Search

Spatial data fusion algorithms are widely applied in dimensional metrology for quality assessment or surface reconstruction. Multi-sensor point cloud fusion combines the advantages of multiple sensors by merging their measurements into a single coordinate system and reducing the prediction uncertainty and systematic errors. Algorithms designed for these tasks employ many methods that require thorough evaluations through a common framework. To address this need, this paper proposes a framework for simultaneous registration and approximation, and introduces a reference data generator for unbiased evaluations of data fusion algorithms with heterogeneous and anisotropic noise assumptions for applications involving multiple sensors. The bias for the generated reference data is evaluated close to floating point accuracy, which validates the generation method, and uncertainty evaluation on ICP variants reveals that reference data is more suitable to evaluate point cloud fusion algorithms. The proposed framework and data generator allows developing and validating more accurate data fusion algorithms. [ABSTRACT FROM AUTHOR]

The structural resolution describes the ability of a measuring device to detect small structures on the surface of a component or test specimen by means of a quantitative value. However, the structural resolution in the computer tomograph depends on the object and must therefore be determined separately for each measurement task. The previous approaches to structural resolution determination are only related to test specimens. In this paper, less discrete approaches based on a circular pattern are presented, which can be integrated into the measured component. A voxel-based methodology as well as two surface-based methodologies are described. The investigation results regarding the effect of the component position on the structural resolution are obtained on the basis of real CT measurements. A comparison is also completed with the well-known hourglass method. The results show that the resolution depends on the object being measured, with similar values being obtained for the same object using different methods.

A method is described to measure the thermal expansion coefficient of fused quartz glass. The measurement principle is to monitor the change in resonance frequency of a Fabry–Perot cavity as its temperature changes; the Fabry–Perot cavity is made from fused quartz glass. The standard uncertainty in the measurement was less than 0.6 (nm · m - 1) · K - 1 , or 0.15 %. The limit on performance is arguably uncertainty in the reflection phase-shift temperature dependence, because neither thermooptic nor thermal expansion coefficients of thin-film coatings are reliably known. However, several other uncertainty contributors are at the same level of magnitude, and so any improvement in performance would entail significant effort. Furthermore, measurements of three different samples revealed that material inhomogeneity leads to differences in the effective thermal expansion coefficient of fused quartz; inhomogeneity in thermal expansion among samples is 24 times larger than the measurement uncertainty in a single sample. [ABSTRACT FROM AUTHOR]

The structural resolution describes the ability of a measuring device to detect small structures on the surface of a component or test specimen by means of a quantitative value. However, the structural resolution in the computer tomograph depends on the object and must therefore be determined separately for each measurement task. The previous approaches to structural resolution determination are only related to test specimens. In this paper, less discrete approaches based on a circular pattern are presented, which can be integrated into the measured component. A voxel-based methodology as well as two surface-based methodologies are described. The investigation results regarding the effect of the component position on the structural resolution are obtained on the basis of real CT measurements. A comparison is also completed with the well-known hourglass method. The results show that the resolution depends on the object being measured, with similar values being obtained for the same object using different methods. [ABSTRACT FROM AUTHOR]

Copyright of Technisches Messen is the property of De Gruyter and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cupronickel-based alloys are widely known for their excellent resistance against aqueous corrosion, however, they can be susceptible to corrosion at accelerated rates and premature failure when exposed to a polluted or brackish seawater medium, even for short-term exposure durations. This unfamiliar corrosion behavior may be a result of the formation of an unprotected corrosion film during the early exposure durations. The paper investigates the corrosion phenomenon in cupronickel 90/10 alloy, by exposing the coupons in two different seawater compositions in the Arabian Sea region. Corrosion losses were investigated on the experimental coupons in a submerged position, for a maximum exposure duration of 150 days, using the conventional weight loss method and a new dimensional metrology-based measurement technique. Additionally, in this research the tubes of a marine heat exchanger having similar material that failed prematurely during operation in the Arabian Sea were also investigated for corrosion losses, followed by the characterization of the corrosion deposits using following analytical techniques: SEM, EDS, XRD and Raman Scattering. The experimental results showed significantly higher corrosion losses on coupons exposed to seawater site rich in pollutants and nutrients including dissolved inorganic nitrogenous compounds, compared to those subjected to a natural seawater solution in corrosion tanks maintained in a controlled environment. [ABSTRACT FROM AUTHOR]

Since X-ray computed tomography (CT) can analyse non-accessible features and parts in a non-destructive way, it enables the inspection of the individual components of assemblies in the assembled state. Such unique inspection capability is of great relevance because, even when each part of an assembly meets the specified tolerances, the proper functioning of the assembled system is not guaranteed, as variations can occur during the assembly operations, for instance due to clamping and/or assembly forces. Besides the dimensional evaluation of components in the assembly state, contact surfaces/interfaces and micro-gaps between coupled assembled components are in many cases important to be accurately identified and measured. These evaluations can be more easily conducted on multi-material assemblies in which the materials of the single components are characterized by different densities and characteristics, thus enabling their mutual distinction and segmentation within the CT reconstructed volume. In the case of mono-material assemblies, instead, due to the single X-ray attenuation coefficient to be considered, the three-dimensional model of the assembly resulting after CT reconstruction would appear as a unique and continuous volume in regions where components are in contact, with serious difficulties in evaluating their interface. To overcome this limit, the present research was aimed at developing new CT-based methods to enable a complete evaluation of mono-material assemblies. Such methods were applied to titanium dental implant systems, for which an accurate analysis of contact surfaces and interfaces between the assembled components is crucial to ensure perfect sealing and prevent mechanical failures as well as microbiological leakage and consequent bacteria infiltrations. Finally, the accuracy of the obtained measurement results is evaluated using a reference object made of titanium, featuring different calibrated micro-gaps. • CT reconstructions of mono-material assemblies appear as a unique and continuous volume. • Evaluating the interface where components are in contact is hence difficult. • Methods are developed to enable CT analyses of contact surfaces in mono-material assemblies. • The methods are applied to titanium dental implant systems. • The results accuracy is determined using a reference object with calibrated micro-gaps. [ABSTRACT FROM AUTHOR]

This paper provides an overview of state-of-the-art sensing and machine learning technologies for intelligent measurement in smart and precision manufacturing. Length, angle, and force are identified as the fundamental quantities for production quality management based on process monitoring as well as geometrical metrology in optical lithography and mechanical machining. Advancements in length-based measurement technologies such as laser interferometers and optical encoders, as well as advancements regarding depth and thickness measurements, are presented. Various types of optical microscopes, such as evanescent field microscopes, structured illumination microscopes, and confocal microscopes, are also described. For angle-based measurement technologies, in addition to the conventional continuous-wave laser autocollimators, the newly developed Fabry–Pérot angle sensor and nonlinear optics angle sensor using an ultrashort pulse laser are presented. Finally, on-machine and in-process force sensing and machining learning techniques for dimensional and machining process monitoring are reviewed. [ABSTRACT FROM AUTHOR]

X-ray computed tomography (CT) is increasingly used in industrial dimensional metrology. However, the establishment of metrological traceability can be challenging for CT dimensional measurements, as the evaluation of their uncertainty is generally non-trivial. Moreover, uncertainty determination becomes even more difficult when dealing with complex measurement tasks, such as in the case of lattice structures produced by additive manufacturing, characterized by features not accessible from the outside and/or by complex surface topographies, which are problematic to be calibrated using other measuring principles to ensure sufficiently low calibration uncertainty. This paper presents a critical investigation of two different experimental approaches for the uncertainty determination of CT dimensional measurements performed on components with inaccessible and/or complex geometries, as well as complex surface topography. The first approach, the "substitution method", is applied in this work using a newly developed reference object as the basis for the uncertainty assessment procedure through substitution measurements. The second one, the "multiple measurements approach", is based on repeated measurements both on the uncalibrated workpiece in multiple orientations and on simple calibrated standards. This second approach, initially introduced some years ago for tactile coordinate measuring machines, is now investigated in this work for its application to CT metrology. The two approaches are discussed and compared through an industrial case study: the dimensional verification of lattice structures fabricated by metal additive manufacturing. For the selected case, both approaches yielded comparable measurement results and uncertainties. Finally, the multiple measurements approach was further investigated by applying it to the CT measurement of the calibrated object. The paper also discusses the open issues of both methods and outlines directions for future investigations. [ABSTRACT FROM AUTHOR]

The metrological structural resolution (MSR) describes the size of the smallest surface feature that can be measured dimensionally with a given accuracy. Several methods to determine the MSR for dimensional x-ray CT (dXCT) have been proposed in the past, two of which are compared and related in this publication, i.e. the curved-edge based (CEB) and the profile-based spectral (PBS) method. Both methods consider the surface structure as being described by a single surface on the relevant local scale and are also suitable for the application to optical or tactile coordinate measurement systems (CMSs). The CEB method evaluates the radii of circular shapes to determine the width of the Gaussian filter that describes the filtering of the surface by the CMS. The PBS method evaluates the instrument transfer function (ITF) determined by means of the measurement of a surface profile with a broad-band spatial frequency spectrum with a finite cut-off frequency. The PBS method yields the threshold wavelength for which the amplitude of the ITF drops below a certain level. While the resulting quantities of the two methods are very different they evaluate the same characteristic of the CMS. In this publication an analytical relation between those results is derived and shown to exist which is used to define the MSR. Simulated CT scans as well as dXCT measurements are performed to verify this relation. The results for the MSR obtained from both methods are consistent and deviations to the expectations based on theory are within a reasonable range. [ABSTRACT FROM AUTHOR]

New automated laser radar measurement systems at the Saab Inc. West Lafayette, USA, facility will make airframe assembly of the aft body for the new eT7-A aircraft a quicker, more cost-efficient process. Digital twin concepts realized through simulation and off-line programming show advantageous results when studying future state scenarios or investigating how a current large-volume dimensional metrology system acts and behaves. The aim of this exploration has been to examine how to facilitate the design and programming of automated laser radar concepts by means of novel simulation-based software. High-speed computing algorithms efficiently solve tasks and sequence problems related to many statistical combinatorial possibilities in calculations. However, this approach requires accurate and reliable models and digital twins that are continuously updated with real world data and information. In this paper, the main contributions are to create procedures to define the dimensional metrology workflow at Saab and to model and simulate the laser radar process, enhancing and tailoring existing offline programming software by specific new functionalities. A case study conducted at Saab Aeronautics premises in Linköping acted as a clinical laboratory to generate our research findings. The exploratory work indicates that a reliable simulation-based development method can be used advantageously in the early-stage design layout of automated dimensional metrology systems to verify and guarantee the line-of-sight of, e.g., a laser light path and its allowed inclinations to a specific geometrical feature to be measured, extracted, and evaluated.

The selection methodology for thickness loss measurement is very important to determine the extent of corrosion damage, as well as in formulation of corrosion prediction models and inspection/maintenance plans for offshore structures. This paper introduces a more accurate corrosion measurement technique, based on the pre-exposure dimensional metrology and post-exposure optical microscopy/image analysis on the cross-sections of steel samples. During this corrosion test, the surface grinded and uncoated steel samples were submerged vertically in an artificial seawater solution, for a duration of up to a maximum of 365 days. The corrosion damage experienced on the steel samples means that the dimensional metrology can be more accurate, and useful approach to measure both uniform and localised corrosion losses simultaneously than the conventional average mass loss method. [ABSTRACT FROM AUTHOR]

The challenges of choosing an optimally thick surface plate (SP) were noticed during the calibration of pressure measuring instruments against pressure balance type primary and secondary standards. This has motivated authors to investigate this issue in detail. It is observed that the traditional workstation made of steel sheets may not be flat enough to generate accurate pressure measurement results. These SPs are also regularly used in the metrology laboratories, inspection rooms, and manufacturing industries. Whenever precise and accurate measurements and inspections are performed, the irregularities of the working surfaces lead to incorrect results. Therefore, focused research is carried out by analyzing some of the standard granite plates. Usually, manufacturers design, fabricate, and install the SPs as per the recommendation of the respective documentary standards. The standards provide the requirements and specifications of the flatness tolerances for different sizes of the SPs. However, these standards do not precisely specify the optimum thickness of the SP. Standards also suggest using finite element analysis to avert complex mathematical procedures. The simulation method precisely represents the individual case of installation/design. Therefore, the bending cases due to self-weight and rigidity tests are simulated to determine the deformations of the various sizes of granite SPs. Their results led to devising the proposed optimization of the thickness of metrological surface plates. In the present investigation, granite SPs of different sizes are simulated. The critical thickness is observed when the deformation reduces to its optimum level. The surface deflection against the load is minimum at critical thickness values. The results obtained in the optimization are compared with the standard values. [ABSTRACT FROM AUTHOR]

Traceability is a fundamental issue for ensuring accuracy of nanometrology. A shortened traceability chain is advantageous for reducing calibration steps, thus reducing errors and raising application efficiency. A novel kind of two-dimensional grating is manufactured by atom lithography, whose pitch and (orthogonal) angle values are directly determined by natural constants, offering a feasible approach for effectively shortening the traceability chain. The PTB’s calibration results show that the two-dimensional grating has excellent orthogonality with a deviation of only 0.001°. The application of two-dimensional grating is demonstrated for the characterization of the angular distortion of a SEM, showing its great application potential.

In the industry of manufactured and assembled devices, the miniaturization and integration of small components with feature sizes on the order of 10 mm or smaller leads to new demands for inspection measurement systems. There are requirements for higher levels of resolution, precision, and accuracy, ideally with technologies that measure internal features and avoid causing damage to the original device. Three-dimensional (3D) techniques such as X-ray computed tomography (CT) may be used to non-destructively inspect internal geometries, or features, that are difficult to reach (or impracticable to access) with tactile probes. Traditional CT systems are, however, limited in resolution and achievable measurement accuracy. One alternative would be to use higher resolution instruments such as 3D X-ray microscopes and expand their measurement capabilities to the field of high precision metrology. This paper demonstrates how to perform non-destructive inspection in small-scale volumes, using a field-of-view (FOV) of about 5 mm diameter, and achieve dimensional measurements that are highly repeatable and accurate (with deviations from calibrated data within the ±1 μm range). This capability is relevant for the electronic industry, e.g., for measurements of camera modules or injection molded connectors, and for manufacturing highly efficient components, e.g., fuel spraying injectors and additive manufactured components with small internal features.

New automated laser radar measurement systems at the Saab Inc. West Lafayette, USA, facility will make airframe assembly of the aft body for the new eT7-A aircraft a quicker, more cost-efficient process. Digital twin concepts realized through simulation and off-line programming show advantageous results when studying future state scenarios or investigating how a current large-volume dimensional metrology system acts and behaves. The aim of this exploration has been to examine how to facilitate the design and programming of automated laser radar concepts by means of novel simulation-based software. High-speed computing algorithms efficiently solve tasks and sequence problems related to many statistical combinatorial possibilities in calculations. However, this approach requires accurate and reliable models and digital twins that are continuously updated with real world data and information. In this paper, the main contributions are to create procedures to define the dimensional metrology workflow at Saab and to model and simulate the laser radar process, enhancing and tailoring existing offline programming software by specific new functionalities. A case study conducted at Saab Aeronautics premises in Linköping acted as a clinical laboratory to generate our research findings. The exploratory work indicates that a reliable simulation-based development method can be used advantageously in the early-stage design layout of automated dimensional metrology systems to verify and guarantee the line-of-sight of, e.g., a laser light path and its allowed inclinations to a specific geometrical feature to be measured, extracted, and evaluated. [ABSTRACT FROM AUTHOR]

In this paper, we present the roundness measurement capability and traceability at CSIR National Physical Laboratory-India (NMI-India). A glass hemisphere is used for traceability, and measurements are taken with a roundness machine. The LSC method with the minimum zone solution is used for the analysis of results for circular profiles. The measurement uncertainty for the glass hemisphere calibration using roundness machine is ± 0.017 µm. [ABSTRACT FROM AUTHOR]

The increasing demands of highly precise industrial products lead to continuous seeking for the improvements in cabapility of manufacturing machines, i.e., machine tools. Machine tools include different types of manufacturing machines, i.e., turning, lathe, drilling, and milling machines whatever computerized numerical control (CNC) type or manual type. The cabaplity improvement in machine tools requires a real understanding of their productivity, accuracy, and operating parameters, i.e., their geometrical errors. These errors can be accurately identified through measurements with highly accurate measuring instruments. These machine errors have different error sources. The angular errors, horizontal and vertical straightness errors, paralleism errors, and squarness errors are clear examples for these sources. In this work, a comparative study for the determination of machine tools errors is carried out. Two main instruments of laser interferometer system and autocollimator system are used. The geometric errors are identified, measured, and analyzed. [ABSTRACT FROM AUTHOR]

X-ray computed tomography (XCT) enables the dimensional measurement and inspection of highly geometrically complex engineering components that are unmeasurable using optical and tactile instruments. Conventional XCT scans use a circular scan trajectory where X-ray projections are acquired with a uniform angular spacing; this approach treats all projections as being of equal importance, in practice, some projections contain more object information than others. In this work we capitalize on this concept by intelligently selecting projections with a view to improve the quality of surface models extracted from an XCT data-set. Our approach relies on using a priori object information to select X-ray projections in which the surfaces of the object are aligned with a ray-path, thus ensuring the surface of the object is fully sampled. Results are presented showing that the proposed method is able to reduce CAD comparison errors by 16%, reduce surface form error by 3%, and improve edge contrast by 14% for a machined aluminium component. [ABSTRACT FROM AUTHOR]

The paper presents the transformations taking place in length and angle metrology related to Metrology 4.0, a measurement strategy resulting from Industry 4.0. Metrology in an industrial conditions is gradually focusing more and more on advanced measurement systems. The coming reality will see the development of communication between systems and their components, as well as the individual sensors belonging to them. The Internet of Things and artificial intelligence as well as the possibility of using augmented or virtual reality will play a momentous role. The demand for these technologies results in the development of new specialized software and hardware solutions, the use and availability of which are diametrically different compared to the past. Also, the use of AI and cybersecurity in metrology is a topic that is receiving increasing attention. Metrology 4.0 is therefore becoming a very important part of the functioning of industry, changing the philosophy and organization of measurements carried out on the basis of new measurement techniques. [ABSTRACT FROM AUTHOR]

Real-time inspection of large mechanical parts manufacturing using camera-based scanning systems are increasingly adopted in industry 4.0. It leads to take preventive actions during the manufacturing process and then to fabricate mechanical parts right-first-time with respect to specified tolerances. Therefore, the use of camera-based scanners requests a preliminary calibration process. It consists on estimating the intrinsic and extrinsic parameters required to relate the 3D world point to its projection on the image plane. Since selection of the calibration grid poses affect the calibration quality, one approach-based machine learning (ML-approach) is proposed including the polynomial approximation of the reprojection errors function of 6 degree of freedom (DoF) combined with particle swarm optimization (PSO). Synthetic and experimental evaluations have been performed while assessing the performance of the proposed ML-approach. The synthetic evaluation reveals a better convergence of the intrinsic and extrinsic parameters in comparison to recent published calibration methods by Wizard (CW-method) and Rojtberg (R-method). The experimental evaluation of the ML-approach shows an average error R E < 12 µm and a sub-micrometre repeatability, which confirm the benefit of using machine vision-based scanning systems for the inspection of large volume parts in real time. [ABSTRACT FROM AUTHOR]

Gauge blocks are an important basis for maintaining traceability in dimensional metrology, used for calibrating length measuring instruments and for adjustments in all branches of manufacturing. Their important feature is that they can be wrung with small dimensional uncertainty. An overview of the factors influencing the accuracy of a stack length, such as the quality of the gauge blocks (grade, wear), surface preparation (cleaning and usage of a lubricant), wringing (way and time, temperature of hands and gloves) is given in the paper. Experiments for determining these influences were performed with a highly precise gauge block comparator. Proper selection of gauge blocks, preparation of their surfaces and oiling improve the accuracy of a stack length. Application of a lubricant, wiped with a dry cloth or paper towel, helps to wring them more easily, but its contribution to the stack length in the experiment was 0.1 μm for oil and 0.2 μm for grease. Temperature changes of gauge blocks were estimated by holding them, and, during wringing in well controlled air conditions, monitoring them to yield the empirical coefficients of their warming up. The results showed that usage of gloves reduces the warming up by approximately half, but still the stack must be stabilised in well controlled conditions for at least one hour if it is used for micrometre-level precise measurements. [ABSTRACT FROM AUTHOR]

X-ray Computed Tomography (XCT) has become a common tool for dimensional analysis as it allows for non-destructive internal and external measurements. Manufacturers often specify the accuracy of dedicated metrology XCT systems as a maximum permissible error (MPE) statement determined using workpieces, test lengths and positions that are significantly different between manufacturers. The VDI/VDE 2630-1.3:2011 guideline provides specification and respective test methods to verify performance against these MPE statements and has been applied in this study to evaluate four different commercial XCT systems in a uniform way. For this examination a multi-sphere test object was developed that explicitly complies with these guidelines and maximises the use of the whole measurement volume, which has then been scaled to test both high and low magnifications. The study consisted of two parts: scans according to a protocol to allow for a fair comparison between all the systems and free scans where manufacturers could show the best capabilities of their system. With these particular objects no system complied with its own MPE statement, however sub voxel accuracies were found. The maximum error in terms of voxels ranged between 0.16 voxel to 0.43 voxel for low magnification (voxel size of 100 μm) and 0.49 voxel to 0.82 voxel for high magnification (voxel size of 14 μm) between systems. This indicates the need for greater standardisation and transparency on how accuracy statements are determined, and more directed protocols for testing the performance of a system. In particular due to the extreme range of measurement volumes and voxel sizes/resolutions XCT are capable of, it is demonstrated that it maybe reasonable to consider an MPE dependent on voxel size. • The performance of four different commercial XCT systems was evaluated. • For testing a reference standard has been designed according to the VDI/VDE 2630 guidelines. • With this design no system complied with its maximum permissible error statement. • Every system achieved sub-voxel errors for large and small measurement volumes. [ABSTRACT FROM AUTHOR]

Computed Tomography (CT) as a dimensional metrology tool allows test parts to be fully characterized regardless of whether their features are accessible from the outside or hidden from sight. CT, however, has a complex measurement chain and the measurement accuracy can be strongly affected by metrologist-selected scan parameters. To develop a broader understanding of the effect of different factors on the dimensional content, this paper presents the construction of the digital representation of a CT measurement process using a simulation tool and the utilization of the virtual environment to study the relationships between input parameters and dimensional features of a prismatic test part. [ABSTRACT FROM AUTHOR]

To address the challenge of climate change, future energy systems need to have reduced greenhouse gas emissions and increased efficiencies. For solid fuel fired combustion plants, one route towards achieving this is to increase the system's steam temperatures and pressures. Another route is to co-fire renewable fuels (such as biomass) with coals. Fireside corrosion performance of two candidate superheater/reheater alloys has been characterised at higher heat exchanger surface temperature. Samples of the alloys (a stainless steel, Sanicro 25 and a nickel-based alloy, IN740) were exposed in fireside corrosion tests at 650 °C, 700 °C and 750 °C, in controlled atmosphere furnaces using the 'deposit recoat' test method to simulate superheater/reheater exposure for 1000 h. After exposure, the samples were analysed using dimensional metrology to determine the extent and distributions of corrosion damage in terms of surface recession and internal damage. At 650 °C, the stainless steel and nickel-based alloy performed similarly, while at 700 °C and above, the median damage to the steel was at least 3 times greater than for the nickel-based alloy. Optical and electronic microscopy studies were used to study samples' damage morphologies after exposure. Intergranular damage and pits were found in sample cross sections, while chromium depletion was found in areas with internal damage. For high-temperature applications, the higher cost of the nickel-based alloy could be offset by the longer life they would allow in plant with higher operating temperatures. [ABSTRACT FROM AUTHOR]

To address the challenge of climate change, the energy sector is developing novel strategies to reduce greenhouse gas emissions. One route is to increase steam temperatures and pressures (above 650°C and 350 bar). Another route is the use of potential net zero emissions fuels, like biomass. Both these routes cause issues for the heat-exchanger materials due to the differences in composition of the combustion environments generated, compared to coal. This paper characterises candidate superheater/reheater alloys' behaviour (Sanicro 25 and IN740) at 700°C. 1,000 h fireside and 10,000 h steamside exposures were carried out, the first using 'deposit recoat' techniques. Sample cross-sections were analysed using dimensional metrology and SEM/EDX. Fireside results for Sanicro 25 showed degradation throughout the samples' thicknesses. In steamside exposures, Sanicro 25 formed a Cr-rich scale, and Nb rich particles (z-phase). IN740 showed lower metal and sound metal damage than Sanicro 25 for fireside and steam oxidation exposures. [ABSTRACT FROM AUTHOR]

This paper evaluates the dimensional accuracy of industrial X-ray computed tomography (CT) measurements as a function of the geometric magnification (M g) used for CT scanning. Two plates of square-shaped geometry with 28 drilled holes, one made of aluminum (48 mm × 48 mm × 8 mm) and a second one made of steel (6 mm × 6 mm × 1 mm), are used as measuring workpieces to test fourteen different magnification axis positions in a metrology-grade X-ray CT system. In addition to measuring the diameter and roundness of each hole, distance measurements between the holes are evaluated—both as uni-directional (center-to-center) and bi-directional (point-to-point or edge-to-edge) lengths. The variance of CT dimensional measurements, with respect to reference data obtained from tactile coordinate measurement machines (CMMs), is studied. It is found that the measurement deviations for uni-directional distances are approximately independent of M g and mostly within a ± 4 μm range. In contrast, for measurements of diameter, roundness, and bi-directional lengths, the deviations between CT and CMM data extend outside the ± 4 μm limits and strongly depend on M g (which is a variable inversely proportional to the voxel size of CT scan, V X). More specifically, decreasing M g or, equivalently, increasing V X , generally leads to larger deviations in the dimensional data. To include the magnification dependence on the estimations of CT measurement deviations, based on the experimental data presented throughout this paper, the authors propose that the maximum error of CT length measurements can be expressed as E m a x = (A + X / B + L / K) μm, with A , B , and K being constant factors (determined for a particular CT measuring setup), L the dimension of the measuring length (in mm), and X the magnification axis position of the CT scanner (also in mm). Whereas the term " L / K " considers error influences from the size of the sample, the term " X / B " accounts for influences from magnification (and voxel size) selections during CT measurement. • X-ray computed tomography (CT) is studied via changes of geometric magnification M g. • Errors of uni-directional center-to-center distances are approx. independent of M g. • Errors of form and bi-directional lengths strongly depend on M g (and voxel size V X). • Dimensional accuracy of CT data deteriorates as M g lowers and the V X grows. • A model that includes M g is proposed for estimating maximum CT measurement errors. [ABSTRACT FROM AUTHOR]

We characterised the displacement of a transmission X-ray tube target parallel to the beam axis due to thermal effects using interferometry. Displacements of up to 10 μm with a sensitivity of about 0.4 μm/W deposited power were measured relative to the X-ray tube's mechanical mounting position. They significantly influence the scale factor of dimensional computed tomography measurements by several 10−4 at high geometric magnifications. Finite element simulations revealed that the displacement is due to thermal deformation of the entire target assembly and helped to derive a linearised model that predicted the displacements within a few tenths of a micrometre. Radiographic measurements of a calibrated standard confirmed that the mechanical displacement of the target corresponded with the X-ray focal spot position. The findings help to increase the accuracy of dimensional X-ray computed tomography measurements and to ameliorate the design of transmission X-ray tubes. [Display omitted] • Direct interferometric displacement measurement of an X-ray tube transmission target. • Finite element simulations revealed the underlying thermo-mechanical mechanisms. • A linearised model predicted the target position with sub-micrometre accuracy. • Confirmation by radiographic measurements of a calibrated standard. • Reduction of scale errors in high-magnification dimensional X-ray computed tomography by up to an order of magnitude. [ABSTRACT FROM AUTHOR]

Corrosion rates in marine structural steels differ significantly with the varying compositions of seawater particularly near harbours or coastal regions primarily due to the presence of untreated chemically active species from various sources. The reviewed literature reports accelerated steel corrosion losses in coastal seawater exposure conditions, which has widely been attributed to the presence of aggressive chemical compounds e.g., dissolved inorganic nitrogenous (DINs) compounds, sulphur containing compounds, in combination with various other environmental factors and their interdependent complex relationships. This paper aims to investigate the influence of nitrates, a DIN compound, on the corrosion behaviour of a low carbon ship structural steel, by exposing surface the cleaned coupons to an artificial seawater solution in a controlled laboratory environment. The uniform and localised corrosion damages were measured on steel coupons by using the standard weight loss and the dimensional metrology methods. A significant increase in corrosion losses was observed on coupons exposed to the nitrate-added artificial seawater than those exposed to similar seawater compositions with no additional nitrate content. Elemental compositions of corrosion deposits and corrosion morphologies investigated using various analytical tools such as SEM, EDS and Raman scattering techniques have shown different types of corrosion products in both exposure conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

• XCT's capability for dimensional metrology of AM parts is verified by CMS. • XCT beam hardening and XCT voxel size scale error are both investigated. • A new 3D algorithm to estimate uncertainty of the CMS mechanical filtering effect. • Simulation of CMS and XCT are conducted by virtual part with the AM surface texture. This paper aims to verify the capability of X-ray Computed Tomography (XCT) in the dimensional measurement of additive manufacturing (AM) parts by comparing it against a tactile coordinate-measuring system (CMS). Three factors are investigated: XCT beam hardening, XCT voxel size scale error, and CMS mechanical filtering effect. Their performances are compared via both physical and simulation experiments. The physical experiments show that the employed XCT beam hardening elimination aids in obtaining accurate inner dimensions but deteriorates external dimension measurements. XCT voxel size scale error can be compensated by either the two-sphere calibration or the CMS normalisation method. The physical measurement results also indicate that the dimensional deviation between XCT and CMS measurements is mainly due to the mechanical filter effect of CMS, which is further sustained by simulation measurements. The proposed 3D CMS probe scanning simulation method yields a reliable uncertainty estimation of the CMS mechanical filtering effect. [ABSTRACT FROM AUTHOR]

The article describes an approach to measure child growth using a coordinate measuring arm. For this purpose, a test set up has been built to measure the lower leg length directly on the knee surface and with the help of a plate. The use of the plate resulted in the distribution of pressure on the surface to be measured. Based on the results, the LLV (a lower leg growth velocity) was determined and studies were carried out to estimate the uncertainty of this factor. The obtained LLV results at 0.4 mm/week, correspond to the results of studies conducted on specialist test set-ups for knemometric measures described in the literature. The obtained results also allow recognizing periods of good health and bad health of the child.

A study of the secondary source phenomenon due to the presence of off-focal radiation in industrial micro-focus cone-beam X-ray computed tomography (XCT) systems and its influence on dimensional measurements is presented. Although off-focal radiation production within X-ray tubes has been studied for medical X-ray imaging systems, its properties and its effects on dimensional measurements in industrial XCT systems have not been discussed prior to this research. The study comprises: evaluation of the geometrical properties of off-focal radiation through a theoretical and experimental study of two-dimensional projection images of the scanned objects, verification of these properties using computer simulations and evaluation of the impact of the secondary source on dimensional measurements using experimental and simulation approaches. In addition, ways to minimise the effects of off-focal radiation are discussed, and reference samples for characterising the properties of off-focal radiation are proposed. • Off-focal radiation in industrial micro-focus cone-beam X-ray computed tomography systems. • Influence of off-focal radiation on dimensional measurements. • Reference samples to evaluate off-focal radiation. • Minimisation of off-focal radiation. [ABSTRACT FROM AUTHOR]

Large Volume Metrology is essential to many high value industries to go towards the factory of the future, but also to many science facilities for fine alignment of large structures. In this context, we have developed a multilateration coordinate measurement system, traceable to SI metre, and suitable for outdoor measurements or industrial environments. It is based on a high accuracy absolute distance meter developed in-house and shared between several measurement heads by fibre-optic links. Thus, from these measurement stations, multiple distance measurements of several positions of a target can be performed. At the end, coordinates of the heads and of the different target locations are determined using a multilateration algorithm with self-calibration. In this paper, the uncertainty of this multilateration coordinate measurement system is determined with a consistent metrological approach. First, 13 different sources of errors are listed and quantified. Then, thanks to Monte Carlo simulations, the standard uncertainty on a single absolute distance measurement is assessed to 4.7 μm. This includes the uncertainty contribution of the telemetric system itself, but also the contributions of the mechanical designs of the measurement heads and the target. Lastly, measurements of three-dimensional coordinates of target positions are performed in a control environment, then in a large workshop without temperature control: these measurements validate the uncertainty assessment of the system. • Multilateration coordinate measurements are less sensitive to temperature gradients. • Absolute distance meters are suitable for outdoors or harsh industrial environments. • Self-calibration algorithm does not induce a significant additional uncertainty. [ABSTRACT FROM AUTHOR]

Estimates of the measurement uncertainty are crucial, without which precision measurements are useless from a practical point of view. Dimensional compliance with geometric product specifications (GPS) plays a key role in decision-making in manufacturing engineering. Without rigorous uncertainty assessment, manufacturers risk making incorrect decisions. Coordinate measuring machine (CMM) measurements are suitable when complex measurement tasks of a workpiece must be made, such as measurements of positional tolerances or repetitive measurements. Here, we attempted to solve problems related to the thermal influences in the assessment of uncertainty in Coordinate Metrology. Task-specific experiments based on the identification of residual errors using a hole plate standard calibrated by Physikalisch-Technische Bundesanstalt (PTB) were performed to compare the measurement uncertainty results in the different temperature ranges. The thermal issues of CMMs include measurements of the temperature of the environment and CMM errors, estimation of the uncertainties of the thermal errors of the CMM, and reduction of the uncertainties related to thermal errors of CMMs. Computation of the thermal errors must account for environmental influences and internal heat sources of the CMM. Assessment of the uncertainty of thermal errors covers almost all factors related to the uncertainty of the CMM. The state-of-the-art technique for determining the uncertainty of the measurements is discussed. [ABSTRACT FROM AUTHOR]

The substitution method—an empirical approach for uncertainty assessment (adapted from the ISO 15530-3 guidelines) that is based on a comparison between repeated measurements of a calibrated standard workpiece and measurements of a test (uncalibrated) sample—has been the approach most adopted over the past decade for estimation of measurement uncertainties in dimensional metrology with X-ray computed tomography (CT). However, questions about how to apply the substitution (or use calibrated workpieces) for X-ray CT metrology persist because the substitution method does not always encompass all the most relevant CT measurement influencing factors. This paper discusses some issues with the direct application of the ISO 15530 series for the estimation of CT measurement uncertainties and reviews other empirical methods that can be applied in uncertainty analyses in CT metrology. Special attention is placed to the treatment of uncertainties in the case of 'uncorrected' measurement results (i.e., not compensated for bias), which for X-ray CT has traditionally been limited to the use of the root-sum-of-squares of standard uncertainties (RSSu) approach. This article investigates other possibilities for uncertainty estimation of 'uncorrected' results that could be applied to CT measurements, namely the root-sum-of-squares of expanded uncertainties (RSSU), the algebraic sum of expanded uncertainty with the signed bias (SUMU), the enlargement of the expanded uncertainty by adding the absolute value of the bias (SUMU MAX), and the so-called U ε method that sums the expanded uncertainty with the absolute value of the bias scaled by a factor ε assigned for a 95% distribution coverage. In addition, the alternative of using a maximum permissible error (M P E) statement—typically specified by the manufacturer of the CT instrument—to generate a rough estimate of the expanded uncertainties of CT measurements is considered. Through two examples using dimensional X-ray CT data, these possibilities are analyzed. From all the possibilities for estimation of uncertainties associated with CT dimensional measurements that are not compensated for bias, the RSSu method produced the largest uncertainty estimates and thus seems to be the most conservative approach. For dimensioning geometric features mostly ranging between 10 mm and 60 mm, the expanded uncertainties (k = 2) computed with the RSSu method ranged from 0.6 μm up to 72.7 μm. It was with the asymmetrical SUMU approach that the smaller uncertainty intervals were generated. On the other hand, uncertainty bounds estimated with the M P E based approach changed little from a constant value (around ±9.5 μm), and, therefore, risk creating significant under- or over-estimation of the uncertainty intervals. • Methods for uncertainty analysis of computed tomography (CT) metrology are reviewed. • Special attention is placed to the case of CT measurements not compensated for bias. • The root-sum-of-squares of standard uncertainties is the most conservative approach. • The asymmetrical SUMU approach produces that the smaller CT uncertainty intervals. • Uncertainty bounds estimated with the MPE-based method are of limited applicability. [ABSTRACT FROM AUTHOR]

Amplitude–wavelength (AW) maps or "Stedman diagrams" are often used to provide a graphical representation of the limitations and capabilities of surface measuring instruments. This paper presents an approach for setting the parameter constraints of X-ray computed tomography (CT) in terms of resolution and measuring range for the purpose of representing the performance of industrial CT systems on an AW map. Such AW map will allow instrument users to quickly compare the CT instrument performance to other measuring systems. Examples of the construction of AW maps for different working capabilities of X-ray CT systems, and based on experimental data, are provided. Polypropylene, aluminum, and steel are three workpiece materials considered for determining some of the limitations of measuring capability for the maps developed in this paper. Although the limiting boundaries of the AW plots presented in this paper set a generalized measure of performance for comparisons with other measuring instruments, they may evolve with more comprehensive models of the limiting factors in X-ray CT. • The measuring range and resolution limits of computed tomography (CT) are reviewed. • Experimental data is presented for determining measurement constraints of X-ray CT. • An X-ray CT instrument performance map is added to amplitude-wavelength (AW) space. • Several examples on the construction of AW maps for X-ray CT systems are provided. • AW maps facilitate comparisons of CT's competence with other measuring techniques. [ABSTRACT FROM AUTHOR]