Fabrication of Superhydrophobic Micro Post Array on Aluminum Substrates Using Mask Electrochemical Machining

Surfaces with controllable micro structures are significant in fundamental development of superhydrophobicity. However,preparation of superhydrophobic surfaces with array structures on metal substrates is not effective using existing methods. A new method was presented to fabricate super-hydrophobic post arrays on aluminum(Al) substrates using mask electrochemical machining and fluoridation. Electrochemical etching was first applied on Al plates with pre-prepared photoresist arrays to make the post array structures. Surface modification was subsequently applied to reduce the surface energy, followed by interaction with water to realize superhydrophobicity. Simulation and experimental verification were conducted to investigate how machining parameters affect the array structures. Analysis of the water contact angle was implemented to explore the relationship between wettability and micro structures.The results indicate that superhydrophobic surfaces with controllable post structures can be fabricated through this proposed method, producing surfaces with high water static contact angles.

Accuracy evaluation for in-situ machining reference points binocular measurement based on credibility probability

Passive binocular measurement systems are being increasingly utilized in the in-situ industries of automobiles,aviation,and aerospace,etc.due to their excellent qualities of accuracy,efficiency,and cost performance.Whereas the barrier of evaluating the accuracy of measured objects resulted from the unequal equivalent focal length and quantization of pixels,has limited their further development and application of high requirements for in-situ machining,e.g.,the measurement of machining reference points for the positioning of robotic drilling in aerospace manufacturing.In this paper,an accuracy evaluation method is proposed to address the problem.Firstly,the unequal equivalent focal length is considered to improve the accuracy of 3D reconstruction.Next,the credibility probability model is developed to calculate the probability of the observed error in the public view of the binocular measurement system and indicates the direction of improvement.Finally,the in-situ experiment is carried out to validate the method within the effective public view range of 300 mm×300 mm.The experiment results show that the RMSs of observed errors are superior to 0.035 mm,and the credibility probabilities are all higher than 0.91;the maximum 3D reconstruction accuracy improvement is 60.3%,with the error reduced from 0.078 mm to 0.031 mm.

High-precision pose measurement method in wind tunnels based on laser-aided vision technology

The measurement of position and attitude parameters for the isolated target from a highspeed aircraft is a great challenge in the field of wind tunnel simulation technology.In this paper,firstly, an image acquisition method for small high-speed targets with multi-dimensional movement in wind tunnel environment is proposed based on laser-aided vision technology.Combining with the trajectory simulation of the isolated model, the reasonably distributed laser stripes and selfluminous markers are utilized to capture clear images of the object.Then, after image processing,feature extraction, stereo correspondence and reconstruction, three-dimensional information of laser stripes and self-luminous markers are calculated.Besides, a pose solution method based on projected laser stripes and self-luminous markers is proposed.Finally, simulation experiments on measuring the position and attitude of high-speed rolling targets are conducted, as well as accuracy verification experiments.Experimental results indicate that the proposed method is feasible and efficient for measuring the pose parameters of rolling targets in wind tunnels.

A review of low-temperature plasma-assisted machining:from mechanism to application

Materials with high hardness,strength or plasticity have been widely used in the fields of aviation,aerospace,and military,among others.However,the poor machinability of these materials leads to large cutting forces,high cutting temperatures,serious tool wear,and chip adhesion,which affect machining quality.Low-temperature plasma contains a variety of active particles and can effectively adjust material properties,including hardness,strength,ductility,and wettability,significantly improving material machinability.In this paper,we first discuss the mechanisms and applications of low-temperature plasma-assisted machining.After introducing the characteristics,classifications,and action mechanisms of the low-temperature plasma,we describe the effects of the low-temperature plasma on different machining processes of various difficult-to-cut materials.The low-temperature plasma can be classified as hot plasma and cold plasma according to the different equilibrium states.Hot plasma improves material machinability via the thermal softening effect induced by the high temperature,whereas the main mechanisms of the cold plasma can be summarized as chemical reactions to reduce material hardness,the hydrophilization effect to improve surface wettability,and the Rehbinder effect to promote fracture.In addition,hybrid machining methods combining the merits of the low-temperature plasma and other energy fields like ultrasonic vibration,liquid nitrogen,and minimum quantity lubrication are also described and analyzed.Finally,the promising development trends of low-temperature plasma-assisted machining are presented,which include more precise control of the heat-affected zone in hot plasma-assisted machining,cold plasma-assisted polishing of metal materials,and further investigations on the reaction mechanisms between the cold plasma and other materials.

Analytical modeling of geometric errors induced by cutter runout and tool path optimization for five-axis flank machining

The cutter runout effect has significant influence on the shape of cutter swept surface and the machining surface quality. Hence,it is necessary to integrate the cutter runout effect in cutter swept surface modeling,geometric error prediction and tool path optimization for five-axis flank machining. In this paper,an envelope surface model considering cutter runout effect is first established,and geometric errors induced by runout effect are derived based on the relative motion analysis between the cutter and part in machining. In the model,the cutter runout is defined by four parameters,including inclination angle,location angle,offset value and the length of cutter axis. Then the runout parameters are integrated into the rotation surface of each cutting edge that is used to form the final cutter envelope surface for the five-axis machining process. Thus,the final resulting geometric errors of the machined surface induced by cutter runout can be obtained through computing the deviations from the nominal cutter swept surface. To reduce these errors,an iterative least square method is used to optimize the tool paths for five-axis flank machining. Finally,a validation example is given for a specific ruled surface. Results show the effectiveness and feasibility of the analytical model of geometric errors induced by cutter runout,and also show that the geometric errors can be reduced significantly using the proposed tool path planning method.

Simulative technology for auxiliary fuel tank separation in a wind tunnel

In this paper, we propose a simulative experimental system in wind tunnel conditions lbr the separation of auxiliary fuel tanks from an aircraft. The experimental system consists of a simulative release mechanism, a scaled model and a pose measuring system. A new release mechanism was designed to ensure stability of the separation. Scaled models of the auxiliary fuel tank were designed and their moment of inertia was adjusted by installing counterweights inside the model. Pose param- eters of the scaled model were measured and calculated by a binocular vision system. Additionally, in order to achieve high brightness and high signal-to-noise ratio of the images in the dark enclosed wind tunnel, a new high-speed image acquisition method based on miniature self-emitting units was pre- sented. Accuracy of the pose measurement system and repeatability of the separation mechanism were verified in the laboratory. Results show that the position precision of the pose measurement system can reach 0.1 mm, the precision of the pitch and yaw angles is less than 0.1° and that of the roll angle can be up to 0.3°. Besides, repeatability errors of models＂ velocity and angular velocity controlled by the release mechanism remain small, satisfying the measurement requirements. Finally, experiments for the separation of auxiliary fuel tanks were conducted in the laboratory.

Tribological properties of diamond-like carbon films deposited bv pulsed laser arc deposition

A novel method, pulsed laser arc deposition combining the advantages of pulsed laser deposition and cathode vacuum arc techniques, was used to deposit the diamond-like carbon （DLC） nanofilms with different thicknesses. Spectroscopic ellipsometer, Auger electron spectroscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, scanning electron microscopy and multi-functional friction and wear tester were employed to investigate the physical and tribological properties of the deposited films. The results show that the deposited films are amorphous and the sp2, sp3 and C-O bonds at the top surface of the films are identified. The Raman peak intensity and surface roughness increase with increasing film thickness. Friction coefficients are about 0.1, 0.15, 0.18, when the film thicknesses are in the range of 17-21 nm, 30-57 nm, 67-123 nm, respectively. This is attributed to the united effects of substrate and surface roughness. The wear mechanism of DLC films is mainly abrasive wear when film thickness is in the range of 17-41 nm, while it transforms to abrasive and adhesive wear, when the film thickness lies between 72 and 123 nm.

Region Pair Grey Difference Classifier for Face Detection

A new kind of region pair grey difference classifier was proposed. The regions in pairs associated to form a feature were not necessarily directly-connected, but were selected dedicatedly to the grey transition between regions coinciding with the face pattern structure. Fifteen brighter and darker region pairs were chosen to form the region pair grey difference features with high discriminant capabilities. Instead of using both false acceptance rate and false rejection rate, the mutual information was used as a unified metric for evaluating the classifying performance. The parameters of specified positions, areas and grey difference bias for each single region pair feature were selected by an optimization processing aiming at maximizing the mutual information between the region pair feature and classifying distribution, respectively. An additional region-based feature depicting the correlation between global region grey intensity patterns was also proposed. Compared with the result of Viola-like approach using over 2 000 features, the proposed approach can achieve similar error rates with only 16 features and 1/6 implementation time on controlled illumination images.

Simulation and prediction in laser bending of silicon sheet

The laser bending of single-crystal silicon sheet (0.2 mm in thickness) was investigated with JK701 Nd:YAG laser. The models were developed to describe the beam characteristics of pulsed laser. In order to simulate the process of laser bending, the FEM software ANSYS was used to predict the heat temperature and stress-strain fields. The periodic transformation of temperature field and stress-strain distribution was analyzed during pulsed laser scanning silicon sheet. The results indicate that the mechanism of pulsed laser bending silicon is a hybrid mechanism in silicon bending, rather than a simple mechanism of TGM or BM. This work also gets silicon sheet bent after scanning 6 times with pulsed laser, and its bending angle is up to 6.5o. The simulation and prediction results reach well agreement with the verifying experiments.

Laser-assisted grinding of RB-SiC composites:Laser ablation behavior and mechanism

Laser ablation is an important process during Laser-Assisted Grinding(LAG)of hard and brittle materials.To realize controllable material removal during laser ablation of RB-SiC composites,ablation experiments under different Laser Energy Density(LAED)and LAG experiments are conducted.Evolution rules and mechanism of physical phase,ablation morphology and crack characteristics caused by laser irradiation are investigated.The forces of LAG and Conventional Grinding(CG)are compared.The results show that ablation surface changes from slight oxidation to obvious material removal with LAED increasing,and ablation depth increases gradually.The ablation products change from submicron SiO_(2)particles to nanoscale particles and floccule.High LAED promotes SiC decomposition and sublimation,which leads to the increase of C element.The SiC phase forms corrugated shape in recast layer and columnar shape in Heat Affected Zone(HAZ)at 56 J/mm^(2).The cold and heat cycle leads to formation of fishbone crack.For ablation specimen under 30 J/mm^(2),the grinding force can be reduced by a maximum of 39%and brittle damage region is reduced.The material removal and microcrack generated will significantly reduce the hardness and improve machinability,which can promote grinding efficiency.

Adaptive estimation and nonlinear variable gain compensation of the contouring error for precise parametric curve following

Contour following is one of the most important issues faced by many computer-numerical-control(CNC) machine tools to achieve high machining precision. This paper presents a new real-time error compensation method aiming at reducing the contouring error caused by facts such as servo lag and dynamics mismatch in parametric curved contour-following tasks. Due to the lack of high-precision contouring-error estimation method for free-form parametric curved toolpath, the error can hardly be compensated effectively. Therefore, an adaptive accurate contouring-error estimation algorithm is proposed first, where a tangential-error backstepping method based on Taylor's expansion is developed to rapidly find the closest point on the parametric curve to the actual motion position. On this foundation, the contouring error is compensated using a proposed nonlinear variable-gain compensation method, where the compensation gain is obtained according to not only the contouring-error magnitude but also its direction variation. The stability of the system after compensation is analyzed afterwards according to the Jury stability criterion.By design of the compensator in accordance with the presented contouring-error compensation method as well as the stability analyzation result, the balance between the response speed and the contour control stability can be effectively made. Experimental tests demonstrate the feasibility of the presented methods in both contouring-error estimation and contour-accuracy improvement.Contributions of this research are significant for enhancing the contour-following performance of the CNC machine tools.

Facile and Economical Fabrication of Superhydrophobic Flexible Resistive Strain Sensors for Human Motion Detection

Superhydrophobic flexible strain sensors have great application value in the fields of personal health monitoring,human motion detection,and soft robotics due to their good flexibility and high sensitivity.However,complicated preparation processes and costly processing procedures have limited their development.To overcome these limitations,in this work we develop a facile and low-cost method for fabricating superhydrophobic flexible strain sensor via spraying carbon black(CB)nanoparticles dispersed in a thermoplastic elastomer(SEBS)solution on a polydimethylsiloxane(PDMS)flexible substrate.The prepared strain sensor had a large water contact angle of 153±2.83°and a small rolling angle of 8.5±1.04°,and exhibited excellent self-cleaning property.Due to the excellent superhydrophobicity,aqueous acid,salt,and alkali could quickly roll off the flexible strain sensor.In addition,the sensor showed excellent sensitivity(gauge factor(GF)of 5.4–7.35),wide sensing ranges(stretching:over 70%),good linearity(three linear regions),low hysteresis(hysteresis error of 4.8%),and a stable response over 100 stretching-releasing cycles.Moreover,the sensor was also capable of effectively detecting human motion signals like finger bending and wrist bending,showing promising application prospects in wearable electronic devices,personalized health monitoring,etc.

An active damping vibration control system for wind tunnel models

In wind tunnels, long cantilever sting support systems with low structural damping encounter flow separation and turbulence during wind tunnel tests, which results in destructive low-frequency and big-amplitude resonance, leading to data quality degradation and test envelope limitation. To ensure planed test envelope and obtain high-quality data, an active damping vibration control system independent of balance signal based on stackable piezoelectric actuators and velocity feedback using accelerometer, is proposed to improve the support stability and wind tunnel testing safety in transonic wind tunnel. Meanwhile, a design of powerful sting-root embedded active damping device is given and an active vibration control method is presented based on the mechanism analysis of aircraft model vibration. Furthermore, a self-adaptive fuzzy Proportion Differentiation(PD) control model is proposed to realize control parameters adjustment automatically for various testing conditions. Besides, verification tests are performed in laboratory and a continuous transonic wind tunnel. Experimental results indicate that the aircraft model does not vibrate obviously from -4° to 11° at Ma = 0.6, the number of useable angle-of-attack has increased by 7° at Ma = 0.6 and 5° at Ma = 0.7 respectively, satisfying the requirements of practical wind tunnel tests.

Tribological properties of La_2O_3 and CeO_2 doped CoCrW coatings deposited by supersonic plasma spraying

A novel supersonic plasma spraying was used to prepare rare earth oxides doped CoCrW coatings. X-ray diffractometer, contact surface profiler, hardness tester, micro-friction and -wear tester and en- vironmental scanning electron microscope equipped with energy dispersive X-ray spectroscopy were employed to investigate the phase structure, surface morphology, microhardness, friction and wear properties of the sprayed coatings. The results show that rare earth oxide doped coatings have high microhardness and excellent tribological properties. Furthermore, the friction and wear mechanisms of sprayed coatings are also discussed.

A multi-order method for predicting stability of a multi-delay milling system considering helix angle and run-out effects

In this paper, a multi-delay milling system considering helix angle and run-out effects is firstly established. An exponential cutting force model is used to model the interaction between a work-piece and a cutting tool, and a new approach is presented for accurately calibrating exponential cutting force coefficients and cutter run-out parameters. Furthermore, based on an implicit multi-step Adams formula and an improved precise time-integration algorithm, a novel stability prediction method is proposed to predict the stability of the system. The involved time delay term and periodic coefficient term are integrated as a comprehensive state term in the integral response which is approximated by the Adams formula. Then, a Floquet transition matrix with an arbitraryorder form is constructed by using a series of matrix multiplication, and the stability of the system is determined by the Floquet theory. Compared to classical semi-discretization methods and fulldiscretization methods, the developed method shows a good performance in convergence, efficiency,accuracy, and multi-order complexity. A series of cutting tests is further carried out to validate the practicability and effectiveness of the proposed method. The results show that the calibration process needs a time of less than 5 min, and the stability prediction method is effective.

An active vibration control method based on energy-fuzzy for cantilever structures excited by aerodynamic loads

In wind tunnel tests for the full-model fixed with sting,the low structural damping of the long cantilever sting results in destructive low-frequency and large-amplitude vibration.In order to obtain high-quality wind tunnel test data and ensure the safety of wind tunnel tests,an energy-fuzzy adaptive PD(Proportion Differentiation)control method is proposed.This method is used for active vibration control of a cantilever structure under variable aerodynamic load excitation,and real-time adjustment of parameters is achieved according to the system characteristics of vibration energy.Meanwhile,a real-time method is proposed to estimate the real-time vibration energy through the vibration acceleration signal,and the average exciting power of aerodynamic load is obtained by deducting the part of the power contributed by the vibration suppressor from the total power.Furthermore,an energy-fuzzy adaptive PD controller is proposed to achieve adaptive control to the changes of the aerodynamic load.Besides,the subsonic and transonic experiments were carried out in wind tunnel,the results revealed that comparing to fixed gain PD controllers,the energy-fuzzy adaptive PD controller maintains higher performance.

Remote-controlled flexible pose measurement system and method for a moving target in wind tunnel

The measurement of position and attitude parameters for the isolated target from a highspeed aircraft is a great challenge in the field of wind tunnel simulation technology. This paper proposes a remote-controlled flexible pose measurement system in wind tunnel conditions for the separation of a target from an aircraft. The position and attitude parameters of a moving object are obtained by utilizing a single camera with a focal length and camera orientation that can be changed based on different measurement conditions. Using this proposed system and method, both the flexibility and efficiency of the pose measurement system can be enhanced in wind tunnel conditions to meet the measurement requirements of different objects and experiments, which is also useful for the development of an intelligent position and attitude measurement system. The position and the focal length of the camera also can be controlled remotely during measurements to enlarge both the vertical and horizontal measurement range of this system. Experiments are conducted in the laboratory to measure the position and attitude of moving objects with high flexibility and efficiency, and the measurement precision of the measurement system is also verified through experiments.

An error analysis and optimization method for combined measurement with binocular vision

The accurate measurement of surfaces of large aviation components is vital for the assessment of manufacturing and assembly quality of such components.To satisfy the measurement requirement of large-size components,most current researches pay more attention to combined measurement methods utilizing different measuring instruments,but the related researches on error analysis and optimization methods are not taken enough attention.This paper proposes a combined laser-assisted measurement method with feature enhancement techniques,and it also develops an error propagation model of the main factors affecting the overall measurement error in detail.Firstly,the surface of a large-size component is measured by the measurement system at multiple stations.Secondly,a control point coordinate system is established as a bridge to unify all local measurement data into the global coordinate system.To improve the overall measurement accuracy,the pixel extraction error as a key factor causing the overall measurement error is analyzed in detail.Next,the error propagation model is established,and some optimization strategies of layout for minimizing measurement error and transformation error are researched.Finally,experiments are carried out to verify the effectiveness of the proposed method.The results show that the measurement error of the proposed method reaches 0.073%and 0.14%with a 1 D standard ruler and a flat plate,respectively.

An experimental system for release simulation of internal stores in a supersonic wind tunnel

Aerodynamic parameters obtained from separation experiments of internal stores in a wind tunnel are significant in aircraft designs. Accurate wind tunnel tests can help to improve the release stability of the stores and in-flight safety of the aircrafts in supersonic environments.A simulative system for free drop experiments of internal stores based on a practical project is provided in this paper. The system contains a store release mechanism, a control system and an attitude measurement system. The release mechanism adopts a six-bar linkage driven by a cylinder, which ensures the release stability. The structure and initial aerodynamic parameters of the stores are also designed and adjusted. A high speed vision measurement system for high speed rolling targets is utilized to measure the pose parameters of the internal store models and an optimizing method for the coordinates of markers is presented based on a priori model. The experimental results show excellent repeatability of the system, and indicate that the position measurement precision is less than0.13 mm, and the attitude measurement precision for pitch and yaw angles is less than 0.126°, satisfying the requirements of practical wind tunnel tests. A separation experiment for the internal stores is also conducted in the FL-3 wind tunnel of China Aerodynamics Research Institute.