Measurement Geometry Research Articles

Refinements for Bragg coherent X-ray diffraction imaging: electron backscatter diffraction alignment and strain field computation.

Bragg coherent X-ray diffraction imaging (BCDI) allows the 3D measurement of lattice strain along the scattering vector for specific microcrystals. If at least three linearly independent reflections are measured, the 3D variation of the full lattice strain tensor within the microcrystal can be recovered. However, this requires knowledge of the crystal orientation, which is typically attained via estimates based on crystal geometry or synchrotron microbeam Laue diffraction measurements. Presented here is an alternative method to determine the crystal orientation for BCDI measurements using electron backscatter diffraction (EBSD) to align Fe-Ni and Co-Fe alloy microcrystals on three different substrates. The orientation matrix is calculated from EBSD Euler angles and compared with the orientation determined using microbeam Laue diffraction. The average angular mismatch between the orientation matrices is less than ∼6°, which is reasonable for the search for Bragg reflections. The use of an orientation matrix derived from EBSD is demonstrated to align and measure five reflections for a single Fe-Ni microcrystal via multi-reflection BCDI. Using this data set, a refined strain field computation based on the gradient of the complex exponential of the phase is developed. This approach is shown to increase accuracy, especially in the presence of dislocations. The results demonstrate the feasibility of using EBSD to pre-align BCDI samples and the application of more efficient approaches to determine the full lattice strain tensor with greater accuracy.

The modelling of railway subgrade strengthening foundation on weak soils

Abstract As a consequence of increased axle loads and speeds of trains on modernised railway lines, there may occur problems with bearing capacity and stability of the subgrade in some sections of the railway network. This is the situation we are dealing with right now on the Polish State Railways network. Therefore, as a case study, a fragment of an existing railway embankment based on a weak foundation was chosen for the analysis of train–track–subgrade interaction. A two-stage train–track–subgrade model has been developed. The model consists of the upper part (train–track) and the lower part (subgrade-foundation). The first part is modelled as a self-contained system of differential equations which are solved by means of finite difference method and yield the stress levels on the subgrade. These stresses are treated as a load for the lower system modelled using FEM. The model has been validated using experimental data from literature, authors’ measurements, and railway staff measurements of the track geometry. Several cases of strengthening methods were calculated and compared with measurements on the railway section under consideration. Good agreement between the prediction and the measurement was found. The novelty of the model is including the heterogeneity of the subgrade, the strengthening methods, and very deep layers of its foundation as well as adding the influence of vibration on the weakening of soils. It was found that this influence is noticeable and should be included in the prediction of railway subgrade behaviour

Nominal geometry and force measures for solids and fluids

AbstractUnderstanding solid‐ and fluid‐inertia forces and their coupling with the gravity potential in complex motion scenarios is necessary for evaluating system stability and identifying root causes of system failure and accidents. Because solids and fluids have an infinite number of degrees of freedom and distributed inertia and elasticity, having meaningful qualitative and quantitative nominal measures of the kinematics and forces will contribute to a better understanding of the system dynamics. This paper proposes developing new continuum‐based nominal measures for the characterization of the oscillations and forces. By using a material‐point approach, these new nominal measures, which have their roots in the continuum‐mechanics partial‐differential equations of equilibrium and Frenet geometry, are independent of the formulation or generalized coordinates used to develop the dynamic equations of motion. The paper proposes a data‐driven‐science approach to define a nominal continuum space‐curve geometry with nominal curvature and torsion; a nominal instantaneous motion plane (IMP), which contains the resultant of all forces including the inertia forces; and a nominal instantaneous zero‐force axis (IZFA) along which the resultant of all forces vanishes. While using the material‐point approach eliminates the need for introducing moment equations associated with orientation coordinates, the IMP and IZFA concepts can be used to define the instantaneous axis of significant moment components, which can lead to accidents such as in the case of vehicle rollovers.

A machining digital twin for hybrid manufacturing

Hybrid manufacturing consisting of metal additively manufactured preforms and computer numerical control (CNC) machining has been established to be an effective method for high material use rates. However, hybrid manufacturing introduces unique challenges. Near-net shape designs are typically selected, which result in a smaller margin for part placement within the stock and stringent requirements for work coordinate system identification. Additionally, less stock material reduces the preform stiffness, which limits the material removal rates during machining. This paper demonstrates a digital twin for CNC machining of a wire arc additively manufactured preform that implements: 1) structured light scanning for stock model identification and tool path generation; 2) a fused filament fabrication apparatus to attach temporary fiducials and scan targets to the preform that enable coordinate system definition for both the CAM and CNC machine; 3) preform and tool tip frequency response function measurements to enable stable milling parameter selection; and 4) post-manufacturing measurements of geometry, surface finish, and structural dynamics to confirm designer intent. These efforts define key components of the machining digital twin for hybrid manufacturing.

Acute effects of postural changes and lower body positive and negative pressure on the eye.

Introduction: Entry into weightlessness results in a fluid shift and a loss of hydrostatic gradients. These factors are believed to affect the eye and contribute to the ocular changes that occur in space. We measured eye parameters during fluid shifts produced by lower body negative pressure (LBNP) and lower body positive pressure (LBPP) and changes in hydrostatic gradient direction (supine-prone) in normal subjects to assess the relative effects of fluid shifts and hydrostatic gradient changes on the eye. Methods: Ocular parameters (intraocular pressure (IOP), ocular geometry, and optical coherence tomography measures) were measured in the seated, supine, and prone positions. To create a fluid shift in the supine and prone positions, the lower body chamber pressure ranged from -40 mmHg to +40 mmHg. Subjects maintained each posture and LBNP/LBPP combination for 15 min prior to data collection. A linear mixed-effects model was used to determine the effects of fluid shifts (as reflected by LBNP/LBPP) and hydrostatic gradient changes (as reflected by the change from seated to supine and from seated to prone) on eye parameters. Results: Chamber pressure was positively correlated with both increased choroidal thickness (β = 0.11 p = 0.01) and IOP (β = 0.06 p < 0.001). The change in posture increased IOP compared to seated IOP (supine β = 2.1, p = 0.01, prone β = 9.5, p < 0.001 prone) but not choroidal thickness. IOP changes correlated with axial length (R = 0.72, p < 0.001). Discussion: The effects of hydrostatic gradients and fluids shifts on the eye were investigated by inducing a fluid shift in both the supine and prone postures. Both hydrostatic gradients (posture) and fluid shifts (chamber pressure) affected IOP, but only hydrostatic gradients affected axial length and aqueous depth. Changes in choroidal thickness were only significant for the fluid shifts. Changes in hydrostatic gradients can produce significant changes in both IOP and axial length. Fluid shifts are often cited as important factors in the pathophysiology of SANS, but the local loss of hydrostatic gradients in the head may also play an important role in these ocular findings.

Metric measure geometry: An approach to high-dimensional and infinite-dimensional spaces

Metric measure geometry: An approach to high-dimensional and infinite-dimensional spaces

Optimal frequency selection for accuracy improvement in binary defocusing fringe projection profilometry.

The binary defocusing fringe projection profilometry (FPP) technique has demonstrated various advantages for high-speed and high-accuracy three-dimensional (3D) surface measurement. However, higher fringe frequency does not necessarily give better measurements in binary defocusing FPP. To improve the 3D geometry measurement accuracy, this paper proposes an optimal frequency selection approach by analyzing the phase error distribution under different defocusing degrees. The phase error is analyzed theoretically based on the multi-frequency temporal phase unwrapping process, and the associated relationship with fringe frequency, system defocusing degree, noise, and other influencing factors is established. Meanwhile, optimal fringe frequency in a specific system is selected by the theoretical model combined with the validation of simulation experiments. Finally, the measurement accuracy could be effectively enhanced by the generated binary fringe patterns of optimal frequency. Both simulations and experiments verify the effectiveness and robustness of the proposed method.

Modification of correlation optimized warping method for position alignment of condition measurements of linear assets

This paper proposes a modification to a well-known alignment method, correlation optimized warping (COW), to improve the efficiency of the method and reduce the positional errors in the measurements of linear assets. The modified method relaxes the restrictions of COW in aligning the start and end of datasets and decreases the computational time. Furthermore, the method takes advantage of the interdependencies between simultaneously measured channels to overcome the missing data problem. A case study on railway track geometry measurements was conducted to implement the proposed method and assess its performance in reducing the positioning inaccuracy of the measurements. The findings revealed that the modified method could decrease the positional errors of defects to below 25 cm in 94 % of the trials.

Relationship Between Oropharyngeal Geometry and Acoustic Parameters in Singers: A Preliminary Study

To verify possible correlations between formant and cepstral parameters and oropharyngeal geometry in singers, stratified by sex. Voice records and oropharyngeal measures of 31 singers - 13 females and 18 males, mean age of 28 (±5.0) years - were retrieved from a database and analyzed. The oropharyngeal geometry measures were collected with acoustic pharyngometry, and the voice records consisted of sustained vowel /Ԑ/ phonation, which were exported to Praat software and edited to obtain the formant and cepstral parameters, stratified by sex. The Pearson linear correlation test was applied to relate voice parameters to oropharyngeal geometry, at the 5% significance level; the linear regression test was used to justify the variable related to the second formant. Differences between the sexes were identified only in the oral cavity length (greater in males) and pharyngeal cavity length (greater in females). There was a linear correlation between the third formant and the cepstrum in the female group. In the male group, there was a linear correlation between the cepstrum and the third and fourth formants. A positive linear correlation with up to 95% confidence was also identified between the pharyngeal cavity volume and the second formant in the female group, making it possible to estimate a regression model for the second formant (R2=0.70). There are correlations between the oropharyngeal geometry and formant and cepstral parameters in relation to sex. The pharyngeal cavity volume showed the greatest correlation between females and the second formant.

Automated geometry measurement and deep rolling of butt welds

During the joining of two metal sheets by welding, a process-specific geometry of the weld is created. The local geometry of the created weld has a decisive influence on its fatigue strength. This is due to stress concentration at the geometric notches. In this paper, a process known from mechanical engineering called deep rolling is applied on butt welds. The influence on the local weld geometry and the local stress concentration after deep rolling is investigated. Additionally, a novel automated measurement system using optical laser line scanning is presented. The system is qualified for the evaluation of the local weld geometry regarding its flank angles and toe radii. The presented investigations show that the deep rolling process influences the stress concentrations determined by 2D-FE-simulations using real scan data. A correlation between the difference in toe radii or local notch stresses before and after deep rolling and the initial flank angle was found. This indicates that there are process and geometry specific conditions for the successful application of the deep rolling process.

Disc geometry measurement methods affect reported compressive mechanics by up to 65.

Mechanical testing is a valuable tool for assessing intervertebral disc health, but the wide range of testing protocols makes it difficult to compare results from different studies. Normalizing mechanical properties by disc geometry allows for such comparisons, but there is little consistency in the methods by which disc geometry is measured. As such, we hypothesized that methods used to measure disc geometry would impact reported mechanical properties. Disc height and area were measured using computed tomography (CT), digital calipers, and ImageJ to yield three different measurements for disc height and six for disc area. Disc heights measured by digital calipers ex situ were >30% less than disc heights measured in situ by CT, and disc areas measured ex situ using ImageJ were >30% larger than those measured by CT. This significantly affected reported mechanical properties, leading to a 65% reduction in normalized compressive stiffness in the most extreme case. Though we cannot quantitatively correct between methods, results presented in this study suggest that disc geometry measurement methods have a significant impact on normalized mechanical properties and should be accounted for when comparing results.

Data‐driven maintenance planning and scheduling based on predicted railway track condition

AbstractTimely planning and scheduling of railway infrastructure maintenance interventions are crucial for increased safety, improved availability, and reduced cost. We propose a data‐driven decision‐support framework integrating track condition predictions with tactical maintenance planning and operational scheduling. The framework acknowledges prediction uncertainties by using a Wiener process‐based prediction model at the tactical level. We also develop planning and scheduling algorithms at the operational level. One algorithm focuses on cost‐optimisation, and one algorithm considers the multi‐component characteristics of the railway track by grouping track segments near each other for one maintenance activity. The proposed framework's performance is evaluated using track geometry measurement data from a 34 km railway section in northern Sweden, focusing on the tamping maintenance action. We analyse maintenance costs and demonstrate potential efficiency increases by applying the decision‐support framework.

Path Loss Prediction Model for Propagating Radio Wave in Woodland

This paper presents new empirical prediction models for loss estimation in forest environment. Experimental investigations were carried out on groups of trees in form of woodland and lines of trees at SHF band under different operational contexts. In the experimentations, two major measurement geometries (propagation “into” and propagation “inside” forest) were adopted on site to site basis. Results from all the sites displayed a common trend, in that they all showed a persistent decay in signal power with the depth of vegetation and which is dependent on the measurement geometries.&#x0D; Using a “Power Law” theory, a new empirical loss prediction model has been proposed for each propagation scenario using parametric equations which are in line with the general formulations of the ITU-R models. These new models were tested with the standard empirical loss prediction models and gave a statistical adherence with the fitted ITU-R model.&#x0D; It is anticipated that these new models will address the inadequacy in the existing prediction models which have not taken cognizance of the differences in operational contexts of each propagation scenario in their formulations.

Pose Estimation and Damage Characterization of Turbine Blades during Inspection Cycles and Component-Protective Disassembly Processes.

Inspection in confined spaces and difficult-to-access machines is a challenging quality assurance task and particularly difficult to quantify and automate. Using the example of aero engine inspection, an approach for the high-precision inspection of movable turbine blades in confined spaces will be demonstrated. To assess the condition and damages of turbine blades, a borescopic inspection approach in which the pose of the turbine blades is estimated on the basis of measured point clouds is presented. By means of a feature extraction approach, film-cooling holes are identified and used to pre-align the measured point clouds to a reference geometry. Based on the segmented features of the measurement and reference geometry a RANSAC-based feature matching is applied, and a multi-stage registration process is performed. Subsequently, an initial damage assessment of the turbine blades is derived, and engine disassembly decisions can be assisted by metric geometry deviations. During engine disassembly, the blade root is exposed to high disassembly forces, which can damage the blade root and is crucial for possible repair. To check for dismantling damage, a fast inspection of the blade root is executed using the borescopic sensor.

Overview of methods for determining the depth distribution of elements in X-ray fluorescence analysis

X-ray fluorescence analysis is a frequently used analytical method in a number of areas for many decades, including the research of objects of cultural heritage. Especially in this area, the irreplaceable advantage is the fact that the measurement can be performed non-destructively and non-invasively on the examined object as a whole. It affects only a relatively thin layer at the surface of the object under investigation, nevertheless, this layer can have a complex structure (various coatings, gilding or other metallization, paint layers, etc.). Information about it can be a valuable contribution both to historical knowledge and to restoration work. During the development of the method, therefore, several procedures were elaborated to estimate the homogeneity or possible inhomogeneities of the investigated layer. In principle, the simplest one is to measure at different beam angles. However, this also changes the depth in the material into which the radiation penetrates. Without changing the measurement geometry, it is possible to use simultaneous detection of two different energy lines of the characteristic radiation of the investigated element (e.g., Kα and Kβ) and to evaluate the depth distribution on the basis of their ratio. Finally, the most sophisticated, but also the most informative, is the confocal arrangement of the spectrometer, where the focus, i.e. the intersection of the beams of incident and emitted radiation very narrowly collimated by the capillary optics, shifts to the depth of the measured material. This review paper summarizes the principles and possibilities of these methods, their advantages and limitations, and thus gives information for their use for specific needs. The use is illustrated by examples of specific measurements of art objects, realized in various laboratories, but especially in the laboratory of the authors of this paper.

An Improved Point Cloud Upsampling Algorithm for X-ray Diffraction on Thermal Coatings of Aeroengine Blades

X-ray diffraction can non-destructively reveal microstructure information, including stress distribution on thermal coatings of aeroengine blades. In order to accurately pinpoint the detection position and precisely set the measurement geometry, a 3D camera is adopted to obtain the point cloud data on the blade surface and perform on-site modeling. Due to hardware limitations, the resolution of raw point clouds is insufficient. The point cloud needs to be upsampled. However, the current upsampling algorithm is greatly affected by noise and it is easy to generate too many outliers, which affects the quality of the generated point cloud. In this paper, a generative adversarial point cloud upsampling model is designed, which achieves better noise immunity by introducing dense graph convolution blocks in the discriminator. Additionally, filters are used to further process the noisy data before using the deep learning model. An evaluation of the network and a demonstration of the experiment show the effectivity of the new algorithm.

Accuracy assessment of light detection and ranging system measurements for jointed concrete pavement surface geometry

ABSTRACT Stationary Light Detection and Ranging (LiDAR) systems provide detailed three-dimensional (3D) point clouds for pavement surface geometry measurements. Despite their long presence in the market, LiDAR systems are still relatively new to pavement engineers and there are only few studies verifying their accuracy. To bridge this gap, laboratory and field tests were performed to investigate the accuracy of LiDAR instrument. In the laboratory test, a wooden board was set up and a dial indicator was used to measure deflections when loads were applied. The magnitudes were compared with the deflections from LiDAR scans estimated by a low-order polynomial fit model and a thin-plate spline (TPS) fit model. In the field test, profiles were acquired for concrete pavement using a standard profilometer and the LiDAR system. Agreement among these profiles was investigated. Test results assured that this stationary LiDAR system could provide acceptable accuracy and precision for slab surface geometry measurements.

In-situ ultrasonic monitoring for Vat Photopolymerization

Vat Photopolymerization (VPP) additive manufacturing processes employ photopolymerization reactions to crosslink monomers layer by layer under light exposure schemes corresponding to the cross-sections of a target object. Such processes have been widely used in various applications, from rapid prototyping to biomedical implants, soft robotics, and flexible electronics. In-situ process monitoring is critical for process optimization and control to achieve precise structures and desired properties via VPP. As existing research focuses on the online measurement of part geometry, there lack in-situ monitoring technologies to obtain real-time information about the curing and mechanical properties of VPP printed parts, especially the degree of conversion (DoC) that greatly affects the mechanical properties of as-printed and finished parts. This work demonstrates for the first time, an in-situ ultrasonic monitoring (IUM) method, developed based on ultrasonic testing methods for DLP process monitoring. The developed method is simplistic, rapid, versatile, cost-effective, and non-invasive compared to the state-of-the-art methods such as in-situ Fourier-Transform Infrared Spectroscopy and Atomic Force Microscopy that are adapted to monitor VPP. An IUM framework with specific data analytics methods is developed to process the real-time acquired ultrasonic signal for evaluating the evolving Young’s modulus and DoC of the as-printed part during VPP. An experimental study is performed to exemplify that the developed IUM method can vividly reveal the process dynamics under different exposure intensities and probe the part properties evolution with adequate sensitivity and accuracy. This novel IUM method will offer unique insights into process dynamics and process-property relationships for VPP processes modeling and real-time feedback control, facilitating 3D and 4D printing of sophisticated products such as soft robots that require localized manipulation of mechanical properties.

Long-distance polarizing microscope system combined with solenoid-type magnet for microscopy and simultaneous measurement of physical parameters.

We have developed a long-distance polarizing microscope system combined with a solenoid-type superconducting magnet. By inserting an infinity-corrected objective lens into the magnet, direct or polarizing microscope images are observed in magnetic fields of up to 12T at various temperatures down to 2K. Through magneto-optical measurements in the transmission geometry, the local magnetization process of a transparent magnet is evaluated in areas of 10 × 10 µm2. This system enables simultaneous measurements of other physical properties over a wide range of temperatures and magnetic fields. The basic principle of the proposed long-distance microscopy can be applied to imaging experiments in various research fields, particularly biology and chemistry.

An Automated Rail Extraction Framework for Low-Density LiDAR Data Without Sensor Configuration Information

Around one-third of the U.S. rail network is owned and operated by shortlines (Class II and III railroads). The infrastructure conditions of these railroads are marginal, and their revenue and number of employees are insufficient. To conduct proper and timely infrastructure management, it is critical for shortlines to establish a reliable and cost-effective inventory of their existing rail tracks. Significant efforts have been made to develop and employ automatic rail extraction methods as it is a critical step to establishing a rail infrastructure inventory. However, existing methods rely heavily on high-density point cloud datasets with known sensor properties and configurations or sophisticated imaging sensors. These requirements prevent their deployments in shortlines because point cloud data available to shortlines are often in low-density and with unknown specifications constrained by their financial situations. To address those limitations, we propose an automatic, configuration-independent coarse-to-fine extraction method for low-density LiDAR data. The proposed extraction framework is only developed based on high-level geometric features of the rail that can even be captured by low-density point cloud data with unknown sensor properties and configurations. The proposed method is evaluated on the existing grade-crossing dataset collected by the Federal Railroad Administration for grade-crossing safety evaluation with a point cloud density of only 293 points/<inline-formula> <tex-math notation="LaTeX">$\text{m}^{{2}}$ </tex-math></inline-formula>. The overall performance shows average completeness of 96.97&#x0025;, correctness of 99.71&#x0025;, and quality of 96.67&#x0025; for all extraction scenarios. The promising results provide shortlines a capability to extract rails for any geometry measurements based on any low-density LiDAR data available to them.