Surface Topography Data Research Articles

Topography stitching in the spatial frequency domain for the representation of mid-spatial frequency errors.

Sub-aperture fabrication techniques such as diamond turning, ion beam figuring, and bonnet polishing are indispensable tools in today's optical fabrication chain. Each of these tools addresses different figure and roughness imperfections corresponding to a broad spatial frequency range. Their individual effects, however, cannot be regarded as completely independent from each other due to the concurrent formation of form and finish errors, particularly in the mid-spatial frequency (MSF) region. Deterministic Zernike polynomials and statistical power spectral density (PSD) functions are often used to represent form and finish errors, respectively. Typically, both types of surface errors are treated separately when their impact on optical performance is considered: (i) wave aberrations caused by figure errors and (ii) stray light resulting from surface roughness. To fill the gap between deterministic and statistical descriptions, a generalized surface description is of great importance for bringing versatility to the entire optical fabrication chain by enabling easy and quick exchange of surface topography data between three disciplines: optical design, manufacturing, and characterization. In this work, we present a surface description by stitching the amplitude and unwrapped phase spectra of several surface topography measurements at different magnifications. An alternative representation of surface errors at different regimes is proposed, allowing us to bridge the gap between figure and finish as well as to describe the well-known MSF errors.

Experimental Investigation on Al 6061 and Al 2024 Aluminium alloys for achieving Surface Roughness using CNC Vertical Face Milling Process

Abstract: The influence of process factors and the integrity of the surface roughness are investigated experimentally in the current study on the metals Al6061 and Al2024. In order to conduct vertical cutting tests for both base alloys, a mixed level L9 orthogonal array is used. An optical emission spectrometer is used to analyse the chemical composition. SEM is used to analyse the microstructure of the materials used to discover tiny inertinitic precipitates in an aluminum matrix using ANOVA Table value. Mild steel was the tool employed, and surface topography and 2D roughness profile data were used to assess the surface integrity of cut surfaces. The experimental trials with various degrees of process parameters, such as Taguchi L9 orthogonal array. In determining surface roughness, speed, feed, and depth of cut are determined to be the most important variables.

Thresholding Methods for Reduction in Data Processing Errors in the Laser-Textured Surface Topography Measurements.

There are many factors influencing the accuracy of surface topography measurement results: one of them is the vibrations caused by the high-frequency noise occurrence. It is extremely difficult to extract results defined as noise from the real measured data, especially the application of various methods requiring skilled users and, additionally, the improper use of software may cause errors in the data processing. Accordingly, various thresholding methods for the minimization of errors in the raw surface topography data processing were proposed and compared with commonly used (available in the commercial software) techniques. Applied procedures were used for the minimization of errors in the surface topography parameters (from ISO 25178 standard) calculation after the removal and reduction, respectively, of the high-frequency noise (S-filter). Methods were applied for analysis of the laser-textured surfaces with a comparison of many regular methods, proposed previously in the commercial measuring equipment. It was found that the application of commonly used algorithms can be suitable for the processing of the measured data when selected procedures are provided. Moreover, errors in both the measurement process and the data processing can be reduced when thresholding methods support regular algorithms and procedures. From applied, commonly used methods (regular Gaussian regression filter, robust Gaussian regression filter, spline filter and fast Fourier transform filter), the most encouraging results were obtained for high-frequency noise reduction in laser-textured details when the fast Fourier transform filter was supported by a thresholding approach.

Surface topography data fusion of additive manufacturing based on confocal and focus variation microscopy.

In this paper, two innovative data fusion methods are proposed for reconstructing the surfaces produced by directed energy deposition (DED) additive manufacturing. The surface topographic data were obtained from confocal laser scanning microscopy (CLSM) and focus variation microscopy (FV). The first method (competitive data fusion) aims to improve the data quality by combining both the advantages of the CLSM and FV techniques, while the second method (cooperative data integration) is designed for generating a single representation that contains not only global information but also local details. The results show that both fusion methods achieved satisfactory results: in the competitive fusion, the fused data preserved the characteristics of FV data while its vertical resolution is also improved by integrating the short waves from the CLSM data; the cooperative data fusion achieved one pixel precision of the surface registration which adopted the feature-based registration method with the help of color image information. The computational complexity is reduced from O((m×n)2) to O(m×n + k). Both proposed data fusion methods provided innovative solutions for the microscopic surface reconstruction and surface representation in multiscales in the field of additive manufacturing.

Effect of overhanging surfaces on the evolution of substrate topography and internal defects formation in laser powder bed fusion

Overhanging (a.k.a. down-facing) surfaces are typically found in complex metal parts built with laser powder bed fusion (L-PBF). When these surfaces exceed a certain extension or inclination with respect to the build plate, they need to be supported with external structures to avoid failure and macro-geometrical errors. However, a relatively large portion of the slice gets printed directly over loose powder, thus facing a substrate with significantly different wetting and heat transfer characteristics from solid/bulk. Several quality aspects (e.g., internal defects, surface topography) can be affected by the presence of overhangs, but their evolution during the process is still a relatively unexplored field. In this work, a new strategy based on process interruption is proposed for analyzing the evolution of defects produced during the printing of down-facing surfaces. Ex-situ high-accuracy characterization equipment was used to study their effect on the evolution of printed surface topography, internal defects, melted and sintered thickness. Results show that the process gradually recovers from the disturbance introduced by the overhang, but the peculiar structure of the internal defects observed in those regions reveals that even small unsupported areas can be detrimental to the as-built quality of the part. The combined use of surface topography data and volume reconstruction also allowed developing and validating a physics-based model for predicting the evolution of surface topography and effective layer thickness in overhangs.

Research on Micro/Nano Surface Flatness Evaluation Method Based on Improved Particle Swarm Optimization Algorithm.

Flatness error is an important factor for effective evaluation of surface quality. The existing flatness error evaluation methods mainly evaluate the flatness error of a small number of data points on the micro scale surface measured by CMM, which cannot complete the flatness error evaluation of three-dimensional point cloud data on the micro/nano surface. To meet the needs of nano scale micro/nano surface flatness error evaluation, a minimum zone method on the basis of improved particle swarm optimization (PSO) algorithm is proposed. This method combines the principle of minimum zone method and hierarchical clustering method, improves the standard PSO algorithm, and can evaluate the flatness error of nano scale micro/nano surface image data point cloud scanned by atomic force microscope. The influence of the area size of micro/nano surface topography data on the flatness error evaluation results is analyzed. The flatness evaluation results and measurement uncertainty of minimum region method, standard least squares method, and standard PSO algorithm on the basis of the improved PSO algorithm are compared. Experiments show that the algorithm can stably evaluate the flatness error of micro/nano surface topography point cloud data, and the evaluation result of flatness error is more reliable and accurate than standard least squares method and standard PSO algorithm.

Correlation between Fractal Dimension and Areal Surface Parameters for Fracture Analysis after Bending-Torsion Fatigue

This paper investigates the fracture surface topography of two steel and aluminum alloys subject to bending-torsion fatigue loadings, as well as their susceptibility to fatigue performance and failure mechanisms. Using fracture surface topography data analysis, elements with different geometries were elaborated. A correlation between the fractal dimension, other selected parameters of surface topography such as areal Sx, and fatigue loading conditions was found. Distinctions in particular regions of cracks were also recognized through proving the correctness and universality of the total fracture surface method. The influence of fatigue loading parameters on the surface topography of fatigue fractures was demonstrated. For the analyzed cases, results show that the fractal dimension and standard surface topography parameters represent a correlation between them and loading conditions. As a single parameter, the appropriate loading ratio cannot be outright calculated with fractal dimension, but can be estimated with some approximation, taking into account additional assumptions.

Modeling and Analysis of Micro Surface Topography from Ball-End Milling in a Trochoidal Milling Mode.

The trochoidal milling mode is widely used in high-speed machining, and due to good adaptability and flexible posture adjustment, ball-end milling cutters are conducive to complex surface machining with this mode. However, the processes of material removal and formation of machined micro surfaces are very difficult to describe as the profile of cutter teeth is complex and the trajectory direction changes continuously during the trochoidal milling process. A modeling method for the generation of micro surface topography of ball-end milling in the trochoidal milling mode is put forward. In this method, the locus equation of each cutter tooth is established based on the principle of homogeneous coordinate transformation, after which a Z-MAP algorithm is designed to simulate the micro surface topography. The Z-MAP algorithm can quickly obtain the part grid nodes potentially swept by the cutter tooth within a unit time step through the establishment of servo rectangular encirclement and instantaneous sweeping quadrilateral of the element of cutter teeth; the part grid nodes actually swept are further determined through an angle summation method, and the height coordinate is calculated with the method of linear interpolation according to Taylor’s formula of multivariate functions. Experiments showed that the micro surface topography resulting from ball-end milling in the trochoidal milling mode had high consistency with the simulation, which indicates that the proposed method can predict micro surface topography in practical manufacturing. In addition, a comparison of micro surface topography between trochoidal milling and ordinary straight-linear milling was conducted, and the results showed that the former was overall superior to the latter in resulting characteristics. Based on this conclusion, the influences of cutting parameters of ball-end trochoidal milling on surface characteristics, particularly amplitude and function, were analyzed according to the simulated micro surface topography data.

Similarity quantification of 3D surface topography measurements

3D surface topography provides critical information about surface textures and has begun to be used in additive manufacturing applications such as in-situ 3D monitoring and sample porosity comparisons, etc. In this research, we establish a thorough framework to quantify the similarity of 3D surface topography measurements and determine whether they are from the same surface or not based on the frequency domain representations after 2D Fourier transformation. Two measurements portraying the same surface are defined as a matched pair while the others are unmatched. This framework quantifies the similarity effectively, provides a new perspective for surface topography similarity evaluation, and serves as a benchmark work in 3D surface topography feature extraction in the frequency domain. Our work has a great potential to benefit not only the quality assurance of AM but also many other communities where surface topography data is useful.

Suppression of the High-Frequency Errors in Surface Topography Measurements Based on Comparison of Various Spline Filtering Methods.

The metrology of so-called “engineering surfaces” is burdened with a substantial risk of both measurement and data analysis errors. One of the most encouraging issues is the definition of frequency-defined measurement errors. This paper proposes a new method for the suppression and reduction of high-frequency measurement errors from the surface topography data. This technique is based on comparisons of alternative types of noise detection procedures with the examination of profile (2D) or surface (3D) details for both measured and modelled surface topography data. In this paper, the results of applying various spline filters used for suppressions of measurement noise were compared with regard to several kinds of surface textures. For the purpose of the article, the influence of proposed approaches on the values of surface topography parameters (from ISO 25178 for areal and ISO 4287 for profile standards) was also performed. The effect of the distribution of some features of surface texture on the results of suppressions of high-frequency measurement noise was also closely studied. Therefore, the surface topography analysis with Power Spectral Density, Autocorrelation Function, and novel approaches based on the spline modifications or studies of the shape of an Autocorrelation Function was presented.

Similarity evaluation of 3D surface topography measurements

With the recent advances in three-dimensional (3D) optical scanning technologies, 3D surface topography measurement plays an increasingly important role in many fields, such as product quality inspection in additive manufacturing (AM), gauge capability analysis, and firearm identification in forensic science. In this paper, we establish a thorough and flexible new framework of surface topography data comparison that generates a scaled similarity score for a pair of measurements, and distinguishes matched and non-matched pairs based on the score. If two measurements are portraying the same surface, they are defined as a matched pair. If not, they are defined as a non-matched pair. This similarity evaluation framework can be very useful in comparing optical scanning systems, quantifying different sources of variation in a process, and monitoring the stability and uniformity of a process, thus has a great potential to improve the quality assurance cycle of AM processes in the long run. We illustrate the framework and statistically evaluate the binary classification performance on data measured from additive manufactured parts on a large scale. We also examine how different systems, repeated measurements, and operators affect the similarity score and classification performance. We compare our work with a baseline method using the surface roughness average parameter Ra. The results show that the methodology can distinguish matched and non-matched pairs with high accuracy, and it outperforms the baseline method greatly. The framework serves as a benchmark method and can be generalized to be used in other fields where surface topography plays a critical role.

Surface Mass-Balance Gradients From Elevation and Ice Flux Data in the Columbia Basin, Canada

The mass-balance—elevation relation for a given glacier is required for many numerical models of ice flow. Direct measurements of this relation using remotely-sensed methods are complicated by ice dynamics, so observations are currently limited to glaciers where surface mass-balance measurements are routinely made. We test the viability of using the continuity equation to estimate annual surface mass balance between flux-gates in the absence of in situ measurements, on five glaciers in the Columbia Mountains of British Columbia, Canada. Repeat airborne laser scanning surveys of glacier surface elevation, ice penetrating radar surveys and publicly available maps of ice thickness are used to estimate changes in surface elevation and ice flux. We evaluate this approach by comparing modeled to observed mass balance. Modeled mass-balance gradients well-approximate those obtained from direct measurement of surface mass balance, with a mean difference of +6.6 ± 4%. Regressing modeled mass balance, equilibrium line altitudes are on average 15 m higher than satellite-observations of the transient snow line. Estimates of mass balance over flux bins compare less favorably than the gradients. Average mean error (+0.03 ± 0.07 m w.e.) between observed and modeled mass balance over flux bins is relatively small, yet mean absolute error (0.55 ± 0.18 m w.e.) and average modeled mass-balance uncertainty (0.57 m w.e.) are large. Mass conservation, assessed with glaciological data, is respected (when estimates are within 1σ uncertainties) for 84% of flux bins representing 86% of total glacier area. Uncertainty on ice velocity, especially for areas where surface velocity is low (<10 m a−1) contributes the greatest error in estimating ice flux. We find that using modeled ice thicknesses yields comparable modeled mass-balance gradients relative to using observations of ice thickness, but we caution against over-interpreting individual flux-bin mass balances due to large mass-balance residuals. Given the performance of modeled ice thickness and the increasing availability of ice velocity and surface topography data, we suggest that similar efforts to produce mass-balance gradients using modern high-resolution datasets are feasible on larger scales.

Evaluation of polishing-induced subsurface damage based on residual stress distribution via measured global surface deformation for thinned silicon wafers

Polishing is widely used to obtain smooth thinned wafer surfaces and the process-induced subsurface damage is often evaluated by scanning electron microscope or transmission electron microscope images. However, the difference of microscope images is very slight and subtle between wafers and affected by the location selection of the measured points. In this study, we explored the method of evaluating the polishing-induced subsurface damage based on residual stress distribution via measured global surface deformation. The surface deformation was first measured and then the polishing-induced residual stress distribution was calculated from the surface topography data by solving the system of linear equations. The polishing-induced subsurface damage could be evaluated independent of the dimension of the silicon wafer by the proposed method. How the thinned silicon wafer was supported during measurement process greatly affected polishing-induced wafer deformation and gravity-induced deformation should be separated from the measured data. Regularization method should be introduced in the calculation of residual stress to reduce the errors caused by the multi-collinearity of the system of linear equations. The calculated residual stress distribution was found to be an obvious centrosymmetric figure and exhibited a quasi-axisymmetric pattern with the axis of symmetry correlated with certain crystalline directions, indicating the effect of anisotropy of monocrystalline silicon in the polishing process. The proposed method could also be used in the evaluation of polishing-induced subsurface damage of other large and thin substrate plates.

Sliding State Analysis of Fractal Rough Interface Based on the Finite Element Method.

Local high temperature, stress concentration, and abnormal friction coefficients will appear at the friction pair in a wet clutch as a result of surface topography real-time changing. In order to improve the reliability of clutch friction components and reduce the failure phenomenon, the three-dimensional fractal surface topography data of the actual rough surface asperities are scanned, extracted, and processed successively, and then the finite element model of the rotary sliding friction pair is established considering the micro surface topography. Based on the finite element model, the variation of surface stress and strain is analyzed, and the friction coefficient measured experimentally is taken as the model input. It is concluded that when the rough surface and smooth surface make contact with each other, the maximum stress and plastic strain appear at the inner radius edge. Therefore, this research has a guiding significance for the structural design and processing technology of the friction components in a vehicle clutch.

The Application of 3D Laser Scanning and Unmanned Ship Sounding in the Reexamination of Reservoir Storage Capacity

In order to accurately measure the reservoir capacity after siltation, this paper uses the ground 3D laser scanning system to obtain the topography above the water surface and the unmanned ship sounding system to obtain the topography below the water surface. then carry out the accurate review of the reservoir capacity through the combination model of water and underwater. The blind area of measurement is caused by the change of water level and detection conditions, which leads to measurement error. combined with the measured data of surface and underwater topography, the complete reservoir water level-area curve is obtained by water level-area fitting and contour interpolation fitting respectively, the error caused by blind area is minimized, and finally the reservoir capacity review is carried out according to the contour volume method. Practice has proved that the use of contour interpolation fitting method can greatly improve the credibility of the reservoir capacity review results, provide accurate and reliable basic data for reservoir management units, and provide support for reservoir flood control and operation.

Application of Gradient-based Edge Detection on Defined Surface Feature Boundary

In surface topography, the detection of edges or surface feature boundary should be made prior to the characterization process to ensure precise measurement of the surface feature. However, problem arises when the existing edge detection from the image processing area is being directly adopted on the surface without firstly defining the exact location of edges. Thus, an approach has been carried out with the aim of developing the definition of edges to identify its exact location. The process of developing the definition of edges is conducted based on theoretical understanding and demonstration on the simulated surface topography data with the help of MATLAB software. Gradient-based edge detection operators are applied to see their performance on the defined surface feature boundary. Overall findings of this study showed that there are slight discrepancies of the edge position signified by the gradient-based operators to manually-defined edges. Despite of such outcome, it is then recommended to use either the Sobel operator or the Prewitt operator as a tool to signify the edge before proceeding with characterization process in future study due to their stability and clarity in producing the surface gradient function.

Simulation and experiment on surface topography of complex surface in single point diamond turning based on determined tool path

Surface topography is an important element that reflects the machining quality of workpieces and the functional performance of components. To avoid expensive cutting experiments, forecasting the surface topography before actual machining is necessary. Surface topography of diamond turned surfaces is directly affected by generated tool path in ultraprecision single point diamond turning (SPDT). In this study, a novel surface topography modeling method was presented. The planned tool path based on active machining precision control was considered in this method. Simulation and experiment of an umbrella surface diamond turning were conducted to testify the usability of the proposed model. Through comparing the simulation and experimental data of surface topography and machining error, the results showed that the proposed model can be applied to forecast the surface topography and machining error in SPDT using the generated tool path.

Classification and Digital Mapping of Soils in a Semiarid Region of Afghanistan

A soil map provides information on soil spatial distribution. Such information is essential for effective use of soil resources for crop production, land evaluation, spatial planning, environmental control, and for other similar purposes. In this study, a digital soil map for a semiarid region of Afghanistan was developed. This map contains soil taxonomic information up to the subgroup level, which is the first such attempt in Afghanistan. A total of 114 soil samples were collected in and around the Khost Province through an intensive soil survey. The collected samples were classified into 14 subgroups of soils, following the USDA soil classification system. A soil land inference model (SoLIM) was applied for mapping the recognized 14 soil subgroups digitally, via an expert knowledge-based fuzzy soil inference scheme, with surface topography and other spatial data as inputs. The overall accuracies from the error matrix and Kappa statistics were 0.74 and 0.71, respectively. This map was also compared with the currently used soil map. A general agreement between the two maps was found in the spatial distribution of soil classes, at the great group level. However, the newly developed map contains more detailed information on soils, which might be useful for the advanced use of soil information, for example, to better determine the crop type for cultivation by considering the detailed soil properties. Throughout this study, 14 different recognized classes of soil subgroups were digitally mapped in the study area.

Precision Medicine in Ossiculoplasty.

Long term results of ossiculoplasty surgery are considered poor with displacement and extrusion amongst the common reasons for failure. Application of 3Dimensional (3D) printing may help overcome some of these barriers, however digital methods to attain accurate 3D morphological studies of ossicular anatomy are lacking, exacerbated by the limitation of resolution of clinical imaging. 20 human cadaveric temporal bones were assessed using micro computed tomography (CT) imaging to demonstrate the lowest resolution required for accurate 3D reconstruction. The bones were then scanned using conebeam CT (125 μm) and helical CT (0.6 mm). 3D reconstruction using clinical imaging techniques with microCT imaging (40 μm resolution) as a reference was assessed. The incus was chosen as the focus of study. Two different methods of 3D printing techniques were assessed. A minimum resolution of 100 μm was needed for adequate 3D reconstruction of the ossicular chain. Conebeam CT gave the most accurate data on 3D analysis, producing the smallest mean variation in surface topography data relative to microCT (mean difference 0.037 mm, p < 0.001). Though the incus varied in shape in between people, paired matches were identical. Thus, the contralateral side can be used for 3D printing source data if the ipsilateral incus is missing. Laser based 3D printing was superior to extrusion based printing to achieve the resolution demands for 3D printed ossicles. Resolution of modern imaging allows 3D reconstructions and 3D printing of human ossicles with good accuracy, though it is important to pay attention to thresholding during this process.

Lithospheric model along transect HT-1 across Western Carpathians and Pannonian Basin based on 2D integrated modelling

2D integrated modelling approach was applied to determine the lithospheric structure along transect HT-1 located in the Carpathian-Pannonian Basin–European platform region. Our approach combines simultaneous interpretation of surface heat flow, topography, gravity and geoid data. All available geophysical and geological data were used to create an initial model that has been afterwards modified by trial and error method until reasonable fit was obtained between input data and model predictions. The main focus of our study was the position and shape of the lithosphere-asthenosphere boundary (LAB). In the Pannonian Basin the modelled LAB is at depths of about 80–90 km and rapidly dips towards the Western Carpathians where its depth reaches values 145 to 150 km. Beneath the European platform the LAB depth is about 135–140 km. We can observe a slight lithospheric root under the Western Carpathians. This lithospheric thickening is interpreted as a small remnant of a subducted slab. This result is in a good agreement with the previous lithospheric models in the Carpathian-Pannonian Basin.