Optical 3D Measurement Research Articles

Fire-Induced Failure of Long-Term Service and Fresh Concrete Beams Subjected to Fire

In engineering, reinforced concrete beams are subjected to natural erosion and the working stress state. However, previous studies regarding structural fire have focused on new concrete beams, and most results are obtained from no-stress-state tests. Hence, research that considers the natural erosion and working stress states of beam members in fire is lacking. In this study, fire experiments were performed to investigate the differences between long-term service concrete beams and new elements under loads. A technique using ARAMIS three-dimensional (3D) optical strain measurement was adopted; it provides increased sample throughput and 3D measurements that indicate the change in strain more intuitively. Results show that the moisture content of concrete determines the spalling degree of concrete under the influence of working stress. With the increase of concrete moisture content, the range of temperature of heated and backfire surface increases and the spalling phenomenon is more obvious, especially when the moisture content exceeds 2.5%. In addition, the long-term service specimens are affected by fire more easily, thereby accelerating the destruction process owing to the degree of carbonation.

EVALUATION OF INTERIOR ORIENTATION MODELLING FOR CAMERAS WITH ASPHERIC LENSES AND IMAGE PRE-PROCESSING WITH SPECIAL EMPHASIS TO SFM RECONSTRUCTION

Abstract. For optical 3D measurements in close-range and UAV applications, the modelling of interior orientation is of superior importance in order to subsequently allow for high precision and accuracy in geometric 3D reconstruction. Nowadays, modern camera systems are often used for optical 3D measurements due to UAV payloads and economic purposes. They are constructed of aspheric and spherical lens combinations and include image pre-processing like low-pass filtering or internal distortion corrections that may lead to effects in image space not being considered with the standard interior orientation models. With a variety of structure-from-motion (SfM) data sets, four typical systematic patterns of residuals could be observed. These investigations focus on the evaluation of interior orientation modelling with respect to minimising systematics given in image space after bundle adjustment. The influences are evaluated with respect to interior and exterior orientation parameter changes and their correlations as well as the impact in object space. With the variety of data sets, camera/lens/platform configurations and pre-processing influences, these investigations indicate a number of different behaviours. Some specific advices in the usage of extended interior orientation models, like Fourier series, could be derived for a selection of the data sets. Significant reductions of image space systematics are achieved. Even though increasing standard deviations and correlations for the interior orientation parameters are a consequence, improvements in object space precision and image space reliability could be reached.

A Comparative Analysis on Organic and Inorganic Core Binders for a Gravity Diecasting Al Alloy Component

The last two decades have seen a growing trend toward the use of inorganic binders in core making for the metalcasting field. Despite the health and environmental benefits of the inorganic binders, wider commercial use requires ongoing technical improvements to address some potential inherent limitations of this technology. Considering that inorganic cores can suffer from storage stability, this study sets out to check whether inorganic core binders are fit to replace organic ones in producing a gravity diecasting Al alloy component. First, the humidity resistance of both organic and inorganic sand cores, within a typical time-frame storage in the foundry, was evaluated by moisture absorption tests. Then, 3D optical measurements were performed to assess the relative dimensional changes of inorganic cores. Last, the influence of the core system was analyzed through microstructural and mechanical investigations on castings manufactured by using organic and inorganic binders. The experimental findings have shown that the moisture absorption during storage in the foundry warehouse, which lasted up to 14 days, was not enough to jeopardize the functionality of the cores. Furthermore, the tensile and microstructural outcomes revealed that inorganic cores could comply with both high component design requirements and even more stringent environmental regulations of foundries.

AUTOMATIC ANTHROPOLOGICAL LANDMARKS RECOGNITION AND MEASUREMENTS

Abstract. Many anthropological researches require identification and measurement of craniometric and cephalometric landmarks which provide valuable information about the shape of a head. This information is necessary for morphometric analysis, face approximation, craniafacial identification etc. Traditional techniques use special anthropological tools to perform required measurements, identification of landmarks usually being made by an expert-anthropologist. Modern techniques of optical 3D measurements such as photogrammetry, computer tomography, laser 3D scanning provide new possibilities for acquiring accurate 2D and 3D data of high resolution, thus creating new conditions for anthropological data analysis. Traditional anthropological manual point measurements can be substituted by analysis of accurate textured 3D models, which allow to retrieve more information about studied object and easily to share data for independent analysis. The paper presents the deep learning technique for anthropological landmarks identification and accurate 3D measurements. Photogrammetric methods and their practical implementation in the automatic system for accurate digital 3D reconstruction of anthropological objects are described.

Period-Wise Phase Unwrapping Method With Two Gray Level Coding Patterns

Fringe projection profilometry is a widely used three-dimensional (3D) optical measurement technique. However, it is quite challenging to quickly obtain the 3D information of objects. Minimizing the number of patterns for phase unwrapping is an efficient way to address the above problem, and many methods have been proposed. This paper reports a period-wise phase unwrapping method with only two gray level coding patterns. Due to a hybrid coding strategy implemented, the number of patterns used in the proposed method reduces by one in comparison with conventional gray level method when generating the same number of codewords. A robust decoding scheme is also developed to determine the fringe order, and its accuracy is guaranteed by using the self-correcting method to remove the phase errors. Some experiments have been conducted, and their results confirm that the success of the proposed method.

Single column plate plus other column lag screw fixation vs. both column plate fixation for anterior column with posterior hemitransverse acetabular fractures - a biomechanical analysis using different loading protocols.

Open reduction and internal fixation of both columns is considered the treatment of choice for displaced anterior column with posterior hemitransverse (ACPHT) fractures in non-geriatric patients. Plate fixation of one column combined with lag screw fixation of the other column allows to decrease operative time and approach-related morbidity compared to conventional both column plating. The aim of this biomechanical study was to evaluate whether single column plate plus other column lag screw fixation confers similar stability to both column plate fixation. Physiological loads were simulated using both the single-leg stance (SLS) as well as the sit-to-stand (STS) loading protocols. A clinically relevant ACPHT fracture model was created using fourth-generation composite hemipelves. Fractures were stabilized with three different fixation constructs: (1) anterior column plate plus posterior column screw fixation (AP+PCS), posterior column plate plus anterior column screw fixation (PP+ACS) and anterior column plate plus posterior column plate fixation (AP+PP). Specimens were loaded from 50 to 750N with a ramp of 100N/s. Fracture gap motion (FGM) and relative interfragmentary rotation (RIFR) between the three main fracture fragments were assessed under loads of 750N using an optical 3D measurement system. STS loading generally resulted in higher mean FGM and RIFR than STS loading in the AP+PCS and AP+PP groups, while no significant differences were found in the PP+ACS group. Compared to conventional both column plate fixation (AP+PP), PP+ACS displayed significantly higher FGM and RIFR between the iliac wing and the posterior column during SLS loading. No significant differences in FGM and RIFR were identified between the AP+PCS and the AP+PP group. Overall, single column plate plus other column lag screw fixation conferred similar stability to conventional both column plate fixation. From a clinical point of view, AP+PCS appears to be the most attractive alternative to conventional AP+PP for internal fixation of ACPHT fractures.

Experimental Comparison of Optical Inline 3D Measurement and Inspection Systems

Fast optical 3D inline inspection sensors are a powerful tool to advance factory automation. Many of these visual inspection tasks require high speeds, high resolutions, and repeatability. Stereo vision, photometric stereo, light sectioning, and structured light are the most common principles for inline imaging in the several micrometers to sub-millimeter resolution range. Selecting the correct sensor principle can be challenging as manufacturers’ datasheets frequently use different values to describe their systems and do not stick to proposed characterizations defined by the “Initiative Fair Data Sheet” or the VDE/VDI standards. With the help of standardized parameters, this paper aims to compare four different measurement principles, namely AIT’s own single sensor light field camera method, a structured light pattern projector, a laser triangulation sensor, and a stereo camera system, with an approximate field of view of $100\times 100$ mm. We demonstrate simple yet meaningful experiments to determine lateral resolution, temporal noise, and calibration accuracy to enable an objective system comparison. Additionally, the reproduction of small surface structures and an overall performance on a challenging test object is evaluated. Results show that the measurement principles partly serve different application areas. The provided methods will help end users to select the correct sensor for specific applications.

The crack surface morphology investigation of S355J2 steel after bending-torsion fatigue

The paper describes the analysis of crack surface morphology of S355J2 steel specimens after bending-torsion fatigue. These experimental investigations of the surface topography were carried out using the focus variation microscope, an optical 3D measurement device. Selected results of measured fracture surfaces for S355J2 steel were analysed according to the surface texture ISO 25178 standard. Differences in roughness values for different loadings were demonstrated. For profile Rx and areal Sx parameters, characteristic relationships of fracture zones have been demonstrated. It has been shown that roughness profile Ra for the rupture area is higher than for the propagation area, as well as increases after both the LCF and HCF tests and increases with the torsional loading level. However, Sa in the propagation area increases and the rupture area decreases.

Basic knowledge of 3D optical measurement methods used for intraoral scanners

Basic knowledge of 3D optical measurement methods used for intraoral scanners

Application of window-optimized 2D S-transform in the optical 3D shape measurement

Combing the merits of windowed Fourier transform and wavelet transform, 2D S-transform has been a popular method in optical 3D measurement. As an improvement of 1D S-transform, 2D S-transform has better features to reduce noises and non-linearity because it can analyze the whole fringe patterns in two directions. However, the window size of traditional 2D S-transform is related to local frequency of tested objects, therefore traditional 2D S-transform can not get accurate surface information when the tested surface is complicated. To overcome the problem, a window-optimized 2D S-transform with theory analysis and mathematical derivation is proposed with two parameters to control the width of Gauss window. Simulation verifies that the proposed method can extract more accurate wrapped phase. At last, simulation and experiments are carried out to show that the proposed method can get more accurate measurement results when the tested surface is complicated.

Perspective Camera Model With Refraction Correction for Optical Velocimetry Measurements in Complex Geometries.

Camera calibration is among the most challenging aspects of the investigation of fluid flows around complex transparent geometries, due to the optical distortions caused by the refraction of the lines-of-sight at the solid/fluid interfaces. This work presents a camera model which exploits the pinhole-camera approximation and represents the refraction of the lines-of-sight directly via Snell's law. The model is based on the computation of the optical ray distortion in the 3D scene and dewarping of the object points to be projected. The present procedure is shown to offer a faster convergence rate and greater robustness than other similar methods available in the literature. Issues inherent to estimation of the refractive extrinsic and intrinsic parameters are discussed and feasible calibration approaches are proposed. The effects of image noise, volume size of the control point grid and number of cameras on the calibration procedure are analyzed. Finally, an application of the camera model to the 3D optical velocimetry measurements of thermal convection inside a polymethylmethacrylate (PMMA) cylinder immersed in water is presented. A specific calibration procedure is designed for such a challenging experiment where the cylinder interior is not physically accessible and its effectiveness is demonstrated by providing velocity field reconstructions.

Evaluation of tensile strength of painted steel wi local corrosion at structural connections

Steel structures are often protected by paint coating, but the coating easily deteriorates at structural connections because moisture and dust accumulate at the contact. This leads to the local corrosion on the steel members near the contact and a reduction in tensile performance. The corrosion characteristics and tensile strength of steel plates with a concrete block are investigated. Four types of specimens were prepared, and each type had an unpainted area with different lengths away from the contact boundary. An accelerated cyclic corrosion test was conducted for 600 cycles using CCT-I test conditions specified in the ASTM D 6899–03 standard. To analyze the corrosion characteristics, the surface geometry of corroded specimens was measured in 1 mm × 1 mm intervals by an optical 3D measurement system. The average corrosion depth outside the concrete block was proportional to the unpainted area, and the average corrosion depth inside the concrete block was accelerated in unpainted areas. The two average corrosion depths have a power regression relationship, so the average corrosion depth inside the concrete block can be estimated from the average corrosion depth outside it. A simple method for quantitatively defining the residual thickness is proposed in terms of the effective thickness and the residual tensile strength, which can be evaluated using the effective thickness. Compared to previously proposed methods for this purpose, the effective thickness has higher accuracy.

Combining laser transformation hardening and ultrasonic impact strain hardening for enhanced wear resistance of AISI 1045 steel

A medium-carbon steel AISI 1045 was hardened by a laser heat treatment (LHT), a multi-pin ultrasonic impact treatment (UIT), and two combined laser-ultrasonic surface treatments (UIT + LHT and LHT + UIT processes) to improve the wear resistance of the surface layer. The paper is focused on detecting the relationship between the surface roughness and microstructure, phase state, hardness, residual stress of the specimens hardened by the LHT, UIT and combined UI + LHT/LHT + UIT processes, and their wear and friction behaviors. The hardened plane specimens were examined after the short-term (15 min) and long-term (45 min) wear tests under oil-lubricated conditions in the quasi-static and dynamic loads. The analysis of the surface morphologies and cross-section profiles of the worn tracks were assessed by an optical 3D measurement system and scanning electron microscopy (SEM). The wear mechanisms are also discussed. Results showed that the combined LHT + UIT treatment provides a lower surface roughness (Ra ~0.25 μm) and a highest surface hardness (~11,000 HV0.05) while the combined UIT + LHT treatment leads to the deeper hardened zone by 1.5–2 times. As compared to the untreated specimen (dynamic tests), the wear loss magnitudes were respectively decreased by ~5%, 35%, 42%, and 84% after the UIT, LHT, combined UIT + LHT and LHT + UIT processes. The LHT + UIT-processed specimen has the highest wear resistance owing to the formation of the fine-grained martensitic microstructure, more flattened surface microrelief, and the absence of the oxide film.

High-resolution real-time 360∘ 3D surface defect inspection with fringe projection profilometry

Since a slight variance in production processes can make the entire production run defective, defect inspections are indispensable procedures in manufacturing processes to ensure high quality of each item before entering the next manufacturing step. Three-dimensional (3D) optical shape measurement technologies are widely applied for surface defect inspection of complex workpieces because of its high-accuracy and digitization. However, the complex surface structure and position of the test object can pose serious challenges, making inspections still relatively slow, expensive, and complicated in implementation and maintenance. In this work, we propose a real-time 360∘ 3D surface defect inspection approach based on fringe projection profilometry without any auxiliary equipment for position control. Firstly, a multi-view 3D measurement based on geometric constraints is employed to acquire high-accuracy depth information from different perspectives. Then, a cycle-positioning-based registration scheme with the establishment of the pose-information-matched 3D standard digital model is proposed to realize rapid alignment of the measured point cloud and the standard model. Finally, a minimum 3D distance search is driven by a dual-thread processing mechanism for simultaneous scanning and detecting to quantify and locate 3D surface defects in real time. Experimental results show that our method can accurately identify the surface defects of complicated objects in real time in an extremely simple (hand-held) manner, saving a lot of operational expenses on precision alignment and position-orientation adjustment. The proposed method holds tremendous potential for quality control in many facets of industry, such as product development, testing, and manufacturing.

Characterization of a duplex coating (boriding + sputter-deposited AlCrON) synthesized on an ASTM F-75 cobalt alloy

Metallic biomaterials have been widely used due to their excellent mechanical properties. Cobalt-chromium-molybdenum alloys, in particular are among the safest for the fabrication of orthopedic prostheses. Nevertheless, the liberation of metallic ions as a result of wear has become a problem due to adverse biological reactions. Thus, surface modification through thermochemical treatments and ceramic coatings may be used to improve the tribological properties of the alloy. In this work, a duplex coating obtained from a boriding thermochemical treatment plus an aluminum-chromium oxynitride coating created by physical vapor deposition was synthesized on an ASTM F-75 cobalt alloy. This surface condition was compared with a borided and an untreated ASTM F-75 cobalt alloy. Surfaces were characterized using scanning electron microscopy (SEM) with energy dispersive spectroscopy, X-ray diffraction, and nanoindentation test. The tribological response was studied by means of a ball-on-disc tribometer under dry-sliding conditions tracking the coefficient of friction, volume loss, wear rate, and surface damage by stereoscopy, profilometry, optical 3D measurements, and SEM. Duplex coating increased the wear resistance 7 times relative to the wear resistance of the untreated sample, and 1.5 times relative to the borided sample.

Precisely Controlled Two-Dimensional Rhombic Copolymer Micelles for Sensitive Flexible Tunneling Devices

Nanoscale two-dimensional (2D) organic materials have attracted significant interest on account of their unique properties, which result from their ultrathin and flat morphology. Supramolecular 2D ...

MACHINE LEARNING FOR APPROXIMATING UNKNOWN FACE

Abstract. The problem of facial appearance reconstruction (or facial approximation) basing on a skull is very important as for anthropology and archaeology as for forensics. Recent progress in optical 3D measurements allowed to substitute manual facial reconstruction techniques with computer-aided ones based on digital skull 3D models. Growing amount of data and developing methods for data processing provide a background for creating fully automated technique of face approximation.The performed study addressed to a problem of facial approximation based on skull digital 3D model with deep learning techniques. The skull 3D models used for appearance reconstruction are generated by the original photogrammetric system in automated mode. These 3D models are then used as input for the algorithm for face appearance reconstruction. The paper presents a deep learning approach for facial approximation basing on a skull. It exploits the generative adversarial learning for transition data from one modality (skull) to another modality (face) using digital skull 3D models and face 3D models. A special dataset containing skull 3D models and face 3D models has been collected and adapted for convolutional neural network training and testing. Evaluation results on testing part of the dataset demonstrates high potential of the developed approach in facial approximation.

Biomechanical comparison of fixation techniques for transverse acetabular fractures – Single-leg stance vs. sit-to-stand loading

ObjectivesTo biomechanically compare five different fixation techniques for transverse acetabular fractures using both the single-leg stance (SLS) and the sit-to-stand (STS) loading protocols and to directly compare fracture gap motion (FGM) and relative interfragmentary rotation (RIFR). MethodsTranstectal transverse acetabular fractures were created on fourth-generation composite hemipelves in a reproducible manner. Five different fixation techniques were biomechanically assessed using both an SLS and STS loading protocol: anterior plate (AP) only, posterior plate (PP) only, anterior plate plus posterior column screw (AP+PCS), posterior plate plus anterior column screw (PP+ACS) and anterior plus posterior plate (AP+PP). After preconditioning, the specimens were loaded from 50 to 750 N with a ramp of 100 N/s. FGM and RIFR under loads of 750 N were measured using an optical 3D measurement system. ResultsIn the three groups of fixation techniques addressing both columns, STS loading resulted in higher mean FGM and in RIFR than SLS loading. No construct failure was observed. In the single plate groups (AP only and PP only), STS loading resulted in failure of all specimens before reaching loads of 750 N, while no failure occurred after SLS loading. No significant differences in FGM and RIFR were found between the double plate (AP+PP) and the single plate plus column screw (AP+PCS and PP+ACS) techniques. ConclusionSLS loading appeared to overestimate the strength of acetabular fracture fixation constructs and STS loading may be more appropriate to provide clinically relevant biomechanical data. Internal fixation of a single column might not provide adequate stability for transverse fractures, while strength of single plate plus column screw fixation and double plate fixation was comparable.

Large-scale structured light 3D shape measurement with reverse photography

Combining the advantages of structured light and close range photogrammetry is an effective strategy for large-scale three-dimensional (3D) optical shape measurement. Several coded targets are typically required to be pasted on the object being tested, which induces several shortcomings. This paper proposes a structured light measurement technique based on reverse photography. An auxiliary reverse camera is installed behind the structured light system. When a single local measurement is performed, the reverse camera observes a large liquid crystal display (LCD) screen that is used as an oriented phase target. According to the multiple imaging constraints for the reverse camera, the local 3D shape data of multi-view structured light measurements are unified in a global frame defined on the LCD screen, achieving a holistic 3D shape data fusion. The proposed method possesses the advantage of reverse information transmission and pose transfer, achieving non-contact large-scale 3D shape measurement.

Geometry constrained correlation adjustment for stereo reconstruction in 3D optical deformation measurements.

Recovering the geometric shape of deformable objects from images is essential to optical three-dimensional (3D) deformation measurements and is also actively pursued by researchers. Most of the existing techniques retrieve the shape data with triangulation based on pre-estimated stereo correspondences. In this paper, we instead propose to recover depth information directly from images of a binocular vision system for 3D deformation estimation. Given a calibrated geometry of the system, the reprojection error is parameterized by the depth and then described with local intensity dissimilarity between a stereo pair in considering spatial deformation. Afterward, a correlation adjustment model is formulated to estimate the depth parameter by minimizing the error. As a solving strategy, we show the Gauss-Newton linearization of the proposed model and its initialization. 3D displacement estimation based on depth information is also presented. Experiments, including rigid translation and bending deformation measurements, are conducted to verify the performance of the proposed method. Results show that the proposed method is accurate yet precise in 3D deformation estimations. Other underlying developments are underway.