperature. The glass transition temperature of formula F2 resin is 156 ℃, the tensile strength is 82.6 MPa, the tensile modulus is 3.05 GPa, the elongation at break is 4.2%, 5% thermal decomposition temperature is about 370 ℃. The dry glass transition temperature of composite laminates prepared from F2 / U3160 prepreg is 158 ℃ and the wet glass transition temperature is 123 ℃. The dry mechanical properties are equivalent to those of 3261 / HT3 composites which have been applied to helicopter rotor system, and have a high retention rate of wet mechanical properties.
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000198
Abstract:
The shape of fiber-reinforced composite work-piece cured in autoclave usually deviates from the original design after demoulding, which influences the product quality. In order to study the cure deformation law of curved parts, the geometry of conical C-shaped shell was described by only five parameters: generatrix length, radius at half height, center angle, half apex angle and shell thickness. Based on the virtual work principle and small deformation hypothesis, the analytic solution of the cure deformation caused by the temperature drop in the curing process was deduced. It is revealed that after curing, the thickness, half-height radius, generatrix length and apex angle decrease, while the center angle of the arc increases. Compared with the finite element simulation orthogonal test, which validates the analytical solution. A simplified scheme of finite element curing simulation by use of the path-dependent constitutive law is given. This simplified finite element deformation prediction method can cut the computing time by 80% and the implementation is much easier. By using this formula, thermoelastic finite element model and path-dependent finite element model, the curing deformation of the nose cover of a small fixed-wing aircraft is calculated, and the predicted average reduction of half-span length is 8.1mm,7.6mm and 6.1mm respectively, which are basically consistent with the measured value of 7.7mm. The assembly deformation characteristics of the part can also be explained based on the proposed analysis.
The shape of fiber-reinforced composite work-piece cured in autoclave usually deviates from the original design after demoulding, which influences the product quality. In order to study the cure deformation law of curved parts, the geometry of conical C-shaped shell was described by only five parameters: generatrix length, radius at half height, center angle, half apex angle and shell thickness. Based on the virtual work principle and small deformation hypothesis, the analytic solution of the cure deformation caused by the temperature drop in the curing process was deduced. It is revealed that after curing, the thickness, half-height radius, generatrix length and apex angle decrease, while the center angle of the arc increases. Compared with the finite element simulation orthogonal test, which validates the analytical solution. A simplified scheme of finite element curing simulation by use of the path-dependent constitutive law is given. This simplified finite element deformation prediction method can cut the computing time by 80% and the implementation is much easier. By using this formula, thermoelastic finite element model and path-dependent finite element model, the curing deformation of the nose cover of a small fixed-wing aircraft is calculated, and the predicted average reduction of half-span length is 8.1mm,7.6mm and 6.1mm respectively, which are basically consistent with the measured value of 7.7mm. The assembly deformation characteristics of the part can also be explained based on the proposed analysis.
2022, 42(2): 1 -10
doi: 10.11868/j.issn.1005-5053.2021.000095
Abstract:
Helicopter has achieved rapid development and wide application in various fields, due to its unique flight mode. However, the noise is also a particular feature of the helicopter, which people cannot bear without protection. With the requirements of helicopter comfort and low noise pollution, its noise has become an urgent problem that must be solved. According to the main sources and propagation ways of external noise and internal noise of the helicopter, the current situation of material and structure-based helicopter noise control in domestic and international scope was reviewed. The noise control characteristics and effects of conventional sound absorbing materials, intelligent piezoelectric control materials, acoustic super material/structure and damping material were introduced in this paper. Traditional materials are no longer suitable for the current lightweight requirements of the helicopter. Intelligent composite materials, new sound-absorbing structures, and acoustic super material/structure have become potential selections of noise suppression. Finally, combined with the current development status of helicopter vibration and noise reduction materials, the development trend of helicopter noise reduction material/structure in the future such as active noise reduction technology, resonance sound absorption, metamaterial acoustic band gap, damping material noise reduction and so on, is proposed, and feasible research ideas for the development direction of helicopter noise suppression materials/structures are put forward.
Helicopter has achieved rapid development and wide application in various fields, due to its unique flight mode. However, the noise is also a particular feature of the helicopter, which people cannot bear without protection. With the requirements of helicopter comfort and low noise pollution, its noise has become an urgent problem that must be solved. According to the main sources and propagation ways of external noise and internal noise of the helicopter, the current situation of material and structure-based helicopter noise control in domestic and international scope was reviewed. The noise control characteristics and effects of conventional sound absorbing materials, intelligent piezoelectric control materials, acoustic super material/structure and damping material were introduced in this paper. Traditional materials are no longer suitable for the current lightweight requirements of the helicopter. Intelligent composite materials, new sound-absorbing structures, and acoustic super material/structure have become potential selections of noise suppression. Finally, combined with the current development status of helicopter vibration and noise reduction materials, the development trend of helicopter noise reduction material/structure in the future such as active noise reduction technology, resonance sound absorption, metamaterial acoustic band gap, damping material noise reduction and so on, is proposed, and feasible research ideas for the development direction of helicopter noise suppression materials/structures are put forward.
2022, 42(2): 11 -19
doi: 10.11868/j.issn.1005-5053.2021.000125
Abstract:
The hot compression tests of TB9 titanium alloy sample were carried out on Gleeble-1500 thermal simulator at the temperature range of 750-1000 ℃ and the strain rate range of 0.01-10 s−1. The stress-strain curves obtained by the experiment were subjected to friction correction and the processing map was drawn according to the corrected stress-strain curve .The results show that the stress-strain curve after friction correction is obviously lower than that before correction, and the stress difference between them increased with the increase of strain. The corrected stress−strain curve is\begin{document}$ \sigma {\text{ = }}\frac{{\arcsin h{{[\frac{{\dot \varepsilon \exp (\frac{Q}{{RT}})}}{A}]}^{\frac{1}{n}}}}}{\alpha } $\end{document} ![]()
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The hot compression tests of TB9 titanium alloy sample were carried out on Gleeble-1500 thermal simulator at the temperature range of 750-1000 ℃ and the strain rate range of 0.01-10 s−1. The stress-strain curves obtained by the experiment were subjected to friction correction and the processing map was drawn according to the corrected stress-strain curve .The results show that the stress-strain curve after friction correction is obviously lower than that before correction, and the stress difference between them increased with the increase of strain. The corrected stress−strain curve is
2022, 42(2): 20 -28
doi: 10.11868/j.issn.1005-5053.2021.000159
Abstract:
The morphology and chemical composition evolution of mullite based refractory inclusions in FGH96 PM superalloy with powder state, hot isostatic pressing (HIP) and hot deformation (HF) were studied by means of artificial implantation of inclusions, optical microscopy (OM), scanning electron microscopy (SEM) and electrolytic etching. The mechanism of interfacial reaction between mullite based refractory inclusions and alloy matrix was revealed. The results show that in the powder state, the artificial mullite based inclusions are irregular particles, and there is no obvious change of morphology and composition in the inclusions after HIP process at high temperature and high pressure. A complex reaction layer is formed at the interface between inclusions and alloy matrix. The reaction layer is consisted of Al and Ti oxides. After thermal deformation of 1080 ℃/0.0004 s-1 under the condition of 25% deformation rate, the main morphology and composition of the inclusions are not changed obviously. The reaction layer coated on the inclusion began to peel and elongate from the inclusion with the deformation of the superalloy matrix, and aggregated on the side close to the elongation direction with the flow deformation of the matrix. When the deformation degree is 50%, mullite inclusions and the externally coated reaction layer are broken and deformed to form an inclusion fragments and reaction layer. The inclusions in the composite form are distributed linearly, and the long axis is perpendicular to the compression direction. When the reaction layer coated outside the inclusion is stripped and the mullite inclusion is broken to form a new surface exposed to the superalloy matrix, the reaction continues to form a new reaction layer. The crushed mullite inclusion is still dominated by O, Al and Si, but it also contains a small amount of element in the superalloy such as Ni, Cr, Ti, Co and Mo.
The morphology and chemical composition evolution of mullite based refractory inclusions in FGH96 PM superalloy with powder state, hot isostatic pressing (HIP) and hot deformation (HF) were studied by means of artificial implantation of inclusions, optical microscopy (OM), scanning electron microscopy (SEM) and electrolytic etching. The mechanism of interfacial reaction between mullite based refractory inclusions and alloy matrix was revealed. The results show that in the powder state, the artificial mullite based inclusions are irregular particles, and there is no obvious change of morphology and composition in the inclusions after HIP process at high temperature and high pressure. A complex reaction layer is formed at the interface between inclusions and alloy matrix. The reaction layer is consisted of Al and Ti oxides. After thermal deformation of 1080 ℃/0.0004 s-1 under the condition of 25% deformation rate, the main morphology and composition of the inclusions are not changed obviously. The reaction layer coated on the inclusion began to peel and elongate from the inclusion with the deformation of the superalloy matrix, and aggregated on the side close to the elongation direction with the flow deformation of the matrix. When the deformation degree is 50%, mullite inclusions and the externally coated reaction layer are broken and deformed to form an inclusion fragments and reaction layer. The inclusions in the composite form are distributed linearly, and the long axis is perpendicular to the compression direction. When the reaction layer coated outside the inclusion is stripped and the mullite inclusion is broken to form a new surface exposed to the superalloy matrix, the reaction continues to form a new reaction layer. The crushed mullite inclusion is still dominated by O, Al and Si, but it also contains a small amount of element in the superalloy such as Ni, Cr, Ti, Co and Mo.
2022, 42(2): 29 -40
doi: 10.11868/j.issn.1005-5053.2022.000010
Abstract:
Turbine blades of long-life civil aircraft and gas turbines are affected by high temperature oxidation during service, which greatly reduces the surface strength under complex working conditions and significantly shortens the service life. Therefore, oxidation resistance is one of the most specific properties that must be considered in the application of turbine blades. The influence of the different drilling processes for cooling holes on the oxidation behavior of Ni-based SX (single-crystal) superalloy at 980℃ and 1100 ℃ was investigated. The difference in the oxidation mechanism of the cooling holes under different drilling processes provided a basis for the establishment of the blade life model under service conditions. The results indicate that the film cooling holes processed by millisecond laser exhibit poor oxidation performance, and all oxidation kinetic curves basically obey the parabolic or linear law. In the initial oxidation stage of the millisecond laser specimen, the oxidation reaction is primarily determined by the growth pattern of outer NiO. Subsequently, a three-layer oxide layer（(Ni, Co)O-Spinel phase layer-α-Al2O3） gradually formed around the hole. There are relatively micro-holes under the internal α-Al2O3 layer and the γ'-free zone, which makes the oxide layer easy to exfoliate. Discontinuous α-Al2O3 is rapidly formed in the initial oxidation stage of the picosecond laser specimen, and then connected to each other to form the dense α-Al2O3 layer.
Turbine blades of long-life civil aircraft and gas turbines are affected by high temperature oxidation during service, which greatly reduces the surface strength under complex working conditions and significantly shortens the service life. Therefore, oxidation resistance is one of the most specific properties that must be considered in the application of turbine blades. The influence of the different drilling processes for cooling holes on the oxidation behavior of Ni-based SX (single-crystal) superalloy at 980℃ and 1100 ℃ was investigated. The difference in the oxidation mechanism of the cooling holes under different drilling processes provided a basis for the establishment of the blade life model under service conditions. The results indicate that the film cooling holes processed by millisecond laser exhibit poor oxidation performance, and all oxidation kinetic curves basically obey the parabolic or linear law. In the initial oxidation stage of the millisecond laser specimen, the oxidation reaction is primarily determined by the growth pattern of outer NiO. Subsequently, a three-layer oxide layer（(Ni, Co)O-Spinel phase layer-α-Al2O3） gradually formed around the hole. There are relatively micro-holes under the internal α-Al2O3 layer and the γ'-free zone, which makes the oxide layer easy to exfoliate. Discontinuous α-Al2O3 is rapidly formed in the initial oxidation stage of the picosecond laser specimen, and then connected to each other to form the dense α-Al2O3 layer.
2022, 42(2): 41 -46
doi: 10.11868/j.issn.1005-5053.2021.000101
Abstract:
The application of carbon fiber reinforced composites (CFRP) was limited by their poor delamination resistance. However, the hierarchical microstructure of flax fibers could help to improve the interlaminar properties of the composite. Therefore, the interlaminar fracture toughness of CFRP composites can be improved by hybridized flax with carbon fibers. In this study, the carbon/flax fiber hybrid composites (CFFRP) were manufactured by moulding process. The mode Ⅰand mode Ⅱ interlaminar fracture toughnesses of CFFRP composites were studied by double cantilever beam (DCB) and end-notched flexure (ENF) tests, and were compared with those of CFRP composites. The results show that the Mode Ⅰinterlaminar fracture toughness of CFFRP composite is 1.29 kJ/m2, which is about 3.5 times higher than that of CFRP composites (0.37 kJ/m2). The Mode Ⅱinterlaminar fracture toughness is 1.09 kJ/m2 and is about 23.86% higher than that of CFRP composites (0.88 kJ/m2). The interlaminar fractured surfaces of CFRP and CFFRP composites are observed with the aid of scanning electron microscopy (SEM). From the microscopies of the fractured CFRP specimens it can be seen that pure delamination by the peeling of carbon fibers from epoxy resin is obtained for CFRP composites. The surfaces of carbon fibers were relatively clean and few epoxy resin fragments attached. The weak interfacial properties between carbon fiber and epoxy resin cause a lower GⅠc for CFRP composites. On the contrary, from the observation of SEM photographs of flax fiber layers in the interlaminar fractured CFFRP composites, fiber breakage, fiber peeling and fiber entanglement are founded. On the fractured carbon fiber layer, there are some flax fibers tangling with carbon fibers. These multi-scale failure modes due to the unique microstructure of the flax fibers may make the crack propagation become difficult and thus lead to the GⅠc and GⅡc increased for CFFRP composites than those of CFRP composites.
The application of carbon fiber reinforced composites (CFRP) was limited by their poor delamination resistance. However, the hierarchical microstructure of flax fibers could help to improve the interlaminar properties of the composite. Therefore, the interlaminar fracture toughness of CFRP composites can be improved by hybridized flax with carbon fibers. In this study, the carbon/flax fiber hybrid composites (CFFRP) were manufactured by moulding process. The mode Ⅰand mode Ⅱ interlaminar fracture toughnesses of CFFRP composites were studied by double cantilever beam (DCB) and end-notched flexure (ENF) tests, and were compared with those of CFRP composites. The results show that the Mode Ⅰinterlaminar fracture toughness of CFFRP composite is 1.29 kJ/m2, which is about 3.5 times higher than that of CFRP composites (0.37 kJ/m2). The Mode Ⅱinterlaminar fracture toughness is 1.09 kJ/m2 and is about 23.86% higher than that of CFRP composites (0.88 kJ/m2). The interlaminar fractured surfaces of CFRP and CFFRP composites are observed with the aid of scanning electron microscopy (SEM). From the microscopies of the fractured CFRP specimens it can be seen that pure delamination by the peeling of carbon fibers from epoxy resin is obtained for CFRP composites. The surfaces of carbon fibers were relatively clean and few epoxy resin fragments attached. The weak interfacial properties between carbon fiber and epoxy resin cause a lower GⅠc for CFRP composites. On the contrary, from the observation of SEM photographs of flax fiber layers in the interlaminar fractured CFFRP composites, fiber breakage, fiber peeling and fiber entanglement are founded. On the fractured carbon fiber layer, there are some flax fibers tangling with carbon fibers. These multi-scale failure modes due to the unique microstructure of the flax fibers may make the crack propagation become difficult and thus lead to the GⅠc and GⅡc increased for CFFRP composites than those of CFRP composites.
2022, 42(2): 47 -56
doi: 10.11868/j.issn.1005-5053.2021.000143
Abstract:
The molecular dynamics method was employed to predict the tensile mechanical properties of polyether-ether-ketone (PEEK). Non-equilibrium tensile simulation with anisotropic pressure control was employed to obtain the stress-strain curve of PEEK, and to calculate the elastic modulus, yield strength and other mechanical properties. The influences of the strain rate and temperature on the mechanical properties, free volume, mean square radius of gyration (Rg), and energy for PEEK were investigated to explain the relationship between PEEK chain characteristics and macro mechanical properties. The results indicate that the elastic modulus and yield strength of PEEK significantly increase with the increase of strain rate, and significantly decrease with the increase of temperature. In the elastic and yield stage, free volume linearly increases, and Rg of PEEK chains remains steady, and the non-bonded energy results in the amount of the total potential energy increase. The interchain non-bonded interactions play a dominant role in the elastic and yield performance. Therefore, the amino modification strategy is investigated to improve the mechanical property of PEEK. It is found that the elastic modulus and yield strength of PEEK modified by amino are increased by 21% and 34% respectively than that of PEEK.
The molecular dynamics method was employed to predict the tensile mechanical properties of polyether-ether-ketone (PEEK). Non-equilibrium tensile simulation with anisotropic pressure control was employed to obtain the stress-strain curve of PEEK, and to calculate the elastic modulus, yield strength and other mechanical properties. The influences of the strain rate and temperature on the mechanical properties, free volume, mean square radius of gyration (Rg), and energy for PEEK were investigated to explain the relationship between PEEK chain characteristics and macro mechanical properties. The results indicate that the elastic modulus and yield strength of PEEK significantly increase with the increase of strain rate, and significantly decrease with the increase of temperature. In the elastic and yield stage, free volume linearly increases, and Rg of PEEK chains remains steady, and the non-bonded energy results in the amount of the total potential energy increase. The interchain non-bonded interactions play a dominant role in the elastic and yield performance. Therefore, the amino modification strategy is investigated to improve the mechanical property of PEEK. It is found that the elastic modulus and yield strength of PEEK modified by amino are increased by 21% and 34% respectively than that of PEEK.
2022, 42(2): 57 -63
doi: 10.11868/j.issn.1005-5053.2021.000120
Abstract:
Based on the three-point bending test, the bending performances of S6C10-800/AC318 composite unidirectional plates with different span-thickness ratios (hereinafter referred to as unidirectional plates) were tested, and the effect of span-thickness ratio on the bending strength and bending modulus of unidirectional plate was studied. The influence and fracture mode of the specimens with different span-thickness ratios were analyzed to obtain the bending failure mechanism, and the critical span-thickness ratio of three-point bending test of unidirectional plate was determined. The results show that the bending strength of the unidirectional plate increases with the increase of the span-thickness ratio, and the bending modulus first increases and then decreases with the increase of the span-thickness ratio. The fracture mode of the unidirectional plate changes when the span-thickness ratio α＝20, and the degree of delamination damage of unidirectional plate gradually decreases with the increase of span-thickness ratio, but the degree of splitting increases. When α≤20, the stress-strain curve conforms to the linear relationship with the increase of the span-thickness ratio, but when α＞20, the stress-strain curve does not conform to the linear relationship. Therefore, the predicting formula of bending strength of unidirectional plate under arbitrary span-thickness ratio and a failure criterion for three-point bending test of unidirectional plate are obtained. It is recommended that the critical span-thickness ratio of the three-point bending performance test of unidirectional plate is 20. This is of great significance for optimizing the three-point bending test method of glass fiber composite materials to more accurately test the bending performance of composite materials.
Based on the three-point bending test, the bending performances of S6C10-800/AC318 composite unidirectional plates with different span-thickness ratios (hereinafter referred to as unidirectional plates) were tested, and the effect of span-thickness ratio on the bending strength and bending modulus of unidirectional plate was studied. The influence and fracture mode of the specimens with different span-thickness ratios were analyzed to obtain the bending failure mechanism, and the critical span-thickness ratio of three-point bending test of unidirectional plate was determined. The results show that the bending strength of the unidirectional plate increases with the increase of the span-thickness ratio, and the bending modulus first increases and then decreases with the increase of the span-thickness ratio. The fracture mode of the unidirectional plate changes when the span-thickness ratio α＝20, and the degree of delamination damage of unidirectional plate gradually decreases with the increase of span-thickness ratio, but the degree of splitting increases. When α≤20, the stress-strain curve conforms to the linear relationship with the increase of the span-thickness ratio, but when α＞20, the stress-strain curve does not conform to the linear relationship. Therefore, the predicting formula of bending strength of unidirectional plate under arbitrary span-thickness ratio and a failure criterion for three-point bending test of unidirectional plate are obtained. It is recommended that the critical span-thickness ratio of the three-point bending performance test of unidirectional plate is 20. This is of great significance for optimizing the three-point bending test method of glass fiber composite materials to more accurately test the bending performance of composite materials.
Static compression and compression-compression fatigue properties of plain woven composite laminates
2022, 42(2): 64 -72
doi: 10.11868/j.issn.1005-5053.2021.000106
Abstract:
The static compression and compression-compression fatigue tests of glass fiber plain woven composite laminates were carried out on an electro-hydraulic servo fatigue testing machine. The stress ratio was R=10, and the S-N curve was fitted. The fatigue damage evolution was characterized by stiffness degradation, energy dissipation, cyclic creep and cyclic softening during fatigue tests. The fracture morphology was observed by scanning electron microscope. The results show that the conditioned fatigue limit is 66.3% of the static compressive strength. The S-N curve fitted by the double-weighted least square method has high reliability. With the increase of the number of cycles, the stiffness of the test piece decreases gradually, and the energy dissipation under each peak load increases gradually. At the initial stage of cyclic loading, the test pieces exhibit strong cyclic creep phenomenon, and the test pieces under the peak load exhibit strong cyclic softening behavior. The resistance to deformation of the test piece is enhanced after cyclic loading. Four failure modes including matrix cracking, fiber/matrix interface debonding, fiber fracture and delamination are observed. Compared with fatigue fracture, the static compression fracture shows larger delamination damage.
The static compression and compression-compression fatigue tests of glass fiber plain woven composite laminates were carried out on an electro-hydraulic servo fatigue testing machine. The stress ratio was R=10, and the S-N curve was fitted. The fatigue damage evolution was characterized by stiffness degradation, energy dissipation, cyclic creep and cyclic softening during fatigue tests. The fracture morphology was observed by scanning electron microscope. The results show that the conditioned fatigue limit is 66.3% of the static compressive strength. The S-N curve fitted by the double-weighted least square method has high reliability. With the increase of the number of cycles, the stiffness of the test piece decreases gradually, and the energy dissipation under each peak load increases gradually. At the initial stage of cyclic loading, the test pieces exhibit strong cyclic creep phenomenon, and the test pieces under the peak load exhibit strong cyclic softening behavior. The resistance to deformation of the test piece is enhanced after cyclic loading. Four failure modes including matrix cracking, fiber/matrix interface debonding, fiber fracture and delamination are observed. Compared with fatigue fracture, the static compression fracture shows larger delamination damage.
2022, 42(2): 73 -82
doi: 10.11868/j.issn.1005-5053.2021.000114
Abstract:
2.5D woven Cf/Al composites were fabricated by vacuum-assisted pressure infiltration method. Thermal shrinkage behavior and residual stress of the composites were investigated using micromechanical analysis and experimental method. The thermal expansion properties of yarn along longitudinal and transverse direction were evaluated by analytical method. Based on the yarn’s structural characteristic, the micromechanical finite element models of composites were established. The calculated macroscopic thermal strain-temperature curve from micromechanical simulation agrees well with the thermal shrinkage curve from the experiments. The simulation results indicate that the warp and weft yarns are in compressive stress state, and the residual stress on weft yarns are higher than that on the warp yarns. However, the matrix alloy is mainly in tensile stress state, and the maximum tensile stress occurs in the matrix alloy near warp yarn’s surface. The over high residual stress between the warp and weft yarns lead to local interface debonding. It is an important technical approach to reduce the residual stress in order to improve the mechanical properties of composites.
2.5D woven Cf/Al composites were fabricated by vacuum-assisted pressure infiltration method. Thermal shrinkage behavior and residual stress of the composites were investigated using micromechanical analysis and experimental method. The thermal expansion properties of yarn along longitudinal and transverse direction were evaluated by analytical method. Based on the yarn’s structural characteristic, the micromechanical finite element models of composites were established. The calculated macroscopic thermal strain-temperature curve from micromechanical simulation agrees well with the thermal shrinkage curve from the experiments. The simulation results indicate that the warp and weft yarns are in compressive stress state, and the residual stress on weft yarns are higher than that on the warp yarns. However, the matrix alloy is mainly in tensile stress state, and the maximum tensile stress occurs in the matrix alloy near warp yarn’s surface. The over high residual stress between the warp and weft yarns lead to local interface debonding. It is an important technical approach to reduce the residual stress in order to improve the mechanical properties of composites.
2022, 42(2): 83 -90
doi: 10.11868/j.issn.1005-5053.2021.000172
Abstract:
There is a problem about microstructure evolution and properties degradation for the superalloy turbine blades in long term service conditions. DZ406 alloy samples were pre-loaded to simulate the high temperature service environment of turbine blades. The thermodynamic coupling simulation conditions were 980 ℃/70 MPa, 980 ℃/110 MPa, 980 ℃/140 MPa and 980 ℃/180 MPa respectively. And then the samples were subjected to stress rupture property test at 980 ℃/275 MPa. The microstructure and 980 ℃/275 MPa rupture life of the samples under different service loading conditions were observed and analyzed. The results show that the heat treatment microstructure of DZ406 alloy is composed of carbides, residual γ +γ´ eutectic and regular γ´ phase. The morphology and size of carbides and eutectic have no obvious change with the increase of loading stress under simulated service conditions. The γ´ phase of the sample parallel to [001] direction presents different degrees of rafting, and the size of γ´ phase perpendicular to [001] direction obviously increases. The residual stress rupture life of the sample declines rapidly with the increase of service stress.
There is a problem about microstructure evolution and properties degradation for the superalloy turbine blades in long term service conditions. DZ406 alloy samples were pre-loaded to simulate the high temperature service environment of turbine blades. The thermodynamic coupling simulation conditions were 980 ℃/70 MPa, 980 ℃/110 MPa, 980 ℃/140 MPa and 980 ℃/180 MPa respectively. And then the samples were subjected to stress rupture property test at 980 ℃/275 MPa. The microstructure and 980 ℃/275 MPa rupture life of the samples under different service loading conditions were observed and analyzed. The results show that the heat treatment microstructure of DZ406 alloy is composed of carbides, residual γ +γ´ eutectic and regular γ´ phase. The morphology and size of carbides and eutectic have no obvious change with the increase of loading stress under simulated service conditions. The γ´ phase of the sample parallel to [001] direction presents different degrees of rafting, and the size of γ´ phase perpendicular to [001] direction obviously increases. The residual stress rupture life of the sample declines rapidly with the increase of service stress.
2022, 42(2): 91 -98
doi: 10.11868/j.issn.1005-5053.2021.000084
Abstract:
The process of charge accumulation and dissipation on the surface of rGO / CNTs / EP composite coating was analyzed theoretically, and the fitting analysis was carried out according to the experimental data. The rationality of the theoretical model and the factors affecting the charge dissipation were discussed. On this basis, three kinds of charge dynamic change models were adopted to fit the measured data analysis, revealed the fitting curve and charge accumulation and dissipation process parameters such as time constant, fitting coefficient, and compared with the theoretical change curve, verified the charge and time constant, the relationship between the changes of the rationality of the evaluation model with a coating of charge dissipation effect. The results show that: compared with the accumulation model, the complex model better reflects the change process of charge accumulation process. With the increase of rGO / CNTs content in the coating, the ratio of accumulation time constant to dissipation time constant increases, the peak value of accumulated charge decreases and the dissipation effect increases. The dissipation model is basically consistent with the actual trend of charge dissipation process. With the increase of rGO / CNTs content, the dissipation time constant decreases and the dissipation effect increases.
The process of charge accumulation and dissipation on the surface of rGO / CNTs / EP composite coating was analyzed theoretically, and the fitting analysis was carried out according to the experimental data. The rationality of the theoretical model and the factors affecting the charge dissipation were discussed. On this basis, three kinds of charge dynamic change models were adopted to fit the measured data analysis, revealed the fitting curve and charge accumulation and dissipation process parameters such as time constant, fitting coefficient, and compared with the theoretical change curve, verified the charge and time constant, the relationship between the changes of the rationality of the evaluation model with a coating of charge dissipation effect. The results show that: compared with the accumulation model, the complex model better reflects the change process of charge accumulation process. With the increase of rGO / CNTs content in the coating, the ratio of accumulation time constant to dissipation time constant increases, the peak value of accumulated charge decreases and the dissipation effect increases. The dissipation model is basically consistent with the actual trend of charge dissipation process. With the increase of rGO / CNTs content, the dissipation time constant decreases and the dissipation effect increases.
2016, 36(4): 89-98
doi: 10.11868/j.issn.1005-5053.2016.4.013
2016, 36(3): 13-19
doi: 10.11868/j.issn.1005-5053.2016.3.003
2020, 40(3): 77-94
doi: 10.11868/j.issn.1005-5053.2020.000061
2015, 35(4): 63-82
doi: 10.11868/j.issn.1005-5053.2015.4.010
2016, 36(3): 79-91
doi: 10.11868/j.issn.1005-5053.2016.3.009
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