Two-dimensional Digital Image Research Articles

Low-cost two-dimensional digital image correlation system

A low-cost digital image correlation (DIC) system for measuring two-dimensional displacement fields is described. Using an off-the-shelf camera, lens, and open-source DIC analysis software, displacement fields in aluminum and steel dog-bone tensile specimens were measured. Correction for out-of-plane motion is used to obtain strains from the displacement fields. Proposed DIC strain measurement system is validated using conventional thin-film strain gauges for strains below 1%. Average strain measurements from the DIC system were found to be within 1% of the measurement obtained using strain gauges. For strains between 1% and 10%, strain histories from the DIC systems displayed excellent correlation with strain measurements obtained using an extensometer.

Strain Rate Sensitivity of Rotating-Square Auxetic Metamaterials

This study provides an in-depth analysis of the mechanical behavior of rotating-square auxetic structures under various strain rates. The structures are fabricated using stereolithography additive manufacturing with a flexible resin. Mechanical tests performed on structures include quasi-static, intermediate, and high strain rate compression tests, supplemented by high-speed optical imaging and two-dimensional digital image correlation analyses. In quasi-static conditions (5 × 10-3 s-1), multiscale measurements reveal the correlation between local and global strains. It is shown that cell hinges play a significant role in structural deformation and load-bearing capacity. In drop tower impact conditions (intermediate strain rate of ca. 200 s-1), the auxetic structures display significant strain rate hardening compared to loading at quasi-static rates. The thin-hinge structures maintain a Poisson's ratio of approximately -0.8, showing higher auxeticity than slow-rate compression tests. High strain rate conditions (ca. 2000 s-1) activate additional deformation mechanisms, including a delayed state of equilibrium exemplified by a heterogeneous distribution of lateral strains, possibly due to stress wave interactions and inertial stresses. The study further reveals nonlinear correlations between Poisson's ratio, strain, and strain rate, indicating reduced auxeticity at higher strain rates. These observations are discussed in terms of complex wave interactions and the strain rate hardening characteristics of the base polymer.

Adaptive matching strategies for 3D digital image correlation in strain measurement of an aerostat envelope

To address the limitations of two-dimensional digital image correlation (2D-DIC) in measuring strain on the aerostat envelope, the more precise 3D-DIC has been introduced to handle curved surfaces. However, the increased computational load of 3D-DIC requires more efficient correlation strategies. This paper evaluates three basic matching strategies and introduces two adaptive strategies to enhance the efficiency of 3D-DIC. The experimental results show that the adaptive composite matching (ACM) strategy automatically switches strategies based on deformation, improving the matching correlation. Meanwhile, the adaptive grouping matching (AGM) strategy dynamically adjusts image groups based on real-time data, optimizing the computational speed and enhancing measurement flexibility. These strategies provide crucial support for the application of 3D-DIC in the monitoring aerostat envelope strain, especially in managing significant or uneven deformations.

Effect of gravity number on soil contamination during dynamic adsorption of heavy metal ions: A lattice Boltzmann study

Contamination of soils and aquifers as a result of heavy metal ions adsorption is an extremely negative environmental phenomenon associated with natural or industrial disasters. This paper presents the first systematic study of the dynamic adsorption of heavy metal ions in soils during water-air immiscible displacement induced by pressure drop and gravitational force. This study addresses three objectives. The first purpose is to determine a representative elementary volume to estimate the adsorbed amount of heavy metal ions during two-phase flow with density contrast. The second objective is to study the effect of different balances between viscous and gravitational forces, described by the gravity number, on the adsorbed amount at drainage and imbibition regimes. And the final task is to identify the effect of the pore space heterogeneity on the adsorbed amount for various gravity numbers and wetting conditions. As samples of study, we examine two-dimensional granular digital images characteristic of soils. The lattice Boltzmann method, verified on the problem of capillary-gravitational equilibrium of a meniscus, was used as a research tool. It has been established that the scale of 4–5 mm is sufficient to be representative for estimating the adsorbed amount of heavy metal ions. An increase in gravity number promotes the destabilization of the interfacial front both in the drainage and imbibition regimes and results in suppression of the adsorbed amount. The effect of gravity number on the adsorbed amount is stronger in the drainage mode compared to the imbibition regime. It has been found that pore space heterogeneity is a factor negatively affecting the adsorbed amount of heavy metal ions. The strength of the heterogeneity effect is independent of wetting conditions and gravity numbers.

Three-dimensional ranging system based on Fresnel incoherent correlation holography.

We proposed a three-dimensional (3D) ranging system based on Fresnel incoherent correlation holography (FINCH). Distinct from the displacement measurement based on coherent digital holography (DH), our system simultaneously achieves a 3D range measurement using incoherent illumination. The observation range is obtained by the holographic reconstruction, while the in-plane range is determined using the two-dimensional digital imaging correlation (2D-DIC) technique. Experimental results on the resolution target demonstrate precise 3D ranging determination and improved measurement accuracy.

Revealing crack initiation and extension of brittle rock via time-lapse acoustic attenuation: Insights from active ultrasonic experiments

Predicting brittle rock failure is essential for rock mechanics research and early disaster alerts in deep rock engineering. Successful prediction relies on identifying crack initiation and extension. However, currently, there is no universally accepted method for accurately identifying and tracking crack evolution to predict brittle failure of the surrounding rock. In this study, the propagation parameters of transmission ultrasonic waves were used to characterize crack behaviors at the laboratory scale. The differential acoustic attenuation term was proposed by modifying the spectral ratio method to evaluate the dissipation capability of the corresponding medium to the transmitted ultrasonic waves. In addition to acoustic attenuation, velocity and amplitude attenuation were introduced to characterize the damage evolution during brittle failure. The indicators were analyzed by conducting a uniaxial compression test on a sandstone sample with a single flaw. During compression, active ultrasonic surveys were conducted to attain the propagation parameters. The two-dimensional digital image correlation method was simultaneously applied to capture the full-field strain on the front surface of the sample. The shear and tensile strain profiles indicated that the shear damage initially accumulated at the tips of the flaw, causing a reduction in the velocity and amplitude of the transmitted ultrasonic waves. The acoustic attenuation indicator in the flaw-tip regions increased before the shear strain began. As the damage developed further, the acoustic attenuation increased overall, with numerous local fluctuations in the flaw-tip regions due to stress rearrangement and damage development, while the velocity and amplitude remained consistently low. In contrast, intact regions that were far away from the tips of the flaw exhibited different characteristics. The velocity and amplitude variations were more staged, while the acoustic attenuation changed gradually. The results indicated that the variations in the propagation parameters exhibited specific patterns before the damage was initiated, offering a potential for predicting crack initiation. The variations in the acoustic attenuation, velocity, and amplitude attenuation allow for tracking the crack propagation.

Eligibility of a novel BW + technology and comparison of sensitivity and specificity of different imaging methods for radiological caries detection

ObjectivesBitewing radiography is considered to be of high diagnostic value in caries detection, but owing to projections, lesions may remain undetected. The novel bitewing plus (BW +) technology enables scrolling through radiographs in different directions and angles. The present study aimed at comparing BW + with other 2D and 3D imaging methods in terms of sensitivity, specificity, and user reliability.Materials and methodsFive human cadavers were used in this study. In three cadavers, natural teeth were transplanted post-mortem. BW + , two-dimensional (digital sensors, imaging plates, 2D and 3D bitewing radiographs) and 3D methods (high and low dose CBCT) were taken. Carious lesions were evaluated on 96 teeth at three positions (mesial, distal, and occlusal) and scored according to their level of demineralization by ten observers, resulting in 35,799 possible lesions across all observers and settings. For reference, µCT scans of all teeth were performed.ResultsOverall, radiographic evaluations showed a high rate of false-negative diagnoses, with around 70% of lesions remaining undetected, especially enamel lesions. BW + showed the highest sensitivity for dentinal caries and had comparatively high specificity overall.ConclusionsWithin the limits of the study, BW + showed great potential for added diagnostic value, especially for dentinal caries. However, the tradeoff of diagnostic benefit and radiation exposure must be considered according to each patient’s age and risk.

Computer Vision-Based Estimation of The Effects of Vibration in Slipform Paving

Slipform paving is a complex multistep process encompassing concrete pouring, vibration, consolidation, correction, and curing. One of the most critical aspects in the process is that the frequency and duration of vibration can influence the distribution of coarse aggregate particles in the cured concrete. However, there is still a fundamental lack of methodologies to formally characterize the interrelationships between vibration characteristics and the quality of the cured pavement. This study aims to address this issue by proposing a novel toolset for the assessment of the spatial features of coarse aggregate distribution in doweled pavements. This system is based on paver consolidation simulations and employs computer vision as the primary tool for analysis. The experimental protocol, recently developed by the authors, employs coarse aggregate particles color-coded by gradation to aid in recognizing the distribution of different granulometric sizes within the specimens. High-resolution, two-dimensional digital images obtained from cured specimens were used to analyze aggregate characteristics, orientation, and dispersion, with particular emphasis on quantifying the effect of the distance from the vibrator head on such parameters. The results showed that the proposed digital imaging processing techniques were capable of quantitatively characterizing the distribution of coarse aggregate particles in the specimens. Moreover, novel metrics were proposed to characterize the quality of the consolidation based on the digital image data.

A novel experimental technique to determine the tack development during automated placement of uncured thermoset carbon/epoxy tows

In-situ bond strength toughness (IBST), commonly referred to as tow tackiness, is a first order property affecting the adherence quality and defect formation (e.g., wrinkles, folds) during automated tow placement (ATP) processing of uncured thermoset polymer matrix composite (PMC) tows. Tow-tow IBST develops over characteristic millisecond timescales (tc≤50ms) due to the rapid tow placement velocity of ∼1 m/s. In this paper, an experimental technique is presented to determine millisecond timescale tow-tow mode-I IBST in terms of fracture mechanics-based traction-separation relationship. The test specimen consists of two tows bonded to rigid platens with a pre-crack between them to induce crack initiation. Experiments are performed using IM7-G/8552 carbon/epoxy prepregs for both long and short timescales at a constant debonding rate of 5 mm/s, contact pressure of 0.23 MPa, and bonding temperature of 40 °C. In addition, high-speed two-dimensional digital image correlation (2D-DIC) is used to image and measure the tow-tow interfacial deformation during debonding. The peak traction and apparent energy release rate are found to significantly decrease (about 60 %) at the short millisecond timescale contact hold times compared to longer (i.e., second) timescale.

Experimental Study of Strain Measurement using 2D Digital Image Correlation on Fixation Plate and Calcaneus Bone Fracture

The plate and screw internal fixation technique is widely used for the treatment of fractured bones. Determining the mechanical behavior of bone plates under load conditions remains challenging, as it is anisotropic, non-linear, and inhomogeneous. Bone strain is frequently measured using strain gages, but they can only measure the strain at a single point. The optical method known as digital image correlation (DIC) provides the displacement and consequently the strain over the entire region of interest on the bone surface. The objective of this study was to investigate the strain changes in the surface of a calcaneus plate fixation during load compression using the digital image correlation method. In this study, a two-dimensional digital image correlation (2D-DIC) and strain gauges-based experimental methodology for calculating calcaneal plate strains is presented. A 500 N static load was applied to a synthetic calcaneus that was both plate-covered and intact. A Sanders type II fractured calcaneus was stabilized with stainless steel (316L) plate. At the same locations on the calcaneus plate, displacement and strains were recorded. According to the results of the DIC method, the maximum strain values along the x, y, and shear directions were 0.008, 0.010, and 0.012 mm, respectively, while the measurement result for the strain gauge was 0.0015 mm. The experimental result had a slightly lower strain gauge than the DIC method’s output. The results of the experiment and the DIC were thought to be in good agreement.

Body weight prediction in crossbred pigs from digital images using computer vision

The development of technologies made it possible to capture digital images by sensors in order to obtain morphometric measurements that can be used in the development of mathematical models for the prediction of body weight (BW) in animals. The objective was to develop mathematical models to predict body weight in crossbred pigs from morphometric measurements obtained with two-dimensional digital images. Data collection was carried out in the swine sector of IF Goiano, Urutai campus, in 52 crossbred pigs housed in the finishing phase. The animals were randomly weighed and filmed by the Microsoft Kinect® v1 sensor camera in the dorsal view. Subsequently, they were conducted for the measurement of manual morphometric measurements, without restraint, being dorsal length, chest width and flank width. The morphometric measurements predicted from the dorsal images were dorsal length, chest width, flank width, dorsal area and perimeter. Through Mask R-CNN algorithm trains the network by input images, was compute the area of the evaluated object in pixels, and thus, can correlate with measures of interest. The Mask R-CNN algorithm were performed with the Collaboratory Google using Phyton 3.0. Mathematical models were developed using multiple linear regression (MLR) and support vector regression (SVR) methodologies for body weight prediction. All Pearson's correlations between real body weight and real and predicted morphometric measurements by digital images were moderate to high magnitude positive and statistically significant (P<0.05). The difference between the real and predicted BW by the SVR was -1.74 kg (R² = 91%) and -2.39 kg (R² = 88%), respectively. The MLR model with real morphometrics measurements explained 60% of BW variance and estimated a BW 18.76 kg below from the real BW mean. The MLR model with predicted measurements explained 53% of BW variance and estimated a BW 22.51 kg below from the real BW mean. The mathematical model developed from SVR has the potential to estimate the body weight of crossbred pigs using morphometric measurements predicted by digital images such as dorsal length, width, dorsal area and perimeter.

Multi-thread two-dimensional digital image correlation for full-field displacement and rotation angle measurement

Multi-thread two-dimensional digital image correlation for full-field displacement and rotation angle measurement

Global and Local Deformation Analysis of Mg-SiC Nanocomposites: Digital Image Correlation (DIC) and Representative Volume Element (RVE) Techniques

Improving the ductile deformation behavior of Mg-SiC nanocomposites without compromising strength is critical to enhancing their mechanical properties. Mg-SiC nanocomposites are produced through mechanical milling, cold isostatic pressing, sintering, and hot extrusion processes. This study investigates the uniaxial stress–strain response and deformation behavior of the Mg-SiC nanocomposite compared to pure Mg samples with and without the milling process. The deformation behavior was investigated by two-dimensional (2D) digital image correlation (DIC) at two macroscopic and microscopic scales, employing light micrographs and in situ loading samples, respectively, in the scanning electron microscope. Compared to the pure Mg samples, the mechanical test results demonstrated a significant improvement in strength (80 MPa) and fracture strain (23.5%) of the Mg-SiC nanocomposite. The three-dimensional (3D) representative volume element (RVE) model revealed the particle dispersion effect on the mechanical properties of the nanocomposite. The RVE results demonstrate ductile deformation behavior in the sample with homogenous dispersion of SiC particles compared with the heterogeneous dispersion of SiC particles in Mg-SiC nanocomposite. The results demonstrated a good agreement between DIC and RVE predictions for Mg-SiC nanocomposites across macro- and microscales.

Performance of delaminated CFRP composite under pure bending using two-dimensional digital image correlation

ABSTRACT Delamination is an interlaminar damage which may be pre-existing in multilayered fibre reinforced polymer composite parts due to manufacturing imperfections or generated by out of plane loading during service life. Its existence leads to significant reduction of structural integrity, strength and stiffness of the material. Hence, to study the effect of induced delamination on the performance of a composite under pure bending, a circular polytetrafluoroethylene (PTFE) film was introduced between the second and third plies of a sixteen layered carbon/epoxy laminate during fabrication. The bending tests were conducted in displacement control mode. The displacements and strains were measured through the thickness of the composite using two-dimensional digital image correlation. The damage modes were captured using CCD camera and the causes were explained. The flexural strength and modulus of composite were 329.74 MPa and 104.58 GPa respectively. The delaminated composite behaved as a single member without any crack within the elastic range. The existence of PTFE drastically reduced flexural stiffness of composite beyond the stress at 75.81% of its ultimate strength. The ± 45º plies offered low mechanical performance against the induced off axis loading. Hence, in these plies fibre breakage was higher. In the portion of PTFE, the strains were higher due to larger outward displacements produced by local buckling.

Optimization of aggregates skeleton using laser-scanning technology and discrete element method

The skeletonof aggregates hasasignificanteffecton the performance of porous asphalt mixtures. In this study, laser-scanning technology was utilized to obtain two-dimensional digital images of four groups of aggregates with different particlesizes. Digitalimage processing technology was used to obtain the basic dimensional indicessuch asarea, perimeter, and equivalent ellipse of aggregate particles. Based ontheseindices, the morphological characteristics of theaggregates,including aspect, roundness, andangularity,were evaluated.Then,virtual uniaxial penetration tests were simulated via the discrete element method (DEM) and verified by the results of laboratory uniaxial penetration tests. On this basis, the visualization design of the optimal main skeleton for the porous asphalt mixture was conducted. Results show that the shapes of the aggregateswereclose to cubes. Aggregates with sizes greater than 4.75 mmhada more significant structural effect on the skeleton than those with sizes smaller than 2.36 mm. Coarse aggregatescouldform a stable skeleton by interlocking with each other, whereas the skeleton formed by fine aggregateswasfragile. Coarse aggregates primarilywithstoodthe external load while fine aggregates primarilylimitedthe displacement of coarse aggregates. The optimal main skeleton designed by combining the DEM with the laser-scanning technology can provide new possibilities for the gradation design of porous asphaltmixtures.

Crack Detection of Asphalt Concrete Using Combined Fracture Mechanics and Digital Image Correlation

Cracking is a common failure mode in asphalt concrete (AC) pavements. Many tests have been developed to characterize the fracture behavior of AC. Accurate crack detection during testing is crucial to describe AC fracture behavior. This paper proposes a framework to detect surface cracks in AC specimens using two-dimensional digital image correlation (DIC). Two significant drawbacks in previous research in this field were addressed. First, a multiseed incremental reliability-guided DIC was proposed to solve the decorrelation issue due to large deformation and discontinuities. The method was validated using synthetic deformed images. A correctly implemented analysis could accurately measure strains up to 450%, even with significant discontinuities (cracks) present in the deformed image. Second, a robust method was developed to detect cracks based on displacement fields. The proposed method uses critical crack tip opening displacement (δc) to define the onset of cleavage fracture. The proposed method relies on well-developed fracture mechanics theory. The proposed threshold δc has a physical meaning and can be easily determined from DIC measurement. The method was validated using an extended finite-element model. The framework was implemented to measure the crack-propagation rate while conducting the Illinois-flexibility index test on two AC mixes. The calculated rates could distinguish mixes based on their cracking potential. The proposed framework could be applied to characterize AC cracking phenomenon, evaluate its fracture properties, assess asphalt mixture testing protocols, and develop theoretical models.

Tensile performance of aluminum alloy roof panel-member clamp connection

In aluminum alloy reticulated shell structures with gusset joints, the roof panel is effectively connected with the structural members through a clamp connection, enabling the roof panels to participate in the force resisting system. The performance of the connection between the roof panels and the members is the foundation for studying the collaborative action of the roof panels and the members. Relevant studies have shown that when the roof panels participate in the force resisting system, there is mainly a tensile force in the roof panels perpendicular to the axis of the members. Therefore, this paper experimentally studied the mechanical performance of the clamp connection between the roof panels and the members under the tensile force in the roof panels, and employed two-dimensional plane digital image correlation (DIC) to measure the deformation of the specimen section during the entire loading process, thus exploring the force transmission mechanism of the connection. The tensile capacity of the connection can be divided into four stages: roof panel sliding, roof panel tension–shear, lower limb bending of the strip, and roof panel bending stages. The mechanical index of the connection is primarily determined by the tension–shear stage of the roof panel, and the ultimate strength and stiffness can be determined as the peak load and linear segment stiffness of the connection at this stage. The refined finite element model was further established, and it was verified that the model could efficiently simulate the mechanical properties of the connection through comparison with the test. Parametric analysis shows that with an increase in the friction coefficient between materials, roof panel thickness, angle between roof panel and flange, and bolt length adjustment, the restraint on the roof panel increases, and the failure mode of the clamp connection changes. Based on the parametric analysis, the recommended values of the friction coefficient between the materials, minimum panel thickness, minimum bolt screw depth, and maximum bolt spacing are provided. Finally, combined with the theoretical analysis, calculation formulas for the tensile strength and stiffness of the connection were proposed. A comparison with the test results indicates that the prediction accuracy of the formula proposed in this study is good.

Construction of artificial intelligence non-invasive diagnosis model for common glomerular diseases based on hyperspectral and urine analysis

ObjectiveTo develop a non-invasive fluid biopsy assisted diagnosis model for glomerular diseases based on hyperspectral, so as to solve the problem of poor compliance of patients with invasive examination and improve the early diagnosis rate of glomerular diseases. MethodsA total of 65 urine samples from patients who underwent renal biopsy from November 2020 to January 2022 in Qianfoshan Hospital of Shandong Province were collected.By simultaneously capturing spectral information of the above urine samples in the 400–1000 nm range, more obvious differences were found in the spectra of urine from patients with glomerular diseases between 650 nm and 680 nm. We obtained the original hyperspectral images in this wavelength range through digital scanning, and sampled pixel points at intervals on the original images. The two-dimensional digital image generated from each pixel point served as a member of the subsequent training and test sets. . After manually labeling the images according to different biopsy pathological types, they were randomly divided into training set (n = 58,800) and test set (n = 25,200). The training set was used for training learning and parameter iteration of artificial intelligence non-invasive liquid diagnosis model, and the test set for model recognition and interpretation. The evaluation indexes such as accuracy, sensitivity and specificity were calculated to evaluate the performance of the diagnosis model. ResultsThe model has an accuracy rate of 96% for early diagnosis of four glomerular diseases. ConclusionThe auxiliary diagnosis model system has high accuracy. It is expected to be used as a non-invasive diagnostic method for glomerular diseases in clinic.

Influence of Recycled Cement Paste Powder on Early-Age Plastic Shrinkage and Cracking of Cement-Based Materials

Cement-based materials, especially those with low water-cement ratios, often experience premature cracking due to plastic shrinkage in the early curing stages. In this study, the development mechanism of early-age plastic shrinkage of cement paste, and the crack shrinkage control effect of recycled cement paste powder on cement paste, was quantitatively investigated using non-contacting two-dimensional digital image technology. The influence of different replacement rates (5%, 10%, 20% and 30%) of recycled cement paste powder on the major principal strain and crack patterns of cement paste was investigated. Furthermore, the mechanism of recycled cement paste powder on the early-age plastic shrinkage of cement-based materials was explored. The results show that the addition of recycled cement paste powder could suppress the early-age plastic shrinkage of cement paste. An appropriate replacement ratio (10%) of recycled cement paste powder shows a 33.3% time delay in crack appearance and a 28.0% reduction in the major principal strain. However, the higher replacement ratio of 30% shows an adverse effect on the major principal strain, with an increase of 35.1%. The core mechanism of the appropriate recycled cement paste powder on plastic shrinkage reduction lies in its porous nature, which allows for water absorption and release and regulates the moisture state inside the pores. This quantitative research of the major principal strain development of the early-age plastic shrinkage of cement paste can facilitate a better understanding of plastic shrinkage reduction in recycled cement paste powder on cement paste.

Projectile Impact on Plain and Reinforced Concrete Slabs

Reinforced concrete is a material frequently used in protective structures and infrastructure exposed to extreme loading. In this study, the ballistic perforation resistance of 100 mm thick plain and reinforced concrete slabs impacted by 20 mm ogive-nose steel projectiles was investigated both experimentally and numerically. Two different reinforcement configurations were used to investigate the effect of rebar diameter and spacing. Concrete with nominal unconfined compressive strength of 75 MPa was used to cast material test specimens and slabs. Ballistic impact tests were performed in a compressed gas gun facility. The mechanical properties of the concrete were found using standardised tests and two-dimensional digital image correlation, and the constitutive relation was described by a modified version of the Holmquist-Johnson-Cook model. Finite element models in LS-DYNA reproduced the projectile residual velocity in good agreement with the experimental results. The primary objective of the study was thus to validate a rather simple constitutive relation intended for large scale numerical simulations of concrete structures exposed to ballistic impact loading, while a secondary objective was to investigate the effect of reinforcement on the ballistic perforation resistance of concrete slabs both experimentally and numerically since the literature is somewhat inconsistent on this matter.