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Finite Element Analysis of Surface Roughness Generated by Multiple Laser Shock Peening
摘要： Laser shock peening (LSP) is a novel surface processing technique for improving the fatigue properties of metal parts, and surface roughness is a critical parameter when fatigue strength resistance is concerned. In this paper, a three-dimensional (3D) finite element model was developed in order to assess the surface roughness evolution induced by multiple LSP. A modified finite element analysis (FEA) method was used to compute the vertical displacements profiles, and discrete data obtained from the numerical simulations were subsequently input to the proposed discretized formula to calculate the surface roughness Ra. The results obtained from the numerical simulations are in good agreement with the experiment data from open literatures, which validates the proposed approach. After the validation of the numerical model, a parametric study was conducted in order to predict the effects of overlap rates, number of impacts, and pulse energy on surface roughness Ra.
关键词： laser shock peening,surface roughness Ra,numerical simulation
更新于2025-09-16 10:30:52
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Investigation of the effects of nonstationary features on rock joint roughness using the laser scanning technique
摘要： Accurately estimating rock joint roughness is crucial for understanding the shear mechanism and permeability behavior of a rock mass. Several influencing factors, including anisotropy, measurement noise, and the scale effect and sampling interval, have been considered. However, little attention is paid to the influences of nonstationary features on the roughness assessment. In this study, a portable laser scanner was employed to collect high-density 3D point clouds of ten natural rock joint specimens. Based on two parameters, namely, the bright area percentage (BAP) and θ*max/(C + 1), where θ*max is the maximum apparent dip angle and C is a dimensionless fitting parameter, the rock joint roughness was determined before and after removing nonstationary features, and a comparison showed that nonstationary features have a considerable influence on the roughness. Subsequently, an approach was proposed to remove nonstationary features through the conversion of spatial coordinates, and an application to a roughness evaluation illustrated that similar trends are observed between the BAP and θ*max/(C + 1) with respect to the point clouds of ten rock joints whose nonstationary features were removed. These findings reveal that nonstationary features should be removed to improve the accuracy and comparability of the roughness assessments.
关键词： 3D laser scanning,Rock joint,Roughness estimation,Nonstationary features
更新于2025-09-16 10:30:52
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New Method for Evaluating Surface Roughness Parameters Acquired by Laser Scanning
摘要： Quality evaluation of a material’s surface is performed through roughness analysis of surface samples. Several techniques have been presented to achieve this goal, including geometrical analysis and surface roughness analysis. Geometric analysis allows a visual and subjective evaluation of roughness (a qualitative assessment), whereas computation of the roughness parameters is a quantitative assessment and allows a standardized analysis of the surfaces. In civil engineering, the process is performed with mechanical profilometer equipment (2D) without adequate accuracy and laser profilometer (3D) with no consensus on how to interpret the result quantitatively. This work proposes a new method to evaluate surface roughness, starting from the generation of a visual surface roughness signature, which is calculated through the roughness parameters computed in hierarchically organized regions. The evaluation tools presented in this new method provide a local and more accurate evaluation of the computed coefficients. In the tests performed it was possible to quantitatively analyze roughness differences between ceramic blocks and to find that a quantitative microscale analysis allows to identify the largest variation of roughness parameters Raavg, Rasdv, Ramin and Ramax between samples, which benefit the evaluation and comparison of the sampled surfaces.
关键词： roughness parameters,laser scanning,hierarchical analysis,civil engineering,surface roughness
更新于2025-09-12 10:27:22
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Impulse Laser Effect on Graphitized Surface of Y–TZP-Ceramics
摘要： The role of a graphite layer on the surface of ceramics based on tetragonal zirconia, partially stabilized by yttrium oxide (Y–TZP-ceramics) under the action of a pulsed laser was studied using original methodology. It has been found that surface graphitization increases the fraction of absorbed laser radiation, and as a result, heating, melting and evaporation of Y–TZP-ceramics occur under less intense modes, favorably affecting the use of pulsed laser radiation for surface modification.
关键词： Y–TZP-ceramics,graphite layer,pulsed laser effect,surface layer,roughness,surface morphology
更新于2025-09-12 10:27:22
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Systematic approach for determining optimal processing parameters to produce parts with high density in selective laser melting process
摘要： Relying on trial-and-error methods to determine the optimal processing parameters which maximize the density of parts produced using selective laser melting (SLM) technique is costly and time consuming. With a given SLM machine characteristics (e.g., laser power, scanning speed, laser spot size, and laser type), powder material, and powder size distribution, the present study proposes a more systematic strategy to reduce the time and cost in finding optimal parameters for producing high-density components. In the proposed approach, a circle packing design algorithm is employed to identify 48 representative combinations of the laser scanning speed and laser power for a commercial Nd:YAG SLM system. For each parameter combination, finite element heat transfer simulations are performed to calculate the melt pool dimensions and peak temperature for 316L stainless steel powder deposited on a 316L substrate. The simulated results are then used to train the artificial neural networks (ANNs). The trained ANNs are used to predict the melt pool dimensions and peak temperature for 3600 combinations of the laser power and laser speed in the design space. The resulting processing maps are then inspected to determine the particular parameter combinations which produce stable single scan tracks with good adhesion to the substrate and a peak temperature lower than the evaporation point of the SS 316L powder bed. Finally, the surface roughness measurements are employed to confirm the parameter settings which maximize the SLM component density. The experimental results show that the proposed approach results in a maximum component density of 99.97 %, an average component density of 99.89%, and a maximum standard deviation of 0.03%.
关键词： Additive manufacturing,Selective laser melting,Surface roughness,Artificial neural network,Surrogate model
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Achievement of Very Smooth Cavity Sidewalls by UV Picosecond Laser Micromachining
摘要： Achievement of very smooth cavity sidewalls by UV picosecond laser micromachining. As a contactless and maskless method generating a reduced heat affected zone compared to nanosecond laser, ultrafast laser micromachining is widely used for rapid prototyping and materials processing. Today, most research and development works is devoted to study and control LIPPS occurring at the surface of the cavity bottom. But for many applications, there is a strong need to produce highly smooth sidewalls like for microelectronic sample preparation, microfluidics, waveguides, etc.. A laser based technology allowing to obtain very smooth surfaces (Ra of ~3 nm) already exists but it involves melting of a significant volume of material. So far, to the best of our knowledge, no parametric study aiming at minimizing the roughness of picosecond laser micromachined sidewalls in silicon has been performed. In the present work, picosecond laser micromachining (532 nm and 343 nm) of cavity sidewalls in silicon is studied. The evolution of the surface roughness is deeply investigated experimentally and theoretically as a function of laser and scanning parameters. We demonstrate that RaX, which is measured along the scanning laser beam direction, can be minimized by increasing laser beam overlap and the crater size, in accordance with a simple geometrical model. Experimentally, the minimum RaX is obtained for a beam overlap of ~80% and the largest crater sizes. Beyond 80%, we observed a roughness degradation which is probably due to two main phenomena. The first involves the interaction between the laser beam and the debris, which deteriorates the beam quality. The second is related to the highly heterogeneous ablation occurring for large overlaps, which induces a rough surface. Along the beam propagation direction, the sidewall is characterized by a relatively high waviness which induces a more important height variation than the roughness. The waviness depends mainly on the Rayleigh length. Thus, it can be reduced by using a large focal spot radius and a short wavelength. Once the sidewall is finished, the surface topology does not vary much with the laser micromachining time. Overall, smooth and homogeneous surfaces can be produced by choosing a beam overlap close to 80%. The best results were obtained at 343 nm, which allows to extend the Rayleigh zone, to increase the laser absorption on the sidewall asperities and to improve the induced cleaning thanks to a more confined interaction. The present work demonstrates that very low roughness (< 40 nm) can be achieved on sidewalls of cavities by picosecond laser micromachining. In addition this approach allows the roughness tuning. As it is based on a geometrical model, it is extendable to other materials as long as the surface melting, which may erase the induced periodic structuring, is not significant. This tuning possibility can be useful to modify the surface properties, such as reflectivity, friction and wettability, and therefore adapt the sidewall to different applications.
关键词： smooth cavity sidewalls,waviness,silicon,UV picosecond laser,roughness,micromachining,Rayleigh length
更新于2025-09-12 10:27:22
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Improvement of CsPbBr3 photodetector performance by tuning the morphology with PMMA additive
摘要： The optoelectrical properties of semiconductor devices are strongly related to the film morphology. Here, we found that, for CsPbBr3 thin films prepared by spray coating, the addition of polymethyl methacrylate (PMMA) can completely eliminate voids and greatly reduce the surface roughness of the as-deposited films. As a consequence, the optoelectronic properties of the photodetectors fabricated as a simple vertical structure of Au/CsPbBr3(PMMA)/ITO can be improved. With the addition of PMMA, the dark current of the photodetector is reduced at least four times, and the photodetector exhibits a favourable optical response. With the illumination ranging from 400 to 510 nm, the calculated responsivity varies from 3.70 to 5.20 A/W. A good response speed with a rise time of 6.6 ms and a decay time of 11.3 ms can be achieved. Moreover, unlike the inorganic-organic hybrid perovskite detectors, this inorganic perovskite photodetector without encapsulation shows a favourable stability with a decay of 20% after 40 days under ambient air at 20% humidity.
关键词： Photodetector,Spray coating,PMMA,Surface roughness,CsPbBr3
更新于2025-09-12 10:27:22
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Effect of repeated laser surface treatments on shear bond strength between zirconia and veneering ceramic
摘要： Statement of problem. Delamination failure may occur between ceramic frameworks and veneering ceramics, shortening the lifetime of ?xed dental prostheses in load-bearing areas. Purpose. The purpose of this in vitro study was to compare the effect of different repeating CO2 laser treatment methods and conventional approaches on the shear bond strength of zirconia frameworks and veneering ceramics. Material and methods. Zirconia disks (N=110) were prepared and divided into 5 groups: milling without surface treatment (group M), airborne-particle abrasion (group APA), single laser treatment (group LX1), 2 laser treatments (group LX2), and 3 laser treatments (group LX3). The specimens in the ?rst 2 groups were treated before the framework was coated using the spraying technique. Specimens in the remaining groups were coated with veneering ceramic using the spraying process, and then subjected to laser treatment. Surface roughness and topography, interface properties, phase transformation, shear bond strength, and fracture modes were investigated. Outcomes were analyzed using a pro?lometer, a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD), a stereomicroscope, and a universal testing machine for mechanical testing. Results. The XRD showed that phase transformation from tetragonal to monoclinic occurred after airborne-particle abrasion. This phenomenon was not observed in laser-treated specimens. Groups LX2 and LX3 had the highest surface roughness values, 1.18 ±0.23 mm and 1.21 ±0.22 mm, among all groups, and group LX3 had the highest shear bond strength values for unaged and aged conditions, 32.08 ±2.45 MPa and 31.43 ±2.07 MPa. The mixed-fracture mode was the most common type of fracture observed. Conclusions. The results indicated that the shear bond strength between the zirconia framework and veneering ceramic was higher after laser surface treatments than after milling alone or after airborne-particle abrasion. Laser treatment methods, particularly LX2 and LX3, could be considered reliable approaches for zirconia surface treatment.
关键词： veneering ceramic,laser treatment,zirconia,shear bond strength,surface roughness
更新于2025-09-12 10:27:22
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Melt pool monitoring for laser beam melting of metals: inline-evaluation and remelting of surfaces
摘要： Laser Beam Melting of Metals (LBM-M) is an additive manufacturing technique that is applied successfully for the production of complex parts, small batch series and prototypes. In LBM metallic parts are generated layer by layer directly from sliced CAD data. For each layer a thin powder layer is deposited and subsequently irradiated by a focused laser beam which is guided by a galvanometer scanner. Due to variations in the powder stock, plain parameter sets and unresolved machine maturity problems, quality fluctuations are a major problem for a future series production. Surface roughness of parts during manufacturing is a quality issue. In this paper, we address it with a coaxial melt pool monitoring system and show a method for inline evaluation of surfaces by means of melt pool monitoring and the results of applied remelting strategies.
关键词： Laser Beam Melting,Additive Manufacturing,process stability,remelting,Selective Laser Melting,Melt pool Monitoring,Surface roughness,quality assurance
更新于2025-09-12 10:27:22
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Study of correlation between edge roughness and gas flow characteristics in laser beam fusion cutting
摘要： Fiber laser fusion cutting trials on AISI 304 stainless steel sheets of 10 mm thickness were performed with the aim to gain further insights into the striation formation process on cut edges. The study is based on a factorial Design-of-Experiment (DoE) approach with consideration of laser power, focal plane position, gas pressure, nozzle stand-off and nozzle diameter as control factors. Analyzed responses include the achievable cutting speed, the cut kerf geometry and the cut edge roughness. In addition, numerical simulations of the cutting gas flow were carried out for adapted kerf geometries and gas parameters. The evaluation of these results reveals strong correlations between experimental roughness values and the numerically computed rear-directed shear stress component within the transition zone between cutting front and cut edge surface. This finding supports the hypothesis that the particular characteristics of the boundary layer zone of the cutting gas flow affects the structure and roughness of cut edges.
关键词： Laser beam fusion cutting,edge roughness,modelling and simulation,gas flow characteristics,design-of-experiments
更新于2025-09-12 10:27:22