Optical Digital Image Research Articles

Etching Method to create a Random Speckle Pattern on Semi-Solid Cast A356 Aluminium for DIC in-situ strain measurements

Aluminum semi-solid casting is constantly evolving, as it offers a combination of reduced shrinkage porosity and gas entrapment defects together with high productivity and an extended die-life. The relationship between the microstructure and stress-strain behavior is not well-understood due to its non-conventional microstructure. In-situ tensile testing, combined with optical microscope and Digital Image Correlation (DIC), has been used for local strain distribution measuements in cast irons. The critical capability was an etching technique to generate a micro-scale random speckle pattern with a sufficiently high speckle density to enable the sufficient spatial resolution of displacement and strain. The current paper focuses on the development of a pit etching procedure for the semi-solid cast A356 aluminum alloy to study local strain accommodation on the microstructure during tensile loading. The critical challenge of this procedure was the generation of homogeneously distributed pits on both the primary aluminum and eutectic regions. Therefore, a heated solution used for wet-etch aluminum in microfabrication was modified as well as a process adapted to generate pits with suitable characteristics. In-situ tensile tests were performed attached to an optical microscope to record the microstructure and displacements during loading. DIC software was used for analysis. The procedure was validated through a comparison between the resulting Young´s moduls using standard tensile testing and the DIC process on the speckle pattern generated. A good fit between the two methods for Young´s modulus was found. The spatial resolution obtained was, however, not sufficient to fully resolve the strain gradients in the microstructure, but it did reveal large strain variations in the microstructure.

High temperature Gleeble microtensile testing of metallic micro specimens

Abstract Engineering of micro parts is an increasingly important area of industrial activity and this field is rapidly developing further. Thus, the simulation of micro parts also becomes more and more important. As reliable material data is required to obtain accurate simulation results, test setups are also necessary to determine the material properties. An experimental setup for microtensile testing of stainless steel micro specimen (i. e., specimen with at least one dimension below 1 mm) to obtain material data in the temperature range from 20 to 350 °C is presented herein. Heating of the specimen is based on Joule (resistive) heating as it is done in macroscopic testing in Gleeble machines. Contactless measurement of temperatures is conducted by an infrared (IR) camera and the determination of strain by a combination of optical microscopy and digital image correlation (DIC). First samples were made from the stainless steel 17-4PH and the results obtained are presented and discussed in comparison with macroscopic properties of this material.

Characterization of re-grown floc size and structure: effect of mixing conditions during floc growth, breakage and re-growth process

The impact of mixing speed in three stages-before breakage, during breakage, and after breakage-on re-grown floc properties was investigated by using a non-intrusive optical sampling and digital image analysis technique, respectively. And then, on the basis of different influence extent of mixing speed during each stage on size and structure of re-grown flocs, coagulation performance with varying mixing speed was analyzed. The results indicated that the broken flocs could not re-grow to the size before breakage in all cases. Furthermore, increasing mixing intensity contributed to the re-formation of smaller flocs with higher degree of compactness. For slow mixing before breakage, an increase in mixing speed had less influence on re-grown floc properties due to the same breakage strength during breakage, resulting in inconspicuous variation of coagulation efficiency. For rapid mixing during breakage, larger mixing speed markedly decreased the coagulation efficiency. This could be attributed that mixing speed during breakage generated greater influence on re-grown floc size. However, as slow mixing after breakage was elevated, the coagulation efficiency presented significant rise, indicating that slow mixing after breakage had more influence on re-grown floc structure upon re-structuring and re-arrangement mechanism.

New algorithms for verifying the consistency between satellite images and survey conditions

This paper is concerned with the problem of verifying the consistency of the Earth remote sensing data, including digital optical images and survey parameters metadata. The solution of the problem is based on analysis of specific numerical characteristics of the image that depend directly on the survey parameters, such as position of the Sun, position of the spacecraft, and orientation of the recorder. This paper presents two fully automatic calculation procedures (algorithms) of performing such analysis and making a decision about mutual consistency or inconsistency of the data.

Large Strain and Small-Scale Biaxial Testing of Sheet Metals

Small-scale and multi-axial testing of sheet metals, particularly of lightweight alloys and advanced steels are becoming important as these materials exhibit forming behavior sensitive to their unique microstructural features and strain paths. As an alternative to large-scale standard tests, in this paper we introduce a novel biaxial tensile test apparatus utilizing miniature cruciform samples. The compact and portable apparatus includes a custom-built optical microscope and high-resolution digital image correlation (DIC) equipment for in-plane and in-situ strain measurements at the microstructure scale. The small strain and premature fracture problems common to the cruciform tests are solved by optimizing the sample design and by meticulously controlling the manufacturing steps and surface finish. Strain analyses reveal a key mechanism responsible for large strains and fracture at the center. This mechanism suppresses the local neck formation and allows uniform deformation under equibiaxial conditions until fracture. When normalized with the strain hardening exponent of the sample material (Al 6061-T6), the effective strain value before fracture, $$ \overline{\varepsilon}/n \sim 3 $$ , surpass the reported values for similar materials tested by cruciform and standard methods.

Research on realizing the 3D occlusion tracking location method of fish's school target

This paper takes the water detection and warning system as the application background, and studies on the school of fishes target in water occlusion tracking technology. In order to realize multi-target tracking and positioning, we first design a novel fish target information acquisition platform. Then, according to optical imaging, geometry, digital image and video processing etc., we systematically discuss the basic technology of occlusion tracking, investigate the matching model of the real fish occlusion, imaginary fish occlusion, and both of them concurrently, and finally realize the 3D fish target non-occlusion tracking. We use four fishes, as an example, to design various type of occlusion experiments. The experimental results show the accuracy and effectiveness of the proposed fish 3D occlusion tracking model. Compared with the previous works, the information acquisition platform we designed is more simple and effective.

In vivo measurement of skin surface strain and sub-surface layer deformation induced by natural tissue stretching

Stratum corneum and epidermal layers change in terms of thickness and roughness with gender, age and anatomical site. Knowledge of the mechanical and tribological properties of skin associated with these structural changes are needed to aid in the design of exoskeletons, prostheses, orthotics, body mounted sensors used for kinematics measurements and in optimum use of wearable on-body devices. In this case study, optical coherence tomography (OCT) and digital image correlation (DIC) were combined to determine skin surface strain and sub-surface deformation behaviour of the volar forearm due to natural tissue stretching. The thickness of the epidermis together with geometry changes of the dermal-epidermal junction boundary were calculated during change in the arm angle, from flexion (90°) to full extension (180°). This posture change caused an increase in skin surface Lagrange strain, typically by 25% which induced considerable morphological changes in the upper skin layers evidenced by reduction of epidermal layer thickness (20%), flattening of the dermal-epidermal junction undulation (45–50% reduction of flatness being expressed as Ra and Rz roughness profile height change) and reduction of skin surface roughness Ra and Rz (40–50%). The newly developed method, DIC combined with OCT imaging, is a powerful, fast and non-invasive methodology to study structural skin changes in real time and the tissue response provoked by mechanical loading or stretching.

Riboflavin and chlorophyll as photosensitizers in electroformed giant unilamellar vesicles as food models

Electroformed giant unilamellar vesicles (GUVs) were found to have optimal sizes (~10 µm average diameter) for studying effects of photosensitizers and antioxidants in lipid bilayers as food models. By using optical microscopy and digital image processing techniques, no membrane damage was found for hydrophilic riboflavin, while lipophilic chlorophyll a initiated GUV budding and subsequent disintegration under light irradiation, indicating that lipophilic photosensitizers are the more important in such structured lipids. Lipophilic β-carotene provided protection against oxidative damage induced by chlorophyll a as shown by an increased lag phase for budding; however, it had no effect on subsequent budding rate. Hydrophilic puerarin alone exhibited little protection in terms of lag phase, but decreased together with β-carotene budding rate after the lag phase by a factor of more than 2, showing a clear synergistic effect between a hydrophilic antioxidant, inactive in the aqueous phase alone, and a lipophilic antioxidant protecting lipids.

Measurement of the condensation rate of vapor bubbles rising upward in subcooled water by using two ultrasonic frequencies

The condensation rate of vapor bubbles, defined by vc=−dR/dt where R is the spherical-equivalent bubble radius, t is time, is an important parameter to determine the interfacial-condensation heat and mass transfer in subcooled boiling. Previous measurements of the condensation rate were mainly based on the optical visualization. In the paper, the development of a new method that uses two ultrasonic frequencies for the measurement of the condensation rate in subcooled boiling is presented. The ultrasonic velocity profile (UVP) method is used for the velocity measurement. Two simultaneous UVP measurements by the two frequencies are exploited. The principle of the new condensation-rate-measurement method is established. In the method, the UVP data of the bubble surface velocity are used. In subcooled boiling, the bubble-surface velocity is affected by the condensation. The UVP measurement must capture correctly the condensation effect on the bubble-surface velocity. In order to confirm the applicability of the UVP method to the measurement of the surface velocity in this case, the growth rate of air bubbles from a nozzle submerged in water is measured and compared with the result of optical visualization and digital image processing. Such growth process is analogous to that of vapor bubbles in a boiling process, and it is the inverse of the condensation process. Evaluation of the new condensation-rate-measurement method is carried out by the measurements of adiabatic air–water-bubbly column and subcooled pool boiling in vertical round tube.

Measurements of strain fields around crack tips under proportional and non-proportional mixed-mode fatigue loading

For various configurations examined in a series of fatigue experiments on thin-walled tubes under tension and torsion, the experimental results – crack path, crack growth life, near crack tip deformations, and crack closure – are measured. Optical inspections and digital image correlation technique were used in the experimental investigation. Crack opening and closure loads were determined. The mechanical material behavior has been assumed as linear elastic in a first approach for calculating stress intensity factors. The non-linear nature of the cyclic deformation has been determined experimentally for future use in a cyclic plasticity model.

Convolutional Neural Networks기반 항공영상 영역분할 및 분류

Aerial scene is greatly increased by the introduction and supply of the image due to the growth of digital optical imaging technology and development of the UAV. It has been used as the extraction of ground properties, classification, change detection, image fusion and mapping based on the aerial image. In particular, in the image analysis and utilization of deep learning algorithm it has shown a new paradigm to overcome the limitation of the field of pattern recognition. This paper presents the possibility to apply a more wide range and various fields through the segmentation and classification of aerial scene based on the Deep learning(ConvNet). We build 4-classes image database consists of Road, Building, Yard, Forest total 3000. Each of the classes has a certain pattern, the results with feature vector map come out differently. Our system consists of feature extraction, classification and training. Feature extraction is built up of two layers based on ConvNet. And then, it is classified by using the Multilayer perceptron and Logistic regression, the algorithm as a classification process.

Astaxanthin Protecting Membrane Integrity against Photosensitized Oxidation through Synergism with Other Carotenoids.

Incorporation of astaxanthin or zeaxanthin in giant unilamellar vesicles (GUVs) of phosphatidylcholine resulted in a longer lag phase than incorporation of β-carotene or lycopene for the onset of budding induced by chlorophyll a photosensitization and quantified by a dimensionless entropy parameter using optical microscopy and digital image heterogeneity analysis. The lowest initial rate of GUV budding after the lag phase was seen for GUVs with astaxanthin as the least reducing carotenoid, while the lowest final level of entropy appeared for those with lycopene or β-carotene as a more reducing carotenoid. The combination of astaxanthin and lycopene gave optimal protection against budding with respect to both a longer lag phase and lower final level of entropy by combining good electron acceptance and good electron donation. Quenching of singlet oxygen by carotenoids close to chlorophyll a in the membrane interior in parallel with scavenging of superoxide radicals by astaxanthin anchored in the surface may explain the synergism between carotenoids involving both type I and type II photosensitization by chlorophyll a.

Application of supercomputer technologies for solving allocation of space objects in a digital image

The necessity of using supercomputers in the implementation of labor-intensive computational algorithms in the data processing systems of aerospace defence. For example, the algorithm selection in the optical digital image of cosmic objects show the feasibility of supercomputer technologies.

Transparent Aquabeads to Model LNAPL Ganglia Migration Through Surfactant Flushing

Light nonaqueous phase liquids (LNAPLs) represent potential long-term sources for continuing groundwater contamination. Their movement in the subsurface is controlled by several complex multiphase conditions because of soil heterogeneity and fluid saturations. The first part of this paper reviews previous experimental studies on LNAPL transport. For developing numerical models and remediation technologies, these studies reproduce the transport parameters, such as density, viscosity, capillary pressure, saturation and residual saturation, and relative permeability found in the subsurface environment. The second part presents 2D tank experiments of LNAPL ganglia migration using transparent synthetic soils. The main contribution of this part is to demonstrate the possibility for the transparent Aquabeads model for better simulation of macroscopic flow properties of natural soils. Transparent synthetic soil can visualize flow problems in the subsurface environment by an optical system and digital image processing. A water-based transparent material called Aquabeads is suitable for modeling flow properties of natural soils. Advantages of Aquabeads over available transparent synthetic soils include such features as their being a water-based material, having similar macroscopic hydraulic characteristics to natural soils, and compatibility with water- and oil-selected surfactants/alcohols used for simulating multiphase flow. Therefore, this transparent material is suitable for visualizing 2D flow and soil-contamination problems. Surfactant-flushing tests were conducted to model LNAPL ganglia transport through a multilayer Aquabeads model. This model visualized the concentration profile and upward migration of motor oil ganglia during surfactant flushing. The results showed the feasibility of surfactant flushing on multilayer soils using the Aquabeads model.

Interrupted Measurement Repositioning Using Elastic Averaging

In many cases, it is impractical or prohibitively expensive to develop new instrumentation to study tribological phenomena in situ, but with the application of elastic averaging, to accurately locate two surfaces with respect to one another, this can be realized with existing peripheral diagnostic equipment. A sample fixture was designed using the principles of elastic averaging that allows for the separation and repeatable repositioning of a tribological test specimen. Using an optical interferometer and digital image correlation, the fixture was determined to have average repositioning errors of <2 µm, in both the x and y directions. The application of these simple design principles could provide an accurate, repeatable, and low-cost solution for interrupted tribological studies.

A 3.7 M-Pixel 1300-fps CMOS Image Sensor With 5.0 G-Pixel/s High-Speed Readout Circuit

A 5.0 G-pixel/s readout circuit for 15.3 mm $\times$ 8.6 mm optical size, 3.7 M-pixel, 1300 fps, and digital output image sensor for industrial applications is presented. With the column parallel ADC, the speed bottleneck is the vertical analog readout. To achieve a 5.0 G-pixel/s readout rate, a high speed column readout circuit is introduced. The novel pixel readout with the slew-enhancement and the time-interleaved correlated double sampling circuit is introduced to increase the readout rate. Besides, the A/D converter with the delay-and-gray code counter and the distributed digital data transfer schemes are innovated in order to reduce the noise interference to the foreground analog signal settling. The 1 horizontal (1H) readout time is 1.0 $\mu$ s.

The quantification of digital activity fluorescence optical imaging of hand and wrist inflammation in rheumatic diseases

The quantification of digital activity fluorescence optical imaging of hand and wrist inflammation in rheumatic diseases

Tomographic diffractive microscopy with agile illuminations for imaging targets in a noisy background.

Tomographic diffractive microscopy is a marker-free optical digital imaging technique in which three-dimensional samples are reconstructed from a set of holograms recorded under different angles of incidence. We show experimentally that, by processing the holograms with singular value decomposition, it is possible to image objects in a noisy background that are invisible with classical wide-field microscopy and conventional tomographic reconstruction procedure. The targets can be further characterized with a selective quantitative inversion.

Three-dimensional information encryption and anticounterfeiting using digital holography.

In this work, arbitrary micro phase-step digital holography with optical interferometry and digital image processing is utilized to obtain information about an image of a three-dimensional object and encrypting keys. Then, a computer-generated hologram is used for the purpose of holographic encryption. All information about the keys is required to perform the decryption, comprising the amplitude and phase distribution of the encrypting key, the distance of image reconstruction, zero-order term elimination, and twin-image term suppression. In addition to using identifiable information on different image planes and linear superposition processing hidden within the encrypted information, not only can we convey an important message, but we can also achieve anticounterfeiting. This approach retains the strictness of traditional holographic encryption and the convenience of digital holographic processing without image distortion. Therefore, this method provides better solutions to earlier methods for the security of the transmission of holographic information.

Experimental Investigation on Dispersion of Water Droplets in the Single-Serpentine Channel of a PEM Fuel Cell

The polymer electrolyte membrane fuel cell (PEMFC) produces electrical power as a source of green energy with heat and water as the only byproducts. Proper water management in these fuel cells depends on the study and characterization of water droplets. In the present study, the dispersion of water droplets in the cathode channel of a transparent PEMFC with single-serpentine flow field is studied by optical visualization and digital image processing for different inlet flow parameters and operational conditions. The dispersion and detachment of liquid water droplets are quantified and a schematic map of water droplet dispersion is presented.