The bolted joint is the most common connection method for composite structures in aircraft. Due to the characteristics of the composite bolted joint itself and the complexity of the load and service environment, it is very difficult to analyze the integrity and durability of the composite bolted joint. It is very challengeable to effectively and intelligently monitor the service condition of composite bolted joints in real time, as well as to diagnose and evaluate their reliability and integrity on-line. In this paper, the damage monitoring technology of advanced carbon fiber reinforced composite bolted joint based on flexible eddy current sensor array film and carbon-based nanopiezoresistive sensor is proposed and developed. The sensor monitoring principle, the sensor preparation process, and the sensor-bolt integration scheme are systematically described. In order to verify the monitoring functions of the proposed advanced sensing techniques, a series of experiments are conducted, and the experimental results show that these advanced sensing techniques have a good ability to identify damage patterns and quantify damage parameters.
The graded material structure has broad application prospects in aerospace, medical implants, energyabsorbing structures, etc. for its excellent mechanical properties and energy absorption. A graded minimal surface porous structure design method is proposed by imitating the structure of bamboo with graded structure, and linearly graded Gyroid structures and topological density graded Gyroid structures were designed based on this method. The porous structures were manufactured by laser powder bed fusion technology, and the bending properties of the uniform structure and graded structure were analyzed by bending test and digital image correlation technology. The experimental results show that the bending elastic modulus of the Gyroid porous structure is a linear function of porosity, and the critical porosity of bending fracture is between 80% and 85%. The linear graded porous structure has the asymmetric bending behavior like bamboo, and it has the highest bending toughness and no bending fracture when the porosity is distributed in the form of 70%→90%, while it has the highest bending strength when the porosity is distributed in the form of 90%→70%, which is 36.08% higher than the bending strength of the uniform Gyroid structure with porosity of 80%. It is demonstrated that bending deformation and fracture mode can be adjusted by the graded distribution mode of porosity. A structure with lightweight and high bending strength can be obtained by the reasonably graded structure design.
Thermal barrier coatings are the key materials for high temperature components of aero turbine engines. The coating flaking failure under severe service conditions and multi-field coupling is the key problem to be solved urgently. The research and development of service environment test simulation device is an inevitable way to solve this problem, and also an important means and method to improve the coating performance. In this paper, the research status of the test simulation device is reviewed in detail from the aspects of single service environment and multi-coupling service environment. The static test device and dynamic test device are mainly described. Finally, the key scientific issues to be studied in the future are analyzed, and the development trend of the service environment simulation test method of thermal barrier coatings is prospected.
The CaO–MgO–Al2O3–SiO2 (CMAS) corrosion behavior of zirconia-based materials doped with different YO1.5 contents (8YSZ, 20YSZ, 38YSZ, 55YSZ) and pure yttrium oxide materials (Y2O3) at 1300 ℃ has been systematically studied. The results show that the CMAS corrosion behavior of zirconia-based materials with different yttria contents is significantly different. For 8YSZ and 20YSZ with low YO1.5 content, the corrosion behavior is dominated by solutionreprecipitation and grain boundary corrosion. The former precipitates ZrO2 grains, while the latter precipitates directly deposited on the surface of the original ZrO2 to form a core-shell structure. With the increase of YO1.5 content, the corrosion behavior gradually changed into reactive corrosion. The rapid reaction crystallization of 38YSZ and 55YSZ with CMAS molten salt formed a continuous dense protective layer containing apatite phase, which could effectively block the further erosion of CMAS molten salt. Moreover, the volume fraction of apatite phase in the protective layer formed by 55YSZ was more, which has better corrosion resistance to CMAS. Pure Y2O3 samples can also react quickly with CMAS molten salt to form a dense pure apatite layer, which has good corrosion resistance to CMAS molten salt. Therefore, the resistance of thermal barrier coatings to CMAS molten salt corrosion can be controlled by adjusting the yttrium content in zirconia-based materials.
Thermal barrier coatings (TBCs) are widely used in the hot end components of advanced aero-engines, effectively prolong the service life of the hot end components, and become essential thermal protection materials for advanced aero-engines. However, in the process of service, some atmospheric sediments CMAS became molten after heating and adsorbed on the surface of the thermal barrier coating, and penetrated into the coating along the defects such as pores and cracks, leading to premature failure of the coating. YSZ thermal barrier coating was prepared by plasma spraying–physical vapor deposition (PS–PVD). XRD, SEM and other characterization methods were used to characterize the phase composition and microstructure of the coating with different corrosion time. The results show that YSZ coatings undergo phase transition after CMAS corrosion at 1250 ℃ . With the increase of corrosion time, CMAS sediments will penetrate into the interior along the columnar crystal gap of the thermal barrier coating, resulting in loose coating structure, columnar crystal fracture phenomenon in the upper region of the ceramic layer, and the coating macro performance is part of the ceramic layer spalling. After 8 h of corrosion, columnar crystals appear in some areas of the ceramic layer and peel off from the bonding layer. The penetration depth of CMAS increases with the increase of corrosion time. The penetration rate of CMAS is relatively fast within 3 h of corrosion, but becomes relatively slow after 3 h of corrosion.
As an advanced structural material widely used in aerospace field，environmental barrier coatings are necessary for ceramic matrix composites in actual service environment. Tantalate is a promising environmental barrier coating material due to its excellent high-temperature thermo-mechanical properties and a thermal expansion coefficient of ((3.5–5.5)×10–6 K–1) suitable for ceramic matrix composites. (AlTa)xB2–2xO4/(RE–Al)TaO4 composite coatings were successfully prepared on the surface of silicon carbide fiber reinforced silicon carbide matrix composites (SiCf /SiC) by atmospheric plasma spraying (APS) process. The optimum heat treatment conditions of the coating were explored. At the same time, the thermal fatigue test and bending strength test of composite coating samples with different coating structure schemes were carried out at 1300 ℃ , and the coating structure with the best thermal fatigue resistance was selected. The surface morphology, crack propagation and element distribution of the coating were analyzed and characterized by XRD, SEM and metallographic microscope. Compared with the traditional coatings, the tantalate composite coating has become a potential environmental barrier coating due to its excellent comprehensive performance at high temperature.
Molding is an important process for thermoplastic composites to prepare products, and the surface quality of molding is an important reference for the overall quality evaluation of products. Based on the study of the basic characteristics of polyphenylene sulfide carbon fiber prepreg, this paper adopts the self-designed right angle mold and temperature control system to carry out the molding test of satin fabric prepreg and unidirectional prepreg, and comprehensively considers the influence of heating temperature, mold temperature, cooling time, pressure, ply and bending angle on the molding appearance. The results show that the prepreg is more conducive to resin impregnation in a specific temperature range, and it can keep a certain viscosity without outflow; The reasonable combination of cooling and pressure can make the molding surface more smooth and bright. The unidirectional prepreg layer will affect the surface quality of molding, while the fabric prepreg has little effect; During molding, the local shape change of the product is more likely to produce quality defects, and the excessive design of sharp corners or large curvature should be avoided as far as possible.
SiCp/Al composites play an important role in aerospace, precision instruments and other fields, however, higher cutting force and cutting temperature will appear in the machining process, thus reducing the surface quality and precision of the turning process. In order to explore the effect of ultrasonic elliptic vibration and turning technological parameters on SiCp/Al turning, the SiCp/Al ultrasonic elliptic vibration finite element turning simulation model was established in ABAQUS, the SiCp/Al micro-geometric modeling method was optimized, the turning model was verified and the simulation experiment was carried out. The results show that the ultrasonic elliptic vibration turning can effectively reduce the defects such as subsurface damage and surface crack. It is found that with the increase of cutting speed and cutting depth, the main cutting force and cutting temperature of conventional and ultrasonic turning increase; The ultrasonic elliptical vibration technology can effectively reduce the main cutting force and cutting temperature in SiCp/Al turning process. Among the selected parameters, the ultrasonic effect reduces the cutting force the most when the cutting depth is 100 μm and the cutting speed is 200 mm/s; The ultrasonic effect reduces the cutting temperature the most when the cutting depth is 20 μm and the cutting speed is 600 mm/s.
Yttria partially stabilized zirconia (YSZ), a component of thermal barrier coatings, is widely used in complex high temperature conditions. The excellent thermal durability is attributed to non-transformable tetragonal phase (t′). Currently, it is uncertain for the maximum working temperature of t′ phase, and the mainstream view is still around 1200 ℃. Based on this, using atmospheric plasma spray (APS) process, YSZ coatings were fabricated followed by various thermal aging treatment. Evolution of microstructure, phase composition, sintering shrinkage and fracture toughness were investigated. The results show that the coating tested in 24 h@1400 ℃ still maintains m phase free even after 7–year room temperature storage; samples heat treated at 300 h@1400 ℃ and 300 h@1600 ℃ no broken, with m phase volume content of 3.55% and 35.41%, respectively. The average linear shrinkage of 300 h@1600 ℃ heat treated coatings is 0.4%. Grain growth and pore healing occurred during thermal aging treatment, bringing the increase of the bending strength and fracture toughness of coatings. Therefore, APS YSZ coatings can be used at 1400 ℃ for long time (~300 h) service.
Carbon fiber reinforced polymer (CFRP) has become the preferred material for weight reduction and efficiency improvement in the aerospace field due to its light weight and high strength. Curing is the key to manufacture CFRP components with both geometry and load-bearing properties. Compared with the traditional conduction heating curing/repairing method, the microwave heating curing/repairing method has the advantages of sensitive temperature control, short period, and low energy consumption. However, microwave resonates to form standing waves in the cavity, which makes a large number of cold and hot spots exist in the CFRP laminated plates, and the temperature is not uniform. The components are easy to deform, and even partial ablation or incomplete curing occurs in serious cases. In this paper, a temperature field control method for microwave curing of CFRP laminates with multi-frequency energy dispersion was proposed. By dispersing the energy required for heating into microwaves of various frequencies, the influence of the standing wave of a single frequency was weakened. Meanwhile, the superposition effect between standing waves of various frequencies was utilized to improve the temperature uniformity of CFRP laminates during microwave curing. The experimental results show that the maximum temperature difference of CFRP laminates was reduced by 26% compared with single-frequency microwave heating when only 915 MHz and 2.45 GHz microwave heating were used.
Micro/nano-indentation is a very important technique to characterize the mechanical properties and elastic/plastic response behavior of ceramic coatings system. A thermal barrier coating model containing randomly distributed circular pores was developed in ABAQUS using a secondary development plugin Python to investigate the effect of pores on the micro/nano-indentation response of thermal barrier coatings prepared by atmospheric plasma spraying (APS). Based on a finite element model of a thermal barrier coating containing random circular pores, the extended finite element method was used to simulate and analyze the crack propagation within the ceramic layer during the icro/nanoindentation experiments, and to further investigate the interaction between micro-cracks and pores, and the patterns of crack emergence and propagation within the coating. The results show that the distribution characteristic of the residual stress could be changed due to existence of the pores because the pores would release some stress concentration more or less during the loading and unloading processes. The presence of pores in the ceramic layer caused cracks to propagate in the direction of the pores and prevented crack further propagate to some extent. Correlating this work with the experimental results from micro/nano-indentation experiments may help us to predict the actual mechanical properties of thermal barrier coating systems.
As an efficient and cost-effective new process method, near-net shape blade is increasingly being used in the manufacture of aero-engine blank. For aero-engine near net-shape blade, which is complex and thin-walled part, it is not possible to ensure that all areas are formed at once and meet the design accuracy requirements, and adaptive machining of the leading/trailing edge areas is required. The leading/trailing edge surfaces in adaptive machining are often reconstructed surfaces that have large curvature variations and uneven boundaries due to measurement data, leading/trailing edge areas shape constraint, blank deformation and other factors. To address the above problems, this paper analyses the geometric relationship between tool centre path and machined surface, and establish a planning line planning algorithm for the smooth tool centre path based on the smooth offset surface to achieve efficient automatic generation of smooth tool centre path for reconstructed surface. The experimental results show that the surface contour tolerance is controlled within the range of (–0.02~+0.039) mm to meet the requirement of the design tolerance (–0.03~+0.05) mm, which proves the effectiveness and practicality of the proposed method.
