As an essential branch of metal additive manufacturing, wire and arc additive manufacturing (WAAM), using an arc as the energy beam, is suitable for rapidly fabricating medium-to-large scale metal components and exhibits a wide application prospect in aerospace and national defense. Nevertheless, the issues of low forming accuracy, poor process stability and difficult defect control restrict high-efficiency and high-quality development and application of this technology.
It has been urgently to implement online monitoring and closed-loop control during the entire WAAM process for the demand of reliable, automatic, and quality-ensured manufacture. The characteristic parameters and their main influential factors are analyzed. Principles and research status of process sensing methods are illustrated. Control methods of forming quality in WAAM are summarized. Eventually, principal developing orientations of process sensing and control in WAAM are proposed.

Blade tip timing technology is a non-contact measurement technology that is popular in recent years and can be used for the health monitoring of the entire stage, which provides the possibility for online monitoring and fault diagnosis of rotor blade vibration. Aiming at the common rubbing faults of rotor blades, the single-blade and whole-stage dynamic models were established respectively, and the dynamic responses of the blade tips under the rubbing faults of the above two models were analyzed. The characteristics of the blade tip timing signals of sensors and blades in the state of rubbing were expounded, and the feature extraction of the undersampling signal of the blade tip timing was carried out by the enhanced sparse decomposition algorithm. A set of procedures for diagnosing rubbing faults was proposed. The effectiveness of the proposed method is verified by a self-built rubbing test bench.

Sonic IR imaging enjoys the advantages of precise defect positioning, high thermal SNR (signal to noise ratio), material suitability, etc. It has shown good capabilities of detecting defects in aeronautical materials and key components, such as engine blades, landing gears, wings, honeycomb sandwiched structures, etc. Firstly, the working principle and system configuration of sonic IR imaging are introduced. Then, the development of sonic IR imaging is reviewed from seven main aspects, i.e., vibration characteristic, heating characteristic, simulation modelling, testing condition, thermal image processing & defect identification, defect detectability, and application. The features of sonic IR imaging are also highlighted. Additionally, a detailed description of defect detection for aeronautical metals and composites is summarized. Finally, the future trends of sonic IR imaging are discussed, which provide certain references for its research and application in testing aeronautical materials.

The grain size of metal materials is an important parameter for the characterization of mechanical properties. Realizing the online detection of grain size plays an important role on improving product quality, upgrading intelligent factories, and intelligent scheduling. Firstly, the experimental platform of laser ultrasonic online nondestructive testing based on the thermoelastic mechanism was introduced in this paper. Then the modeling methods characterizing grain size based on frequency domain energy attenuation, and the grain size and distribution based on spectral attenuation, were analyzed. Finally, the experimental simulation of some environmental disturbance was carried out. The online detection of grain size based on laser ultrasonic technology is realized, and the detection accuracy can reach more than 86%. When the sample movement is within 20 mm/s, the out-of-plane jitter is ±7 mm and the deflection angle is within 0.8°, the detection results can be effectively ensured.

In this paper, shearography and thermography have been used in detecting inner defects of the fiber reinforced resin matrix composite fairing shell. Shearography and infrared thermography are contactless nondestructive testing methods based on distinct disciplines. Under the same thermal excitation, these two methods are able to be applied to nondestructive testing. In this study, an image fusion technique has been proposed to expand the dynamic range of digital camera to meet the requirement for smooth surface of the fairing shell. Based on a low-cost thermography setup, a phase enhancement scheme has also been developed for on-situ nondestructive evaluation. Shearography and infrared thermography have been conducted on the fairing by means of thermal excitation. The experimental results show that the proposed fusion method is helpful in dealing with the uneven distribution of light intensity due to laser illumination and surface condition; and the infrared phase enhancement scheme greatly improves the visibility of defects. These two methods possess individual advantages. Based on the experiment, an assessment about these two optical methods is conducted, which provides valuable experiences in subsequent  defect detections.

It is urgent and important for online detection and evaluation of metallurgical quality during metal additive manufacturing in the aerospace field. The research status and progress of online ultrasonic testing technology of metal additive manufacturing at home and abroad were summarized. The design principle and the composition of the self-developed laser ultrasonic multi-metallurgical feature synchronous online detection system were introduced. The laser ultrasonic testing experiments were conducted using the self-developed system for the components manufactured by laser additive manufacturing. The size of coarse clusters of α-phase grains with preferred crystal orientation in laser melting deposited TC4/B4C composites was quantitatively evaluated based on the spectral centroid frequency shift of laser ultrasonic longitudinal wave pulse echoes. Then, the surface defects of laser melting deposited AlSi10Mg aluminum alloy were detected. The signal-to-noise ratio of the online real-time detection signal was improved by combining two methods. First, multiple laser pulses were excited at each measuring point in the scanning detection for averaging. Second, the twostep denoising method by combining the improved wavelet threshold and with variational mode decomposition was used. Based on the energy variation of surface wave pulse signals, the hole with a diameter of 0.5 mm and the horizontal crack with the width of 0.5 mm were imaged.

The independent component analysis method was used to study the defect characterization problem of composite impact damage based on pulsed infrared images. First, according to the prior knowledge of pulse infrared experiment of test block and the temperature difference between defect and non-defect, the appropriate interval segment was selected for infrared sequence image. Then, centering preprocessing and whitening preprocessing were performed on the constructed data matrix, independent component analysis was performed by gradient descent method, and the independent component feature image can be obtained by reconstructing the matrix. Finally, by choosing an appropriate image segmentation method, the defect characterization quantities of the maximum damage long diameter and damage short diameter can be obtained. Taking the damage defect extraction of two carbon fiber reinforced composite laminates with different thicknesses under the impact energy of 30 J and 40 J, as an example, the maximum damage long diameter and damage short diameter of impact damage were successfully extracted and compared with the results of ultrasonic F-scan.  For comparison, the errors are within an acceptable range, especially for the laminate with a thickness of 2 mm, which errors are within 5%. The research results showed that independent component analysis can effectively distinguish noise from defects, and the obtained feature image has higher signal-to-noise ratio, greater contrast and better image quality than the original image, which is beneficial to the extraction and characterization of defects.

The tasks of docking the aircraft wing parts and finishing holes have difficulties such as the quality of the assembly object, the number of finishing holes required, and the need for processing at the assembly site. In order to solve the above problems, a docking and finishing system for large aircraft parts is designed. Under the positioning of the digital measurement system, the AGV platform loads and transports the large parts of aircraft wing, and cooperates with the posture positioning system to perform the posture adjustment and docking of the wing and the fuselage, and the hole finishing system finishing the holes. After experimental verification, the positioning error of the system is less than 0.1% of the stroke, and the dimensional accuracy of the finished hole meets the IT7 accuracy. In the large-scale hole finishing, it takes 36 h for docking and finishing a total of 150 holes, which confirms the feasibility of deploying in the actual production line.

Carbon-based composite materials (C/C, C/SiC) have high specific strength, high specific modulus, low density, low thermal expansion coefficient, corrosion resistance, thermal shock resistance, and are considered as one of the most promising high temperature structural materials. However, carbon-based composites generally begin to oxidize at 500 ℃, and have large porosity, which cannot achieve high pressure sealing, which greatly limits the application prospects ofcarbon-based composites. Under the environment of high temperature and high pressure air scour, ultra high temperature ceramic base protective coating can effectively inhibit carbon composite material (C/C, C/SiC) in the degradation of carbon composition. The melting point of hafnium carbide (HfC) is as high as 3890 ℃, which is the highest in the known single compound, the thermal conductivity is only 5.6 W/(m · K), Vickers hardness is as high as 26 GPa, good ablative resistance, but also has low thermal conductivity, low oxygen diffusion coefficient, low surface vapor pressure. Oxidation resistant ablative coatings have been used as extremely heat resistant components such as rocket nozzles and nose cones. In this paper, the research background, basic properties, preparation technology, ablation mechanism and coefficient of thermal expansion are summarized. The current challenges of ultra temperature ceramic HfC coatings are pointed out, and the development trend of ultra temperature ceramic HfC coatings is forecasted.

Aiming at the accurate microstructural control of turbine disk during hot forging, the evolution of microstructure under sudden increase of strain rate was investigated by finite element method. The constitutive models for flow stress, dynamic recrystallization and metadynamic recrystallization of a turbine disk material were implemented into finite element software. Then the hot compression of a cylindrical sample and single and multi-pass forging of a turbine disk were simulated. The results show that the sudden increase of strain rate can induce the occurrence of pseudometadynamic resrytallization. i.e., the suspension of dynamic recrystallization as a consequence of nucleation inhibition. The finite element method may have some shortcomings in microstructural prediction under sudden increase of strain rate. It is easier to achieve the target grain structure in the core area of turbine disk. The sudden increase of strain rate at key area should be avoided during single pass forging. The degree of recrystallization can be improved by multi-pass forging.

Carbon fiber reinforced polymer (CFRP) has the characteristics of multi-scale and multi-equal structure, showing significant anisotropy and heterogeneity, poor machining performance, and easy to appear obvious burrs and delamination. In order to analyze the characteristics in helical milling of CFRP, the ball helical milling of CFRP was studied, and cutting forces, tool wear and hole-making quality were analyzed in detail. First, based on the result of the experiment, the changes of axial and radial cutting force and cutting temperature over cutting parameters were analyzed.  Then, tool wear was studied respectively from the lateral edge and spherical edge. Finally, hole diameter was analyzed from the perspective of the hole deep, entry and exit hole-making quality, and delamination factor was used to describe entry delamination state. The results show that the ball end milling cutter has better cutting characteristics in the ball helical milling of CFRP, but hole-making quality needs to be improved.

Based on the wire laser additive manufacturing, this paper innovatively proposes a new process of additive manufacturing of laser wobble fuse combined with laser swing welding technology. Firstly, the laser power P, wire feeding speed V_s, and printing speed V_p are controlled in the process without laser swing, and the appropriate swing frequency f, swing amplitude A and overlap rate η are adjusted under circular swing. A single-channel experiment was performed on TC4 titanium alloy, and it was found by comparison that the deposition quality was better when P = 2500 W, V_s = 3 m/min, V_p = 2.5 m/min, f = 300 Hz, A = 1 mm and η = 50%. Based on the single-pass experiment, multi-pass multilayer printing was carried out, and the microstructure and phase of the as-deposited state and after annealing were analyzed by XRD, TEM, SEM and EBSD. The results show that the microstructures are mainly slender acicular martensite α′ and initial columnar β grains under single-pass printing and multi-layer multi-pass printing. In addition, the β grains are irregular in shape, the growth orientation changes obviously, the α′ size is small, and the structure is closely arranged, which is a typical widmanstetten structure. After recrystallization annealing (800 ℃/2 h, furnace cooling), the grain boundary of α phase appears, and the α phase tends to grow.