Surface Topography Measurement Research Articles

Carré Phase Shifting Algorithm for Wavelength Scanning Interferometry

Wavelength scanning interferometry is an interferometric technique for measuring surface topography without the well-known 2π phase ambiguity limitation. The measurement accuracy and resolution of this technique depends, among other factors, on the algorithm used to evaluate its sinusoidal interference pattern. The widely used fast Fourier transform analysis experiences problems such as waviness error across the measured surface due to spectral leakage. This paper introduces a new fringe analysis method based on the Carré phase shifting algorithm combined with a least squares fitting approach. Numerical simulation was carried out to assess the performance of the Carré algorithm in comparison to fast Fourier transform analysis, and the same was validated by presenting four experimental case study examples (a surface flat, a ceramic ball bearing, a flexible thin film, and a discontinuous step height sample). The analysis results show that the proposed Carré algorithm with least squares fitting can significantly eliminate the waviness error, especially when measuring steep surfaces.

The Use of a High-Pressure Water-Ice Jet for Removing Worn Paint Coating in Renovation Process.

The paper presents the results of investigations into the possibility of using ahigh-pressure water-ice jet as a new method for removing a worn-out paint coating from the surface of metal parts (including those found in means of transportation) and for preparing the base surface for the application of renovation paint coating. Experimental investigations were carried out in four stages, on flat specimens, sized S × H = 75 × 115 mm, cut from sheet metal made of various materials such as steel X5CrNi18-10, PA2 aluminium alloy and PMMA polymethyl methacrylate (plastic). In the first stage, the surfaces of the samples were subjected to observation of surface morphology under a scanning electron microscope, and surface topography (ST) measurements were made on a profilographometer. Two ST parameters were analysed in detail: the maximum height of surface roughness Sz and the arithmetic mean surface roughness Sa. Next, paint coatings were applied to the specimens as a base. In the third stage, the paint coating applied was removed by means of a high-pressure water-ice jet (HPWIJ) by changing the values of the technological parameters, i.e., water jet pressure pw, dry ice mass flow rate , distance between the sprinkler head outlet and the surface being treated (the so-called working jet length) l2 and spray angle κ for the following constants: the number of TS = 4 holes, water hole diameter φ = 1.2 mm and sprinkler head length Lk = 200 mm. Afterwards, the surface morphology was observed again and the surface topography of the specimen was investigated by measuring selected 3D parameters of the ST structure, Sz and Sa. The results of investigations into the influence of selected HPWIJ treatment parameters on the surface QF removal efficiency obtained are also presented. Univariate regression functions were developed for the mean stripping efficiency based on the following: dry ice mass flow rate , working jet length l2 and spray angle κ. Based on these functions, the values of optimal parameters were determined that allow the maximum efficiency of the process to be obtained. A 95% confidence region for the regression function was also developed. The results demonstrated that HPWIJ treatment does not interfere with the geometric structure of the base material, and they confirmed the possibility of using this treatment as an efficient method of removing a worn paint layer from bases made of various metal and plastic materials, and preparing it for applying a new layer during renovation.

Comprehensive visualization of spinal motion in gait sequences based on surface topography.

Analysis of spinal motion is considered to be important to assess function of the human spine. Surface topography (ST) is a method to record the vertebral orientation in 3D. Such measurements can be performed in static but also in dynamic situations like gait or other motion tasks. However, dynamic ST measurements are hard to interpret due to their complexity. The main goal of this paper is to provide comprehensive visualization tools which allow a more intuitive and comprehensive interpretation n of such measurements. In particular, juxtaposition and superimposition techniques are utilized to emphasize differences in motion characteristics. The method was applied to a test series of 12 healthy volunteers walking on a treadmill at various speed levels. It could be shown that the visualization tools are helpful to compare different motion sequences including an analysis of intra- and interindividual variation. Based on these techniques, it could be shown that the profiles of vertebral orientation remain considerable constant when one person was walking at different speed levels whereas they differed substantially between the different individuals. In contrast, the motion amplitudes contained high intra- and interindividual variation, i.e. between speed levels and different test persons. In summary, the paper demonstrates that appropriate visualization tools are helpful to interpret ST measurements and cope with the complexity of these data sets. In particular, they can be used to compare different motion sequences in a more comprehensive way.

On-machine measurement with an electrochemical jet machine tool

Measurement of surface geometry is an essential activity in engineering, which is commonly performed by tracing the surface of interest with a mechanical or an optical probe. This is generally performed ex-situ in laboratories designed for metrology. However, inline measurement represents an opportunity to unlock significant efficiency gains throughout manufacturing. Here, a new approach is proposed for in-situ measurement of surface topography using an electrolyte jet as a scanning probe within a precision electrochemical jet machine tool. The electrical resistance of a cylindrical jet impinging on a metal surface is a direct measure of the distance between the surface and the electrified nozzle, allowing profiling of surface shape. This enables integrated on-machine measurement in the electrochemical jet apparatus with tuneable sensitivity and vertical resolution, achieving accuracy of 4.4% with the calibration proposed here. The developed measurement system provides an accurate and low-cost surface imaging approach that can be easily integrated with industrial manufacturing processes.

Coatings strength evaluation of cutting inserts using advanced multi-pass scratch method

The strength of the cutting inserts coating significantly determines the tool wear and the quality of the machined surface. To determine the inserts coating strength, a new method of micromechanical evaluation was developed and tested. The method is based on multi-pass progressive sclerometry with a stepwise maximum indenter load increasing with each subsequent pass. On the first pass, the indenter load increased from zero to 300 mN in the middle of the scratch distance and decreased to zero at the end of the scratch distance. On each subsequent pass, the maximum load on the indenter was increased by a further 100 mN. The indenter loading and unloading rate were 13.4 mN/s. Coating failure criterion is defined as a significant change in the correlation tightness between successive scratches profilograms. The accuracy of determining the load at which coatings starts to fail depends on the step of increasing the indenter load. The developed method has been tested on various PVD coatings of inserts. Surface topography measurements of formed scratches confirms the coatings failure in area of maximum loads on the indenter.

Surface topography measurement of microstructures near the lateral resolution limit via coherence scanning interferometry

As a non-destructive method, coherence scanning interferometry is widely utilized for surface topography measurement of step microstructures in optical and integrated circuit fields. The measurements are always implemented near the lateral resolution limit of the system because the critical dimension of these microstructures is at the micron or sub-micron scale. However, in this case, not only is the image of microstructures blurred, but also the diffraction effects distort the measured topography near the step edges. The magnitude of distortion at a certain position appears to be related to its distance from the edges and the duty cycle of the microstructures. Therefore, it is necessary, although difficult, to improve the accuracy of topography measurement for microstructures if their images are blurred owing to the lateral resolution limit. When located far away from the step edges of microstructures, the coherence signals are normal and contain a single envelope with its peak corresponding to the surface height. However, the anomalous coherence signals containing two envelopes appear near the step edges. The peaks of these envelopes correspond to the top and bottom surfaces of step structures, thus distorting the coherence peak detection for topography measurement. Therefore, the primary issue is the determination of the correct envelope in the anomalous coherence signals that is achieved by distinguishing the current surface of step structures for each position. In this paper, we propose a binarization method based on edge localization to achieve surface distinguishment through the analysis of the contrast and intensity of the coherence signals. After determining the correct envelope, we construct a new form of wavelet family and employ the Morlet wavelet transform to calculate a split point for dividing the anomalous coherence signals. Finally, the effective coherence signals corresponding to the correct envelope are extracted. Surface topography measurement of the nanopillars on the metasurface is obtained from the extracted signals. These nanopillars are distributed with a varying duty cycle and their diameters range from 590 to 1350 nm, near the lateral resolution limit of 501.9 nm of the system. The topography of nanopillars is recovered from the field of view, while the diameter and height of different types of nanopillars are measured. The mean value and standard deviation of these two parameters are consistent with the results obtained via scanning electron microscopy.

In-situ 3D reconstruction of worn surface topography via optimized photometric stereo

Since worn surfaces contain rich information of the wear mechanisms, in-situ measurements of surface topography can characterize ongoing wear degradation in machines. With the help of photometric stereo vision, three-dimensional (3D) topography of worn surfaces is obtained with a monocular microscope. However, the accuracy of the reconstructed surfaces remains low due to the non-Lambertian reflections of worn surfaces and noise in the image acquisition equipment. To address this issue, an optimized photometric stereo approach is proposed for the improvement of worn surface reconstruction. To accommodate the non-Lambertian reflections, a multi-branch network is constructed to estimate normal vectors from both the photometric images and the incident illumination directions. The estimated normal vectors are adopted to reconstruct worn surface topography by embedding prior knowledge. With this design, the overall distortion caused by image noise is effectively suppressed. The proposed method is verified by comparing with the Laser Scanning Confocal Microscopy (LSCM). As the main result, over 88% similarity on the worn surface roughness can be obtained.

Influence of thermal disturbances on profilometric measurements of surface asperities

During the surface topography measurements, changes in the ambient temperature affect the elongation of both the tested object and the measuring device. This influence is insignificant and often negligible, when measuring a single two-dimensional profile, which lasts from a few to several minutes. However, during spatial measurements lasting over several hours, changes in the ambient temperature cause texture mapping errors. The research included assessment of impact of changes in the ambient temperature of a tactile profilometer on the results of surface topography measurements.In the paper methodology of surface topography measurements under controlled temperature conditions is described. Thermal influence of the environment on the errors in mapping of surface topography were also determined. Measurements were carried out in a specially designed climatic chamber. Results of multiple measurements of the same reference surface profile in constant and variable thermal conditions of the environment were presented. Such procedure allowed for the presentation of a two-dimensional transverse profile of a generated surface, varying as a function of temperature. Generated surfaces were parameterized and compared with each other. The results of the research allowed us to state that changes in the ambient temperature during the measurements of the surface topography affect the mapping errors of the measured structure. Temperature changes and measurement results are strongly linearly correlated with each other.

Characteristics of the Surface Topography and Tribological Properties of Reinforced Aluminum Matrix Composite.

Due to their excellent synergistic properties, Aluminum Matrix Composites (AMC) have achieved a high degree of prominence in different industries. In addition to strength, the wear resistance of materials is also an important criterion for numerous applications. The wear resistance depends on the surface topography as well as the working conditions of the interacting parts. Therefore, extensive experiments are being conducted to improve the suitability of engineering materials (including AMC) for different applications. This paper presents research on manufactured aluminum metal matrix composites reinforced with 10 wt.% of Al2SiO5 (aluminum sillimanite). The manufactured and prepared samples were subjected to surface topography measurements and to tribological studies both with and without lubricant using a block-on-ring tester. Based on the results, analyses of the surface topography (i.e., surface roughness parameters, Abbott–Firestone curve, and surface defects) as well as of the tribological characteristics (i.a. friction coefficient, linear wear, and wear intensity) were performed. Differences in the surface topography of the manufactured elements were shown. The surface topography had a significant impact on tribological characteristics of the sliding joints in the tests where lubrication was and was not used. Better tribological characteristics were obtained for the surfaces characterized by greater roughness (determined on the basis of both the profile and surface texture parameters). In the case of tribological tests with lubrication, the friction coefficient as well as the wear intensity was significantly lower compared to tribological tests without lubrication. However, lower values of the friction coefficient and wear intensity were still recorded for the surfaces that were characterized by greater roughness. The obtained results showed that it is important to analyze the surface topography because surface characteristics influence tribological properties.

Build orientation effect on Ti6Al4V thin-wall topography by electron beam powder bed fusion

Additive Manufacturing is a key enabling technology for Industry 4.0 and the Green Deal, allowing more efficient resources exploitation while providing innovative design to critical components. Electron Beam Powder Bed Fusion (EB-PBF) is an edge technology for many sectors, i.e. aerospace, medical, and automotive. The control of the surface finish by surface topography measurements is essential to engineer surface functional properties, whose specifications are application specific. This works investigates the effect of thin-wall orientation and surface inclination on the topography, described by areal field and feature parameters, to provide designers with a useful tool in the early stage of product development and tolerance specification and verification.

Measurement and Analysis of Three-Dimensional Surface Topography of Sawn Timber Based on Scanning Probe Method

In order to explore the characteristics of the three-dimensional surface morphology of sawn timber, a threedimensional wood surface morphology tester based on the scanning probe method and the principle of atomic force microscope was used to test the three-dimensional surface morphology of three kinds of sawn timber and calculate its surface roughness. This study also analyzed the reasonable plan for the value of wood surface roughness and the advantages of the three-dimensional shape tester, as well as the influence of tree species, three sections, air-dry density and other factors on the surface roughness of the specimen after mechanical processing. The results have shown that it is a more appropriate method to select the calculated values of Sa and Sq as the evaluation of the surface roughness of wood with random surface characteristics. The three-dimensional wood surface topography tester can efficiently, conveniently and accurately display the three-dimensional topography of wood at a micron-level resolution, and is characterized by high efficiency and good durability. The three-dimensional surface morphology characteristics of the three sawn woods correspond to their roughness. The surface roughness of woods is arranged as follows: Sitka spruce > Larch > Beech. For the same tree species, the roughness of the corresponding section after sawing is as follows: chordwise section > crosswise section > radial section. The radial section has lower roughness than the other surfaces. The surface roughness of the wood after sawing is mainly related to its air-dry density. The above is intended to provide a useful reference for the application of measuring and evaluating the surface roughness of sawn timber using the three-dimensional surface topography test method.

Contributions of holography to the advancement of interferometric measurements of surface topography

Two major fields of study in optics—holography and interferometry—have developed at times independently and at other times together. The two methods share the principle of holistically recording as an intensity pattern the magnitude and phase distribution of a light wave, but they can differ significantly in how these recordings are formed and interpreted. Here we review seven specific developments, ranging from data acquisition to fundamental imaging theory in three dimensions, that illustrate the synergistic developments of holography and interferometry. A clear trend emerges, of increasing reliance of these two fields on a common trajectory of enhancements and improvements.

High reflection surface topography measurement based on fringe projection phase method and multi-exposure image fusion technology

High reflection surface topography measurement based on fringe projection phase method and multi-exposure image fusion technology

Honing process parameters influence on surface topographies

Honing is a superfinishing process that generates fine surface topographies with interesting tribological properties. However the control of the process requires highly experienced operators. The selection of proper stones (abrasive grit size and type) is decisive for reaching the target topography. Furthermore, especially in the case of a feed controlled process, the stone expansion must be in adequacy with the selected stone. This paper proposes to investigate the effect of the abrasive grit size for different stone expansions on surface topographies generated during the honing process. Honed samples are produced by a specific test bench reproducing the honing kinematics and recording process induced forces. In total, two hundred forty areal surface topography measurements are analyzed and discussed alongside with the force measurements. A systemic analysis of a wide range of roughness parameters is performed. Results demonstrate that the grit size has a significant impact on the final topography signature. Furthermore, even though expansion speed was doubled, no obvious influence was observed on the surface roughness parameters except one (isotropy Str). Based on these observations it is suggested that the expansion speed has a limited impact on the number of grooves generated.

International comparison of flatness deviation in areal surface topography measurements

An international comparison of surface topography flatness deviation was carried out. The comparison involved twelve optical surface topography instruments (focus variation instruments, confocal microscopes and coherence scanning interferometers) from six European research laboratories. The results demonstrated the following: (i) The flatness varies orders of magnitude between instruments, dependent on the measurement principle. (ii) The ISO proposed procedure gives meaningful results, especially for instruments based on the confocal principle. (iii) The selection of the measurement artefact is especially important for focus variation measurements, where the flatness deviation is influenced by the surface texture of the used artefact. (iv) A tilt in the used optical flat can significantly influence the measured flatness deviation.

Standardizing resolution definition in scanning helium microscopy

Resolution is a key parameter for microscopy, but methods for standardizing its definition are often poorly defined. For a developing technique such as scanning helium microscopy, it is critical that a consensus-based protocol for determining instrument resolution is prepared as a written standard to allow both comparable quantitative measurements of surface topography and direct comparisons between different instruments. In this paper we assess a range of quantitative methods for determining instrument resolution and determine their relative merits when applied to the specific case of the scanning helium microscope (SHeM). Consequently, we present a preliminary protocol for measuring the resolution in scanning helium microscopy based upon utilizing appropriate test samples with sets of slits of well-defined dimensions to establish the quantitative resolution of any similar instrument.

Fracture Surface Behavior of 34CrNiMo6 High-Strength Steel Bars with Blind Holes under Bending-Torsion Fatigue.

The present study evaluates the fracture surface response of fatigued 34CrNiMo6 steel bars with transverse blind holes subjected to bending with torsion loading. The analysis of the geometric product specification was performed by means of height parameters Sx, functional volume parameters Vx, and fractal dimension Df. Surface topography measurements were carried out using an optical profilometer with focus variation technology. The experimental results show that the doubling the bending to torsion moment ratio B/T from B/T = 1 to B/T = 2, maintaining the same normal stress amplitude, greatly reduces both Sa, Vv as well as the fractal dimension Df of the analyzed specimen fractures by 32.1%, 29.8%, and 16.0%, respectively. However, as expected, a two-fold increase in the B/T ratio, maintaining the same normal stress amplitude, resulted in a larger number of cycles to fatigue crack initiation, Ni, which can be explained by the lower shear stress level. These experiments prove that parameters Sx, Vx, Df are smaller for larger Ni values, which is an important finding. In addition, it was found a high consistency of surface topography measurements for the two sides of the broken specimens. The proposed methodology is both reliable and applicable for other engineering applications involving different geometries and loading conditions.

Simultaneous film thickness and refractive index measurement using a constrained fitting method in a white light spectral interferometer.

Film is widely used in optoelectronic and semiconductor industries. The accurate measurement of the film thickness and refractive index, as well as the surface topography of the top and bottom surfaces are necessary to ensure its processing quality. Multiple measurement methods were developed; however, they are limited by the requirements of a known dispersion model and initial values of thickness and refractive index. Further, their systems are rarely compatible with surface topography measurement methods. We propose a constrained nonlinear fitting method to simultaneously measure the thickness and refractive index of film in a simple white-light spectral interferometer. The nonlinear phase extracted by the spectral phase-shifting is fitted with the theoretical nonlinear phase obtained by multiple reflection model. The constraints of nonlinear fitting are obtained by the interferometric signal of vertical scanning, reconstructed by the integration of the white-light spectral signal to avoid local minima. The proposed method does not require a priori knowledge of the dispersion model and initial values of thickness and refractive index, and its system is compatible with the vertical scanning interferometry (VSI) method to reconstruct the surface topography of the top and bottom surfaces of film. Three SiO2 films with different thicknesses are measured, and the results show that the measured refractive index is within the theoretical value range of wavelength bandwidth and the measured thicknesses are closely aligned with the values provided by the commercial instrument. The measurement repeatability of refractive index reaches 10-3. Measurements on a polymer film demonstrate that this method is feasible for measuring the film without a priori information.

µCT‐Based Topography Analysis of Inaccessible Surfaces Exemplified by a Biofouling‐Covered Plastic

AbstractThe measurement of surface topographies is usually restricted to surfaces that are directly accessible to tactile or optical sensing. With this paper, the application of micro‐computed tomography to measure characteristics of surfaces that are covered by solid films and thus not directly accessible is demonstrated. The method is first validated by comparative measurements of a plastic sample with µCT and conventional optical profilometry. Afterwards, the µCT‐based method is successfully applied to a polyhydroxybutyrate plastic sample covered by biofouling after exposure to marine environment, providing insight into the degradation processes.

Effect of different cleaning methods after surface treatment of dental ceramics on the surface characteristics and adhesion to resin-based luting agents

The aim of this study was to assess the efficacy of cleaning methods after the surface treatment of dental ceramics. Ceramic slabs (zirconia – Yz; lithium disilicate-reinforced glass – Ld; and porcelain – Pc), were submitted to different surface treatments (air abrasion for Yz and hydrofluoric acid etching for Ld and Pc), and after, six cleaning methods were tested: DW – distilled water for 60 s; AL – 70% alcohol for 60 s + DW; UDW – ultrasonic bath with distilled water for 60 s; UAL – ultrasonic bath with 70% alcohol for 60 s + DW; IVC – ivoclean for 20 s + DW; PAC – 37% phosphoric acid for 20 s + DW. Microshear bond strength to luting agent was tested after 24 h (baseline) or 6 months storage (aged) in water at 37 °C. Complementary analysis of failure pattern, surface topography and composition, and contact angle measurements were executed. The cleaning methods promoted similar bond strength for Ld and Pc, regardless of the condition (baseline and aged) and for Yz after aging. DW, AL, and PAC decreased the contact angle for Yz, while UAL decreased for Ld. Pc presented a higher wettability with UDW, UAL, and PAC. The use of IVC and PAC resulted in precipitates in the Pc surface. For Yz, more air-abrasion remnants were observed using DW; for both Ld and Pc, a higher presence of fluorine was observed in groups treated with IVC. Despite differences in surface composition, topography and contact angle measurements, after aging the bond strength to the tested ceramic materials was similar regardless of the different cleaning methods.