The nitrogen content in the weld of high nitrogen steel is an important factor affecting its mechanical properties. It is a fact that mechanical properties of weld deteriorate with the decrease of nitrogen content in welding of high nitrogen steel. In order to solve this problem, the laser arc hybrid welding experiment was carried out on 12 mm thick high nitrogen steel plates, and the effect of nitrogen content on the microstructure and mechanical properties of weld was studied by changing filler materials. Results show that the use of nitrogen-containing welding wire can effectively supplement and the nitrogen loss in the weld. The nitrogen content of welding seam of nitrogen welding wire is higher in the laser zone, the nitrogen content of both welding wires increases with the increase of laser power. The weld microstructure of the two kinds of welding wires is austenite and a little ferrite. The tensile strength of stainless steel welding wire increases with the increase of laser power, and the tensile strength of nitrogen-containing welding wire first increases and then decreases with the increase of laser power. The maximum tensile strength reaches 953 MPa. The fracture surface of weld shows typical ductile fracture characteristics. The weld impact properties of the two kinds of welding wires are quite different, and the impact fracture has obvious ductile fracture characteristics.

The low-alloy high-strength steel was welded by the laser wire filler welding, and the effects of laser power, wire feeding speed and defocus amount on the stability of the welding process were studied by high-speed camera, and a good welded joint was obtained with optimized process parameters. The results show that reducing the laser power or increasing the wire feed speed can reduce the porosity; When the defocus amount is 0 mm, the porosity is the lowest. The welding stability depends on the droplet transfer mode. When the droplet transfer mode is liquid bridge transfer, the welding stability of laser wire filling is improved. The wire melting zone of the laser wire filling welding joint is austenite and martensite dual-phase structure, and the laser action zone is a martensite single-phase structure. The microhardness of the laser zone is higher than that of the wire melting zone.

In order to explore the feasibility of low-power laser welding of steel and aluminum, a fiber laser was used to conduct laser brazing experiments of aluminum on the top and steel on the bottom with 1 mm thick 6061 aluminum alloy and 1.2 mm thick DP600 dual-phase steel as the test objects. The effects of laser power and welding speed on weld quality (joint formability, weld microstructure and mechanical properties) were investigated. Results show that the tensile strength of the joints first increases and then decreases with the increase of laser power and welding speed. The maximum tensile strength of the welded joint is 127 N/mm, the fracture shows typical brittle fracture characteristics, and the thickness of intermetallic compound is about 10 μm, under the laser parameter with power of 405 W, welding speed of 5 mm/s. The study provides certain technical support for improving the quality of laser welding. The effects of laser power and welding speed on joint formability, weld microstructure and mechanical properties esults show that the tensile strength of the joints first increases and then decreases with the increase of laser power and welding speed.

Laser self-fusion welding was used to weld Q235 ordinary carbon steel and 304 austenitic stainless-steel dissimilar steel, and the effects of different welding parameters on microstructure and mechanical properties of dissimilar steel welded joints were studied. Experimental results show that high quality welding seam and small heat affected zone can be obtained due to the high concentration of laser energy density. According to the element content obtained from the direct reading spectrum, and refer to the Schaeffler diagram, it can be inferred that the microstructure of the weld area is composed of martensite. Metallographic microscope and scanning electron microscope were used to verify that the weld seam is mainly composed of lath martensite. The microhardness tests show that the microhardness of weld zone is higher than that of base metal on both sides. Under the condition of sufficient heat input and complete penetration of welded joint, tensile fracture occurs on the side of Q235 steel of base metal, which indicates that the strength of welded joint is higher than that of base metal if the welding heat input is insufficient, there will be incomplete fusion defects and even air holes in the weld joint, and the tensile fracture of welded joint occurred in the weld zone.

The same transparent polyethylene terephthalate (PET) plastic was welded by laser transmission welding using the 1 710 nm diode laser. Because the transparent PET plastic has a high absorption rate for 1.7 μm laser, there is no need to use laser absorber in the welding process. The influence of energy input on welding strength was discussed by adjusting laser power and welding speed. When the laser power is 10 W and the welding speed is 7.5 mm/s, the aesthetic and strong welding parts are obtained with the energy input is 1.33 J/mm. Keeping this energy input constant, a comparative experiment was designed by changing laser power in the range of 5-30 W. Results show that the change of laser power (5-30 W) and welding speed (3.75-22.50 mm/s) has little effect on the weld strength of the welding specimen.

Fe55 alloy coatings were prepared on Q235 steel substrate by laser cladding and TIG surfacing, respectively. The microstructure and properties of the coating were studied by means of OM, X-ray diffraction, microhardness and abrasive wear. Results show that the dilution ratios of laser cladding and TIG surfacing coatings are 4.42% and 7.65%, respectively, and they are composed of α-Fe solid solution and in-situ synthesized particle reinforced phases, such as CrFeB,Cr7C3,(Cr,Fe)7C3 and Fe2B. The microstructure of laser cladding coating is mainly dendrite and cellular crystal, and the microstructure of TIG surfacing coating is mainly equiaxed crystal and cellular crystal. The microstructure of laser cladding coating is finer and denser than that of TIG surfacing coating. The microhardness and wear resistance of laser cladding coating are better than those of TIG surfacing coating, and the average microhardness is about 664 HV, and the main wear mode is micro cutting.

When the engine block is in service, there will be external dust particles accompanied by diesel and gasoline into the cylinder block, wear and corrosion damage the surface of the engine block, affecting the performance of the engine. In order to repair the cylinder body surface, a wide-band laser cladding head with output spot size of 15 mm×3 mm was used to repair the engine cylinder body surface by single-channel wide-band laser cladding experiment. The cladding base material is 42CrMo steel, and the cladding powder material is Fe316L. The influence of parameters, such as laser power, powder feeding speed, air flow and scanning speed, on the cladding quality and the weight of each parameter are studied, and when the best process parameters are obtained as laser power 4 250 W, powder feeding speed 3 r/min, and air flow 5.1 L/min and scanning speed of 459 r/min and cladding at the focal point, the cladding quality is higher. The surface roughness of the cladding layer is 2.19 μm, and the microhardness of the cladding layer is 552.9 HV.

Ti6Al4V alloy samples were prepared by selective laser melting, and the effect of microstructure on mechanical properties was systematically studied by optical microscope, scanning electron microscopy and fracture morphology analysis. Comparing the microstructure characteristics under different parameters, the microstructure features show that columnar β crystal is formed along the deposition direction, and the acicular martensite α′ phase is mainly distributed in the crystal. With the increase of α′ phase content, the plasticity becomes worse. By controlling the process parameters, the acicular martensite α′ decomposes in situ to form α + β phase, which is conducive to improving the plasticity. By controlling the laser power and scanning speed, samples with excellent comprehensive mechanical properties were prepared. The tensile strength reached 1 301 MPa, the yield strength reached 1 102 MPa, and the elongation was 7.94%. Tensile properties can be improved by microstructure regulation of in-situ analysis for titanium alloy manufactured by selective laser melting.

TC4 titanium alloy was formed by selective laser melting (SLM) process. The influence of laser power P and scanning speed V on the density and surface hardness of multilayer parts was studied by using two-factor controlled variable method from the aspect of input energy density. Experimental results show that when the energy density per unit volume of powder is 119.05 J/mm3<φ<166.67 J/mm3, the density of the molded parts can reach 96.62%～97.41%, and the surface microhardness can reach 415.2～425.4 HV, which is higher than the microhardness of powder particles before molding 335.4 HV. When the laser power is P=200 W, the scanning speed is V=600 mm/s, the powder thickness is H=0.04 mm, and the scanning distance is S=0.06 mm, the density of the formed parts reaches 97.41%, the surface microhardness reaches 440.5 HV, and the formed titanium alloy parts have good mechanical properties.

Hard composite materials are often used as alloy materials for tool production due to their high hardness, high strength and good wear resistance. In this paper, selective laser melting (SLM) technology was used to prepare WC 12Co cemented carbide samples by changing the forming process parameters, laser power and scanning speed, and the effects of process parameters on the density, cross-section metallographic structure and microhardness of the formed samples were studied. Results show that when the laser scanning speed value is constant, with the increase of the laser power, the density of the molded sample shows a gradually increasing trend. When the laser power value is constant, with the increase of the laser scanning speed, the density of the molded sample first increases and then decreases, and the scanning speed has a more obvious influence on the density; too large or too small line energy density is not conducive to the increase of the sample density. When the laser power is 290 W, the scanning speed is 900 mm/s under the optimal parameter combination, a WC 12Co sample with a density of 91.392% was obtained. Through reasonable matching design of process parameters, it provides theoretical and process practical reference for the application of SLM molding WC 12Co in actual industrial production.

To investigate high cycle fatigue properties of Ti6Al4V alloys, Ti6Al4V alloy specimens were manufactured by laser powder bed fusion (LPBF) at different laser powers, and the Ti6Al4V alloys prepared at the optimal process parameters were heat treated. The surface morphology, the microstructure evolution and the static tensile and dynamic fatigue properties of heat-treated Ti6Al4V alloy specimens are investigated. The surface of as-fabricated Ti6Al4V specimens prepared at a laser power of 300 W appears smooth without apparent pores and cracks. The phases of as-fabricated Ti6Al4V specimens change from the needle-like α′ martensite to a coarsened α+β lamellar mixture upon heat treatment. The fatigue strength of heat-treated Ti6Al4V alloys reaches a value of 567.5 MPa at a stress ratio of 0.06 and 107 cycles. The propagation rate da/dN of fatigue crack and the stress intensity factor ΔK show a linear relationship in the stable propagation region.

To guarantee the comprehensive mechanical properties of laser additive repaired 15-5PH parts can meet the operating requirements, laser cladding experiment is carried out with optimized process parameters, and the microstructure and mechanical properties of cladded layer and heat affected zone (HAZ) are analyzed. Results shows that the microstructure of the cladded layer is columnar dendrite growing perpendicular to the track joint. In addition to Martensite, there are a small amount of residual austenite and ferrite. The average microhardness of the cladded layer is about 355 HV, showing relatively high strength and plasticity while yield strength is low. Microstructure are refined in phase transformation zone, and microhardness increased gradually from the bonding interface, reaching peak value (about 420 HV) at the depth of 0.5 mm. High-temperature tempered area are found below phase transformation zone, in which microhardness decreases to about 360 HV and gradually restore to the level of substrate. Tempered area is narrow, which has little influence on the mechanical properties of the substrate. The plasticity of the sample in HAZ is slightly improved while maintaining high tensile strength. The tensile properties of the laser additive repaired sample (with 50% cladded layer in thickness) is close to that of the heat treated substrate.

In order to study the heat, stress and deformation in the process of laser coaxial powder feeding additive connections of large component, and to explore their distribution laws and evolution characteristics, ANSYS parametric design language is used to realize the finite element numerical simulation of the connecting processes through programming. Results show that the proportion of the joint area is small so that the heat affected zone will be concentrated around the joints. When the distance between the joints is close, the heat affected zone will be overlapped. The stresses at the joints have different characteristics in the connection stage and cooling stage. The stress values are not high, and the stress concentration is not obvious during connecting. At the initial stage of cooling, the stresses increase and at the same time tend to be concentrated. After a period of time, the stress will be stable at the high position, and the concentrated high stress zones will be formed at the joints. Under the boundary conditions, the longitudinal warpage of the frame is obvious, and the shape error will occur after the cylindrical hole is connected. Because there is only the deformation compatibility between the roots and the frame, the rib plates deflect in different directions and angles. The connection positions and constraint modes have great influence on the forming accuracy.

In order to explore the influence of various technological factors of the laser oblique shock peening on the peening effect and deformation of FGH95 superalloy aircraft turbine disk tenon material. In this paper, laser energy, spot diameter and impact times, as three main technological factors, were selected for carrying out orthogonal test of three factors and three levels. The surface residual stress and bending deformation indicators of the peened specimens were detected, and the obtained data were analyzed by range and variance analysis, to discuss the regularity and the significance of the influence of various technological factors on the various indicators. Experimental results show that, in the case of this paper, significance order of the various factors influencing the size of the surface residual compressive stress is: laser energy > impact times > spot diameter. Significance order of the various factors influencing the degree of bending deformation is: impact times > spot diameter > laser energy, while laser energy is 8 J, spot diameter is 3 mm, impact times is 1. The bending deformation degree of FGH95 superalloy is relatively minimum, and the higher surface residual compressive stress can be obtained, which can meet the actual processing quality requirements. Therefore, smaller deformation and optimum surface properties can be obtained when the laser oblique shock peening process parameters are appropriately matched.

In the course of service, the power fittings often fail prematurely because of the complex service environment. In order to further improve the service life of the power fittings, in this paper, laser quenching and flame quenching were used to strengthen the surface of the samples. The microstructure and hardness of surface hardening layer under different treatment methods were studied. The wear resistance was tested by a friction and wear tester, and the surface wear morphology and wear mechanism were analyzed. Results show that after laser quenching and flame quenching, the wear resistance of the original samples is improved in different degrees. The weight loss after laser quenching is reduced by 80.60%, and the wear degree is slight. The weight loss after flame quenching is reduced by 66.24%, and the wear mechanism is abrasive wear. The wear mechanism of untreated samples is dominated by adhesion wear.

The WC/Co coating was deposited on the surface of 37Mn5 steel by selective laser melting（SLM）. The wear resistance of WC/Co coating was tested by potentiostatic method, and the electrochemical corrosion performance was tested by seawater as medium. Results show that WC/Co coating produces diffraction peaks corresponding to (111), (200) and (311) crystal faces. The thickness of WC/Co coating is about 3 μm, which forms a rough surface structure, and scratches occur under the action of load. When the load is 5 N, the polarization curve shifts to the lower right corner, the corrosion potential also increases significantly, the corrosion current density is smaller, and the current density in the anode region significantly fluctuates. After increasing the anode potential, the passivation film has been broken down and produced microholes, resulting in a significant increase in current. When the potential of WC/Co coating increases, the friction coefficient increases, which leads to the corrosion of the coating and the increasement of wear amount. When the potential is 0.5 V, the coating has been worn through, forming a large number of pitting pit structures, scratching furrows, and a few peeling occurred at the boundary of the wear mark.

The effect of laser process parameters on the cleaning quality of the surface paint of T300 carbon fiber was studied, and a CO2 laser was used to perform laser cleaning tests on the samples. The shape measuring laser microscope was used to measure the surface roughness and removal thickness of the sample after laser cleaning. The influence under different average laser power, overlap ratio and scanning times was studied. Through mechanical property analysis, paint adhesion test, aging test, temperature test and metallographic test, the results show that: the overlap rate of the laser average power and the spot is too large, which will cause certain damage to the carbon fiber surface. When the average laser power P=40 W, the spot overlap rate δ=65%, and the number of scans t=1, good laser cleaning quality can be achieved without affecting the mechanical properties of the material. The cleaned surface can meet the quality requirements of subsequent repainting. The research can provide technical reference for the engineering application of laser cleaning CFRP in aircraft manufacturing field.

Based on the optical refraction characteristics of transparent solid medium, the error analysis of the traditional method for measuring the refractive index of transparent solid using laser speckle is carried out, and an improved method to reduce the error is proposed. Firstly, an image speckle measurement system has been set up with the transparent solid placed between the imaging lens and CCD. After that, the two speckle patterns are collected by the CCD when the transparent solid is placed perpendicular to the optical axis and deflecting to a certain angle respectively. A speckle in-plane displacement can be obtained by processing the above two speckle patterns using the digital image correlation method. Finally, the refractive index of solid can be calculated based on the theoretical formula. According to the comparison experiments, the measurement results show that this improved method has smaller error and higher precision.

In order to realize the quantitative characterization of pipe defects by laser ultrasonic technology, the interaction process of ultrasonic wave generated on the surface of metal pipe irradiated by laser and pipe defects was analyzed by finite element method. This paper explores the mode conversion of ultrasonic in the transmission process through the transmission image, and it also discusses the influence of defects with different height, width and angle on laser ultrasonic in the way of far-field excitation. Combined with the displacement signal of the receiving point, this paper analyzes the complex process of the interaction between ultrasonic and defects, and it analyzes the corresponding causes by applying Huygens principle. Finally, it puts forward a pipeline defect determination method Methods of quantitative characterization. The theoretical conclusion is verified by experimental research. The experimental research and theoretical conclusions show that the defect position can be quantitatively characterized by the receiving time of the reflected echo signal generated after the surface wave encounters the defect, the defect depth can be quantitatively characterized by the receiving time of the reflected surface wave signal generated at the bottom of the defect, and the defect angle can be quantitatively characterized by the defect angle. The quantitative characterization of the reception time of the bottom surface wave converted longitudinal wave signal lays a theoretical foundation for the reverse estimation of the size of the defect.

Differential optical absorption spectroscopy (DOAS) technology can accurately and real-time monitor the concentration of flue gas components, which is an effective means to control the emission of flue gas pollutants from the source. In DOAS system, the change of light source intensity is an important factor affecting the long-term reliability of measurement. In order to solve this problem, a new DOAS retrieval algorithm without calibration of light intensity is proposed in this paper. The algorithm uses the neighbouring wide-band cross section to normalize the narrow-band cross section of gas characteristic absorption, so as to obtain the equivalent absorption intensity parameter, αeq(λk), which is not affected by the change of light source intensity. By comparing the measured value of this parameter with the calculated value of standard cross section, the gas concentration can be calculated. Compared with the traditional algorithm, this algorithm does not need complex calculation such as polynomial fitting and signal filtering, and it is more convenient for hardware implementation. The measurement system was built, and N2 and high concentration NO standard gas were used to prepare different concentrations of NO. The measurement results show that the characteristic absorption of NO only appears in 195.5 nm (absorption 1), 204.7 nm (absorption 2), 214.8 nm (absorption 3), 226.2 nm (absorption 4), and the full width at half maximum of the four absorptions are about 1 nm. The linear regression coefficient R2 of characteristic absorption 4 (226.2 nm) reaches the maximum of 0.998 17, which verifies the feasibility of the new method.

The current dynamic target recognition methods cannot collect enough feature information in complex images, which leads to the limitation of the application of recognition results. Based on 3D laser point cloud, a moving image dynamic target recognition method is proposed. The 3D scanning system is used to obtain the image features of point cloud, and the image preprocessing is carried out without affecting the effective information acquisition. The ground plane equation is introduced, and the image background point cloud and the identified target point cloud are segmented by Euclidean clustering method. The key points of the identified target are extracted after processing, and the Freeman chain code is used to detect the edge features, so as to complete the dynamic target recognition of the moving image. Experimental results show that the dynamic target recognition method based on three-dimensional laser point cloud has good identification ability, good recognition accuracy and short dynamic target recognition time.

Due to the structure and process control during the production process of tank containers, it is necessary to measure geometric dimensions, such as the roundness of the inner container. This paper proposes a method for obtaining the roundness of the inner container based on the three-dimensional laser scanning method. Firstly, the full-scale point cloud of the inner container is obtained by scanning; and the internal stiffener plates, pipes and other accessories point cloud are removed based on the normal vector algorithm. Secondly, the positive angle of the point cloud is calculated through the tube section ellipse fitting to achieve high-precision registration. Finally, using RANSAC central axis fitting and Euclidean distance calculation, the roundness of different cross-sections of the inner container point cloud is obtained. Compared with manual measurement, the accuracy of this method is better than 2 mm, and the measurement time is about 10 minutes, which improves measurement efficiency and reduces labor intensity. It provides a solution for 3D laser scanning for process measurement.

In order to prevent point cloud noise from the surrounding environment and signal interference during the reconstruction of the architectural landscape, a visual art reconstruction method of the architectural landscape based on 3D laser printing is proposed. Kinect is used to obtain point cloud data on the surface of the object, and multi-view alignment and point cloud denoising processing are conducted to make the model data more accurate. The iterative nearest point algorithm is used to perform point cloud registration and fusion of the data, and data preprocessing is performed. The point cloud data is fused into a smooth surface model without holes. According to the three-dimensional model of the architectural landscape, the visualization system using 3D laser printer printing technology realizes the model. The simulation test results show that the error rate of the designed architectural landscape reconstruction is below 10%, and the smooth value of the reconstruction data is maintained at about 0.9, which meets the requirements of the visual art reconstruction of the architectural landscape.

In order to improve the modeling accuracy of urban gardens and other types of landscapes, a 3D landscape modeling method is designed based on the laser 3D point cloud technology. Laser three-dimensional point cloud stereo non-contact measurement technology is used to obtain the three-dimensional coordinates of the landscape surface data points. The point cloud data of all angles are unified in a coordinate system, the longest distance between sequential points is used as the filter standard, and the point is set beyond the standard. In order to fix the endpoints and smoothly process the image point cloud, the triangular mesh parameterization strategy is used to map the three-dimensional mesh model to the two-dimensional plane to obtain the texture coordinates of the characteristic points. The harmonic mapping algorithm is used to solve the texture coordinates of the unconstrained points. By partially adjusting the strategy, the texture of the point cloud data is optimized and the final landscape model is obtained. The experiment collects three-dimensional data of a landscape in the study area, and combines the effects of the landscape model and the evaluation index to find out. The proposed method can effectively develop the model with high accuracy, and the detailed information of the model is relatively complete.

Fixed pattern noise(FPN) is a kind of common noise in complementary metal oxide semiconductor(CMOS) camera sensors, which has an adverse impact on the image quality of the camera. In order to improve the quality of road disease detection images, this paper proposes a fixed-mode noise removal algorithm of CMOS image sensor based on combined filtering. Firstly, the mean filtering is used to extract the spatial distribution characteristics of the fixed-mode noise of the CMOS sensor camera. Secondly, the proposed linear filtering method is used to remove most of the fixed mode noise. Finally, nonlinear filtering is used to remove salt and pepper noise. Experimental results show that the peak signal-to-noise ratio (PSNR) of the three groups of test images is between 28.75 and 32.50, and the mean square error of the images decreases from 9.66 to 11.28 before processing to 5.45 to 7.59 after processing. The mean square error of the processed images was reduced by 27.68% to 43.61%. The proposed algorithm can effectively reduce the influence of fixed pattern noise in CMOS sensor camera on image quality and retain the main texture features of road damage images, which has higher practicability compared with the traditional calibration method for CMOS sensor camera.

This paper investigates the influence of thickness and minority carrier lifetime of multiplication layer and absorption layer on dark current, based on InGaAs/InP avalanche photodiode. Results demonstrated that the thickness of absorption layer mainly affects shockley-read-hall (SRH) and trap-assisted tunneling (TAT) dark currents, while the thickness of the multiplication layer mainly affects TAT and band-band tunneling (BBT) dark currents. The minority carrier lifetime, equivalent to the defects effect, plays a role in SRH and TAT dark currents. Analysis of dark current mechanisms could provide a well theoretical prediction for avalanche devices with low dark current and high signal-to-noise ratio.

Laser lipolysis technology is in a relatively preliminary stage, and the current research lacks the parameter information applicable to human body. In the process of laser lipid dissolving, temperature, as an important quantity, is difficult to be monitored in real time. In this paper, the effects of 1 064 nm Nd: YAG continuous laser on the temperature rise of pig fat were studied through a series of experiments in combination with the multi-channel grating optical fiber temperature measurement system. The experimental scheme of continuous fat dissolution was designed and verified. Results show that the transmissive power of 1 064 nm Nd: YAG laser in fat is less than 2 mm. The heat distribution generated by the photothermal effect is also concentrated in the radial and axial tissues within 5 mm. In addition, the temperature distribution is closely related to the power density and irradiation time of the fat laser. After the irradiation temperature reaches 35 ℃, the parameters that keep the temperature within the safe range within a certain period of time are: power density 27.08 W/cm2, irradiation time 16 s, natural cooling 9 s; power density 40.62 W/cm2, irradiation time 9 s, natural cooling 9 s.