Double laser welding technology was used to weld the T-joints of TC2 and TA15 titanium alloys, and the joints were heat-treated at 650 ℃ to remove the stress. The microstructure of the joints were analyzed, and the mechanical properties of the joints were tested. The effect of heat treatment process and vertical bars on the mechanical properties of joints. Results showed that after heat treatment at 650 ℃, the mechanical properties of TA15 titanium alloy joints remained basically unchanged, while the mechanical properties of TC2 titanium alloy joints were slightly reduced after heat treatment. This is mainly due to the obvious recovery and recrystallization of the TC2 structure after heat treatment. The tensile properties of TC2 joints are better than those of the base metal due to the presence of the studs. Because the grain orientation of the joints is at a certain angle with the fiber direction of the original base metal, which is no longer perpendicular to the direction of the shear test force, the shear performance is higher than that of the base metal. But the 650 ℃ heat treatment has little effect on the mechanical properties of the joint. The tensile mechanical properties of the force perpendicular to the direction of the vertical bars are not significantly improved by only 2%, while the shear performance of the force perpendicular to the direction of the vertical bars is significantly improved by about 25%.

Aiming at the low precision of welding seam appearance inspection, a welding seam appearance feature detection method based on optical low coherence was proposed. The three-dimensional coordinate information of the appearance of the weld was obtained by optical low coherence measurement principle, and the three-dimensional contour of the weld was extracted by filtering algorithm. Based on the characteristics of weld contour, DBGBCA algorithm was proposed to classify the point set to determine the fitting interval. After using RANSAC algorithm for linear fitting, the fitting interval and fitting order of polynomial are accurately adjustedfor curve fitting. Based on linear fitting and curve fitting, the characteristic points were determined, and the appearance parameters of the weld were obtained. Experimental results show that the accuracy of the proposed method can be up to 0.004 mm, which meets the requirements of industrial production.

In order to simulate the repair of rail gaps and cracks, a U-shaped groove was prepared on the U75V rail base material for laser filler wire welding repair. The optimized repair process parameters obtained were: laser power P=5 000 W, welding speed 500 mm/min, wire feeding speed 200 cm/min, defocus +20 mm, Z-axis lift 0.75 mm/track. The acicular martensite structure exists in the heat-affected zone of the weld after welding. After the high temperature tempering treatment at 600 ℃ for 1 h, the acicular martensite is transformed into tempered sorbite structure. After tempering, the tensile strength and hardness of the weld are close to that of the base material, and the friction coefficient is slightly higher than that of the base material, but it still meets the requirements of actual working conditions.

High entropy alloys (HEAs) have very extensive application value. At present, traditional iron-based alloys cannot achieve the effect of high-speed cutting. In order to improve the performance of traditional tool materials in high-speed cutting, laser cladding technology was used to modify the traditional tool materials. In this paper, the previous researches are reviewed, and the preparation methods and research status of HEAs blocks and coatings are also summarized. This work is based on thermodynamic semi-empirical criterion for alloy composition design. The microstructure and properties of the basic alloy system under the composition design are introduced, and the influence mechanism of adding different elements on the microstructure and properties of the coating is explored. Secondly, the effect of annealing and process parameters on microstructure and properties of high melting point and high entropy alloy coating by laser cladding on tool surface is introduced. Finally, the development prospect of high melting point high entropy alloy coating is prospected.

Aming at the study on deformation analysis of laser cladding technology, laser cladding shaft deformation have been rarely investigated， a set of simplified ladder axis was designed, and the corresponding experiment was carried out. Through the measurement and analysis of the circular runout of different measuring position of stepped shaft under different cladding paths, the optimal cladding path with minimum deformation is obtained. Finally, the correctness of the experimental results is verified by the finite element analysis using ANSYS software.

In order to improve the comprehensive properties of TC4 titanium alloy surface, laser cladding experiments were conducted on the surface of TC4 alloy material to synthetically prepare a wear-resistant composite coating using Fe35A alloy powders. Subsequently, digital testing equipment was used to study and analyze the comprehensive properties of the coating, such as Rockwell hardness, macroscopic morphology and geometry. Test results demonstrated that the best quality of the cladding layer was achieved with the optimum cladding parameters of 2 300 W laser power, 9 mm/s scanning speed and 10 g/min powder feeding rate. The macroscopic morphology is regular and full, the surface Rockwell hardness value is up to 40.2 HRC, and the surface of the cladding layer is uniform. This paper achieved the effect of high quality cladding coating of Fe35A alloy on the surface of TC4 titanium alloy.

In this paper, orthogonal experiments are used to study the effects of the four parameters of laser power, scanning speed, powder thickness, and scanning spacing on the surface roughness and side roughness of TC4 titanium alloy molded parts during the rapid prototyping by laser melting and the influence law of surface hardness. Results show that the important order of the four parameters on the upper surface roughness is laser power, scanning speed, coating thickness, and scanning distance, and the important order of influence on the side surface roughness is laser power, powder thickness, scanning speed, and scanning spacing. The important order of influence on surface hardness is laser power, powder thickness, scanning spacing, and scanning speed. Experimental results show that the optimized process parameters for forming the surface quality of TC4 molded parts are laser power 200 W, scanning speed 600 m/s, spreading thickness 0.04 mm, scanning distance 0.06 mm.

Focus on the urgent need to improve the wear resistance of Deloro40 nickel-based alloy, which is a valve material in the nuclear industry, this paper uses laser additive manufacturing technology to explore the effect of Mo on the microstructure and wear resistance of Deloro40 nickel-based alloy by adding different contents of Mo. Results show that the addition of Mo promotes the formation of Mo2C, Mo2O and Ni3Si2 phases. With the increase of Mo content, fine grain size and hard phase Mo2C formed in microstructure improve the hardness of the alloy. The wear rate of samples increased first and then decreased. MoO2 generated in the friction process played a lubrication role, which reduced the wear rate. It shows excellent wear resistance at 25 ℃ and 400 ℃ when 5% Mo was added.

The micro-blind hole technology of flexible circuit board is a key part of high density interconnection fabrication process. In this paper, a 355 nm UV laser was used to drill the double-sided flexible copper clad plates. The effects of UV laser power and scanning speed on the morphology and quality of blind holes of two kinds of flexible coppers (electrolytic copper and calendered copper) were studied. It is found that the laser power and scanning speed have direct effect on the quality of the blind hole. Results show that when the laser power is 4.5 W and the scanning speed is 50 mm/s for calendering copper, and the laser power is 5.5 W and the scanning speed is 150 mm/s for electrolytic copper, the quality of the blind hole is the best.

This study aims at investigating the optimization of laser cutting Ni-based alloy, which is an important aerospace material. Firstly, the quality of laser cutting Ni-based alloy under variation of process parameters is evaluated by orthogonal experiment. The optimized parameters are analyzed intuitively and evaluated as 80.175. After that, the feedback neural network is used to train and fit the cutting quality, and samples of 17 and 18 are predicted that their error percentage of cutting quality are 3.14% and 2.20%, respectively. Finally, the genetic algorithm is used to optimize the extreme value based on this neural network model. The optimal fitness value and strain value within the population range are obtained through crossover operation with probability of 0.4 and mutation operation with probability of 0.2. The iterative evolution process is 100 times, and the theoretical score is 89.076. The actual score obtained by the verification experiment is 89.150, and the error percentage is only 0.074. Compared with orthogonal analysis and optimization, this method can quickly find the best process parameters with only a few experimental samples.

As an intrinsically safe gas detection method, laser gas telemetry can perform real-time, online, non-contact, and long-distance detection, which has unique advantages. Based on non-cooperative Targets, a portable, lightweight, low-cost and practical handheld laser methane telemeter with completely independent intellectual property rights has been designed and developed. The temperature control chip of the telemeter adopts WTC3243 and the temperature control accuracy can reach 0.01 ℃. The transceiver integrated optical telemetry component of the telemeter adopts a parallel optical axis design. Through the standard gas comparison test, results show that the relative measurement error is within ±5%, the comprehensive measurement deviation is 293×10-6 m, and the goodness of fit between the telemeter measurement value and the standard integral concentration value is up to 0.999. After different telemetry distance tests, results show that the telemetry distance can reach 20 m, and the system has the consistency of different telemetry distance measurements. By simulating the actual environment test of methane leaking air mass, results show that the designed and developed handheld laser methane gas telemeter can be used for real-time, online, non-contact, and remote sensing of methane gas leakage in actual gas pipelines and other places, which also meets the measurement requirements.

Time discrimination circuit is an important part of lidar. It is used to detect the termination time of the echo pulse signal reaching the receiver and inform the processor for data processing. In order to meet the requirements of lidar system for accurate time identification of time identification circuit, this paper uses the differentially amplified echo pulse signal to perform differential level shift and sends the shifted differential signal to the high-speed comparator for time discrimination, realizing the function of time discrimination. Through verification, the design can effectively improve the walking error caused by the front-line time identification method, which also improves the ranging accuracy. Compared with the constant ratio timing identification circuit, the circuit is simplified.

In order to improve the accuracy of flatness measurement, an optimized point laser method is proposed. Firstly, point laser measurement coordinate system is converted. Secondly, plan is calibrated with laser beam, and mixed noise points of laser acquisition are reduced using sliding filter to avoid affecting the test. Nonlinear error of measurement data and output model of laser displacement sensor are established to compensate the output error. Finally, the best fitting plane is obtained by least square algorithm. Experiment results show that the average flatness error of the optimized point laser is 5.189 μm, which is 18.77%, 16.78%, 12.45%, 9.17% and 6.54% lower than direct method, plane scanning, transverse scanning, point laser and spectral confocal, and the measurement accuracy is higher than other algorithms.

Combined with the principle of triangulation and the advantages of visual laser, aiming at the problem of terrain texture mapping, a 3D terrain texture mapping system based on multi-point structured light is designed. The system keeps the relative position of laser and camera fixed, which can collect depth information and texture information at the same time. After image processing, 3D virtual terrain with texture detail information can be generated, and the real-time performance of texture mapping results can be improved. The direction error of the system in depth measurement can be controlled within 1.3 mm. Due to the simple platform, no additional camera is required to collect texture information. Compared with the traditional three-dimensional measurement system, the cost is reduced, and the efficiency of modeling is improved.

Titanium clad steel plate has been widely used because of the excellent corrosion resistance of Ti and the low cost of constituent material, but the quality of the bonding surface directly affects its overall strength. Therefore, an effective nondestructive testing method is needed to detect the debonding. The use of non-contact ultrasonic techniques can have distinct advantages over conventional contact methods, allowing more rapid and practical scanning without suffering from variations introduced by an acoustic couplant. In this paper, a laser-electromagnetic ultrasonic detection method for debonding defects is proposed to evaluate the bonding performance. A linear light spot with a length of 10 mm and a width of 0.2 mm irradiates the material to produce spattering material. Longitudinal waves are generated in a sample by means of the splash recoil, and they are obscured by debonding defects. Thus, the amplitude of the signal received by the electromagnetic ultrasonic transducer (EMAT) with center frequency of 1 MHz at the opposite side is attenuated, and the amplitude decreases with the increase of occlusion length. Especially, when the amplitude attenuation is half of the reference value, the defect boundary is on the line between the spot center and the transducer center. According to the change law of signal amplitude, the defect boundaries and its area can be determined. Theoretical analysis and debonding measurement experiments show that the non-contact laser electromagnetic ultrasonic method can be used as an effective detection technology for debonding defects of titanium clad steel plate.

Defect inspection of small-diameter metal cylinders is a difficult problem in the field of nondestructive testing. In this paper, the propagation characteristics of shear wave in a cylinder and the interaction mechanism with defects were investigated by the finite element method. The directional change of the shear wave is explored by extracting the shear wave signals at different moments. The effect of the defect radius of the circular hole on the propagation of the shear wave was investigated by B-scan. The influence of different positions and different lengths of defects on the propagation of shear wave was investigated by C-scan. Results show that: the main energy range of shear wave in the propagation process changes from 15°-36° to 20°-35°. The propagation path of an approximate equilateral triangle is proposed and verified. For round hole defects of different radii, radius can be determined by the amplitude and receiving time changes. When the defects enter the main energy range of the shear wave, the detection angle increases with the increase of the defect position. The position information can be determined by the detection angle of the reflected signal. With the increase of defect length, the transmitted wave ST energy decreases and the detection angle decreases, presenting an approximately linear energy distribution. Defect length information can be determined by detecting the angle of the transmitted wave reaching the outer surface. The propagation path and length calculation formula are put forward, and the error percentage of the calculation result is controlled within 6.5%.

In order to analyze the mask material and establish the identification method of mask material evidence, 107 mask fiber samples were detected using Raman spectrometer for the study of the influence of black, pink and blue dyes on the Raman spectrum of mask fiber. Based on principal component analysis and correlation test, masks of different brands and batches of the same brand were distinguished, and the prediction of unknown brand mask was realized. The results show that under the condition of the same Raman characteristic peak, the mask with the strongest correlation with unknown brand can be quickly found by analyzing the difference of Raman intensity of mask fiber and the score chart of principal component. In the crime scene simulation experiment, the distance between unknown brand and similar brand is the closest in the principal component score graph, and the correlation coefficients of Pearson, Kendall rank and Spearman are the largest, which are 0.932, 0.799 and 0.942, respectively. Based on this, the mask with high similarity to unknown brand is found. This method reduces the scope of material evidence search, which can provide the basis for public security to find clues.

The surface of 316L stainless steel was melted by fiber laser. The effect of laser surface melting on the microstructure and wear resistance of 316L stainless steel was studied. Results show that a 500 μm thick layer with good metallurgical quality and free crack can be obtained on the surface of 316L stainless steel by laser surface melting. Compared with the original sample, the gradient refinement structure of equiaxed crystal, dendrite and columnar crystal is formed in the surface layer from top to bottom, the microhardness is increased by 73.9%, the friction coefficient is reduced by 37.8%, and the wear loss is reduced by 38.5%. The wear mechanism changes from abrasive wear and adhesive wear to slight abrasive wear, which indicates that the wear resistance of the substrate is significantly improved after laser surface melting treatment.

The CoCrFeNiMo/SiC high entropy alloy coating with SiC particles was prepared by laser cladding with 45Cr steel for internal combustion engine. The differences and influencing factors in microstructure, mechanical properties and wear resistance between the first CoCrFeNiMo (S1), the second CoCrFeNiMo and 10%SiC (S2), the third CoCrFeNiMo and 20%SiC (S3) were compared and analyzed. Results showed that in addition to FCC phase structure, M7C3 components (M stands for Cr, Mn, Fe) were detected in S2 and S3 samples. There is a circular arc structure between S1 coating and substrate. The longitudinal section of S2 coating forms a good bonding state. The second sublayer with smaller thickness was formed in S3 coating, and the coating dilution rate increased. After adding SiC into the sublayer, the brittle and hard M7C3 products were formed, which showed higher hardness. Obvious abrasive wear occurred after S1 coating wear. The surface area of S2 coating formed deeper wear marks and a large amount of shedding occurred. S3 coating formed more large size precipitates, which showed the characteristics of abrasive wear.

Aiming at problems such as low efficiency and over-segmentation in complex background segmentation, a 3D point cloud segmentation method based on normal estimation is proposed. First, the RANSAC algorithm is improved, and normal constraints are introduced to remove most of the plane point clouds in the background. As a result, the target point cloud is separated from a large number of point clouds. Then European clustering is used to extract the target point cloud from it. This paper uses the zokor skull point cloud data for experiments, and experimental results show that the merged point cloud segmentation algorithm can accurately segment the target Zokor Skull point cloud, completely remove the redundant point cloud, with fast speed, high accuracy, which shows better performance than the same type of method.

In the judicial practice of public security, seal paste is playing an important role in identifying the authenticity of documents for a long time. To provide evidence for determining the authenticity of the documents, a rapid nondestructive test was performed on 36 samples of inkpad using a SERDS Portable-Base portable differential Raman spectrometer under the test conditions of excitation source 785 nm, laser power 380 mW, scan time 10 s, and scan range 250~2 800 cm-1. The samples can be distinguished according to the position and number of characteristic peaks by analyzing the spectrum, and the samples in the same group can also be distinguished by the relative peak height ratio of characteristic peaks. At the same time, the principal component analysis method is used to reduce the dimension of the difference data, and the reduced dimension component matrix is systematically clustered. All the samples are scientifically divided into 7 categories, and the DP value is 85.23%. At the same time, a classification model based on cluster analysis is established by discriminant analysis. After cross validation, the classification accuracy is 94.4%. This method is fast, nondestructive, sensitive and strong anti fluorescence interference. Combined with the established model, it can scientifically test the inkpad samples, which can provide help for the front-line document inspection of public security.

In order to speed up the scabbing speed of sports micro-injury and promote the recovery and self-healing effect of sports micro-injury, a low-power laser repair system for the next sports micro-injury with hormone intervention was proposed. By analyzing the role of low-power laser in sports medicine, CMOS camera, sensor and light source are used as the hardware of the repair system, and the image output signal is obtained by driving pulse interference transmission. Different lighting methods are used to filter the image information, and the system software is composed of user interface, damage detection module, laser module, main control module, vision module and configuration module. Relying on this system, the excessive production of collagen fibers, active oxygen production, lipid peroxidation damage and muscle regeneration are inhibited.Experimental results show that the low-power laser repair system under the interference of hormone can effectively repair different degrees of sports micro-injuries, and make the scarring speed of damaged areas faster.

In response to the requirements of the working environment in various complex spaces in the cabin, laser cleaning technology is used to carry out process test research on the paint, rust and oil pollution on the surface of marine steel EH36. First, the effects of the combination of laser power, repetition frequency, and pulse width process parameters on the surface morphology are studied, and the effects of different parameters on the degree of surface peeling and roughness are revealed. At the same time, it is necessary to avoid surface cracks. A single factor test is designed to obtain the best cleaning process window for paint, rust and oil stains. Paint and oil stains can be removed by a laser scan, and rust needs to be cleaned twice. By comparing the surface element content distribution and microscopic morphology changes of the substrate before and after cleaning, results show that the elements C, N, and O related to surface contaminants after laser cleaning are greatly reduced, rust and oil stains can be completely removed, and the paint layer exists A small amount of small flakes remain. Finally, the mechanical properties of the cleaned substrate were tested, and it was found that the hardness of the surface layer was improved. The rust removal sample increased by about 20 HV, the oil removal sample increased by about 3 HV, and the paint removal sample increased by about 13 HV. The tensile and bending properties of the material have no obvious influence. Therefore, the laser cleaning process of marine steel is reliable and non-destructive.

Objective To systematically review the efficacy and safety of percutaneous laser disc decompression (PLDD) combined with ozone injection in the treatment of lumbar disc herniation(LDH). Methods We searched PubMed, Embase, the Chochrane library, Web of Science, CBM, Wanfang Data, VIP and CNKI databases, Randomized controlled trials (RCTs) on the efficacy and safety of PLDD combined with ozone injection in the treatment of LDH were collected, and the retrieval time is from the establishment date to March 1, 2021. The two researchers independently conducted literature retrieval, screening, data extraction, literature quality and risk of bias evaluation. Meta-analysis was conducted by using RevMan 5.3 software. Results Eighteen RCTs, including 3069 patients, were eventually included. Meta-analysis results showed that: compared with use PLDD or ozone injection individually in the treatment of LDH, PLDD combined with ozone injection can significantly increase the curative effect of modified MacNab evaluation standard ［the OR=3.76, 95% CI (2.89, 4.90), P<0.000 01), reduce the Visual Analogue Scales (VAS) ［MD=-0.85，95%CI（-1.32，-0.38），P=0.0004］, improve the excellent rate of Japanese Orthopaedic Association scores, (JOA) ［OR=4.28, 95% CI (3.39, 5.41), P < 0.000 01］, the difference was statistically significant. Conclusion the existing evidence showed that, compared with the PLDD or ozone injection be used alone in the treatment of LDH，PLDD combined with ozone injection, as a kind of interventional therapy in the treatment of LDH, can improve the curative effect of modified Macnab evaluation standard, the excellent rate of Japanese Orthopaedic Association scores(JOA), reduce the Visual Analogue Scales (VAS), high security. Owing to the limitation of the quantity and quality of the included studies, the above conclusions need to be further verified by a large number of multi-center, large-sample and high-quality studies.