3D Digital Image Correlation Method Research Articles

A speckle projection-based 3D digital image correlation method for measuring dynamic liquid surfaces

A speckle projection-based 3D digital image correlation method for measuring dynamic liquid surfaces

Thickness evaluation of organic coating using active long-pulse transmission thermography

The thickness of the optically translucent coating was evaluated using the transmission thermography. The transmitted temperature of a two-layer structure was theoretically analysed based on the equation of 1D heat transfer in the depth direction, and accordingly, the method for the measurement of coating thickness in a two-layer structure was established based on a long-pulse transmission thermography. The coating thickness was determined based on the characteristic time at the maximum half-rise temperature. Then, the proposed method was experimentally validated and calibrated by coating specimen with a different coating thickness. The thickness measurement method was further applied to measure an uneven coating specimen fabricated by mechanical grinding. The measurements were compared with a 3D digital image correlation method and the averaged relative error was less than 4%. Finally, thermal excitation, sampling rate of thermography and translucence of organic coating were discussed for accurate measurement.

Multiple-view 3D digital image correlation based on pseudo-overlapped imaging.

The restriction of the field of view (FOV) enlargement and spatial resolution increase during optical monitoring was investigated. Traditional optical instruments usually have a fixed FOV in one test; thus, they have low accuracy for small samples under large motions/deformations. To improve the spatial resolution in a relatively large FOV of an optical instrument, a multiple-view 3D digital image correlation (3D-DIC) method based on pseudo-overlapped imaging is proposed. Using a set of optical components, pseudo-overlapped imaging can image two FOVs with the same camera, which converts one pair of cameras to four virtual cameras. Each virtual camera has the same whole pixels. Therefore, compared with the conventional 3D-DIC system, the proposed method simultaneously enlarges FOVs and increases spatial resolutions by two times. The efficiency, accuracy, and feasibility of the technique were validated through experiments.

Digital image correlation techniques for motion analysis and biomechanical characterization of plants.

Temporally and spatially complex 3D deformation processes appear in plants in a variety of ways and are difficult to quantify in detail by classical cinematographic methods. Furthermore, many biomechanical test methods, e.g. regarding compression or tension, result in quasi-2D deformations of the tested structure, which are very time-consuming to analyze manually regarding strain fields. In materials testing, the contact-free optical 2D- or 3D-digital image correlation method (2D/3D-DIC) is common practice for similar tasks, but is still rather seldom used in the fundamental biological sciences. The present review aims to highlight the possibilities of 2D/3D-DIC for the plant sciences. The equipment, software, and preparative prerequisites are introduced in detail and advantages and disadvantages are discussed. In addition to the analysis of wood and trees, where DIC has been used since the 1990s, this is demonstrated by numerous recent approaches in the contexts of parasite-host attachment, cactus joint biomechanics, fruit peel impact resistance, and slow as well as fast movement phenomena in cones and traps of carnivorous plants. Despite some technical and preparative efforts, DIC is a very powerful tool for full-field 2D/3D displacement and strain analyses of plant structures, which is suitable for numerous in-depth research questions in the fields of plant biomechanics and morphogenesis.

Stress-strain analysis of steel S235JRH pipe ring tensile specimens using 3D optical methods

Various pipe production procedures, including the construction of seamless pipes using a shaft with the conical tip in the oil industry, require data on the circumferential strain and stress state of the pipe. A method for measuring the displacement, strain and stress behavior of a pipe ring tensile specimen (PRTS) in the hoop direction is what this study’s goal was to develop, as there was a lack of a standardized testing process. For the study, five single S235JRH steel PRTS were tested. In the paper, it is presented how to test S235JRH steel PRTS using a Digital Image Correlation method, Thermal Imaging camera, and 3D scanner. A specially designed steel tool with two D blocks was developed for testing steel PRTS. The strain progression was documented using the 3D Digital Image Correlation method. Using a thermographic camera, an attempt was made to analyze the change in the temperature field of the PRTS during the test. All the specimens were subjected to 3D scanning to verify the cross-sectional geometry of the PRTS after a fracture. Fractures of all Single PRTS occurred in the break zone and almost identical places. The deviation value for the Experimental Ultimate strength value (true stress value) higher than the theoretical Ultimate strength value. Deviation value for the Experimental 0.2% Offset Yield Strength value is higher than the theoretical value. The results of the analysis of cross-sectional dimensions revealed a more significant variation in the thickness of the PRTS compared to its width. A potential area of literature review is the application of a high-resolution thermal imaging camera and the analysis of the stress state of the material using it.

Investigation on the off-axis tensile failure behaviors of 3D woven composites through a coupled numerical-experimental approach

Computational models with high precision and efficiency are in urgent need for the damage analyses of 3D angle-interlock woven composites which are widely accepted in composites industry. A novel concurrent multi-scale damage evolution modeling scheme is established based on a meso-scale representative volume cell (RVC) model and the multiphase finite element method to characterize the off-axis tensile response of carbon/epoxy composites. Modified Puck criterion and maximum shear stress criterion are adopted for fiber yarns. Parabolic yield criterion is adopted for the matrix. The fiber breakage, the inter-fiber fracture and matrix cracking are considered at mesoscopic level. To validate the proposed multi-scale damage model, off-axis tensile test is conducted with the help of 3D Digital Image Correlation (DIC) method. A reasonably good agreement is achieved between numerical predictions and experimental observations. Furthermore, the validated damage model is used to predict the tensile response of the composites considering full range on-axis and off-axis angles.

3D Digital Image Correlation Analysis of Local Deformation Field of Different Endodontic Calcium Silicate Cements

The objective was to compare the strain of three calcium silicate cements using an optical system based on the 3D digital image correlation method (3D-DIC). Dentine disks from 30 upper premolars were sectioned transversely to obtain 2 mm-thick sections and enlarged with a 4 mm diameter bur. An additional 30 samples were made in Teflon molds (4 × 2 mm). Dentine discs and Teflon molds were divided into three groups with ten samples each and then filled with MTA+ (Cerkamed), Biodentine (Septodont) and Well-Root PT (Vericom). The strain was determined using the 3D-DIC method in two zones: the peripheral and central zones. Data were analyzed using ANOVA with Scheffe’s post hoc test, a paired t-test and Pearson correlation (α = 0.05). Analysis showed that there were significant differences in the values of deformation between all tested materials in both zones. Comparing the strain in both zones, there were significant differences between zones in the Biodentin and Well-Root PT group on dentine discs, and in the Biodentine and MTA group on Teflon discs. Comparing the strain measured on different disc types, the higher values were found on Teflon. All the examined calcium silicate-based cements showed deformation after initial setting. The highest strain was recorded for Biodentine and the lowest was for Well-Root PT.

Metrological Evaluation of the Demosaicking Effect on Colour Digital Image Correlation with Application in Monitoring of Paintings.

A modified 3D colour digital image correlation method (3D cDIC) is proposed for efficient displacement measurements of colour objects with natural texture. The method is using a separate analysis of correlation coefficient (sigma) value in the RGB channels of CCD cameras by utilising local information from the channel with the minimum sigma. In this way, merged U, V and W displacement maps are generated based on the local correlation quality. As the proposed method applies to colour filter array cameras, the images in RGB channels have to undergo a demosaicking procedure which directly influences the accuracy of displacement measurements. In the paper, the best performing demosaicking methods are selected. The metrological analysis of their influence on the results of canvas paintings investigations obtained by unmodified and modified 3D cDIC processing is presented.

Stereovision-based method for free vibration measurement of a mine hoisting rope

Currently, there are no suitable means to measure the composite vibration response of mine hoisting rope. However, machine vision-based measurement technology is a potential way to solve this problem. Therefore, a non-contact and non-intrusive stereovision method is proposed to obtain the 2D vibration displacement of a moving hoisting rope. In this methodology, a novel 3D digital image correlation (DIC) method that combines digital image processing (DIP) algorithm with 2D-DIC algorithm is developed, and the method can simplify the procedure of rope target stereo matching in two synchronous image sequences. In order to confirm the correctness of the stereovision method, some free vibration responses of a rope are measured in a hoist experimental system. Test results demonstrate that the stereovision measurement technique can keep satisfactory consistency with the laser displacement sensor for vibration data identification. The method is verified to have high adaptability to different lighting conditions and be reasonable to measure the vibration parameters of dynamic mine hoisting rope.

Effect of natural aging time on anisotropic plasticity and fracture limit of Al7075 alloy

Numerical approaches for fracture modeling have been proposed for various metallic materials, including high-strength steels and aluminum alloys. However, the quantitative relationship between the Portevin–Le Chatelier (PLC) effect and the fracture initiation has not been yet fully explored, considering the influence of the natural aging time (NA) on the material deformation behavior. To address this gap, this study investigated the PLC effect on the anisotropic plasticity and fracture limit of Al7075 alloy according to the natural aging time. Aging behavior and PLC effects are experimentally evaluated through uniaxial tensile and fracture tests using the 3D digital image correlation method. The natural aging-dependent PLC effect is tracked in the visualization of the strain rate map and thickness strain distributions with plastic deformation. Variations in the anisotropic plasticity are captured using Barlat’s YLD2000‐2d anisotropic yield function at different natural aging times, and fracture envelopes that cover general 3D stress states are identified based on the Lou–Huh ductile fracture criterion. A natural aging-dependent fracture modeling approach is proposed to predict the influence of natural aging on the fracture limit transition. Finally, the strain- and stress-based fracture forming limit diagrams, including their corresponding magnitude of the stress vector, are represented. The results reveal that no general trend for the natural aging-dependent fracture limit based on the strain metric is observed, whereas the fracture limit based on the stress metric tends to increase with natural aging in various loading conditions.

Determination of Mechanical Properties of Epoxy Composite Materials Reinforced with Silicate Nanofillers Using Digital Image Correlation (DIC).

In this study, silicate nanofillers; dicalcium silicate, magnesium silicate, tricalcium silicate, and wollastonite; were synthesized using four different methods and incorporated into the epoxy resin to improve its mechanical properties. Characterization of the newly synthesized nanofillers was performed using Fourier-transformation infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The purpose of this study was to analyze newly developed composite materials reinforced with silicate nanoparticles utilizing tensile testing and a full-field non-contact 3D Digital Image Correlation (DIC) method. Analysis of deformation and displacement fields gives precise material behavior during testing. Testing results allowed a more reliable assessment of the structural integrity of epoxy composite materials reinforced using different silicate nanofillers. It was concluded that the addition of 3% of dicalcium silicate, magnesium silicate, tricalcium silicate, and wollastonite lead to the increasement of tensile strength up to 31.5%, 29.0%, 27.5%, and 23.5% in comparison with neat epoxy, respectively. In order to offer more trustworthy information about the viscoelastic behavior of neat epoxy and composites, a dynamic mechanical analysis (DMA) was also performed and rheological measurements of uncured epoxy matrix and epoxy suspensions were obtained.

An experimental study of the dynamic responses of carbon fiber reinforced polymer composite laminates subjected to ice impact

The aircraft structures are threatened by soft material impact such as birds and hail ices. The main objective of this study is to develop a comprehensive experimental method to evaluate the resistance performance of carbon fiber reinforced polymer laminate subjected to ice impact loadings. First, a hollow tube sensor was adopted to measure the impact force of ice projectiles. Based on the deformation process captured by a high-speed camera and the analysis on transmitted energies obtained by the tube sensor, the repeatability of the ice impact loadings was confirmed and its impact behavior was analyzed. Second, six T700/epoxy carbon reinforced polymer laminates were impacted with different loading velocities, where the transient deformation data during impact were obtained by 3D digital image correlation method The post-test detection was realized using both optical microscopes and scanning acoustic microscopes. The impact of ice projectiles resulted in distributed loadings on the laminate targets with invisible inner matrix cracks and delaminations. Irregular distributions of delaminated areas subjected were observed and their sized increased with the impact velocity. The experimental method showed its practicability on impact issues with projectiles of unknown properties.

Spatio-temporal monitoring of humidity induced 3D displacements and strains in mounted and unmounted parchments

The high hygroscopicity and heterogeneity of parchment make it particularly sensitive to changes in environmental conditions. The proper housing of a historical parchment, including mounting should mitigate the impact of the changes on the object. However, finding an appropriate mounting method requires detailed knowledge of the mechanical response of a parchment on the combined influence from environmental changes and forces introduced by the mounting. In this paper we present the capabilities of 3D digital image correlation (3D DIC) method implemented for full-field, spatio-temporal monitoring of displacements and strains in parchment exposed to environmental changes. We combine the measurement concept with the particular, critical task of evaluating the effectiveness of stabilising a single sheet of parchment mounted using elastic polyester strips. 3D DIC is implemented to record in non-invasive and non-contact way the full-field response of parchment mock-ups to fluctuations of the relative humidity (RH) without interfering with the climatic chamber processes. We measure and compare the impact of fluctuating RH on unmounted and mounted parchment samples, through the full-field 3D measurements of dimensional changes at selected humidity levels, and through the local and global analysis of the samples’ response (displacement/strains) in time. We had proven in quantitative and detailed way that the applied mount fully fulfils its task, namely reduce significantly the out-of-plane displacements and strains occurring in the parchment during RH changes in the range from 39 to 80%. Our study also demonstrates the possibilities of using 3D DIC for the efficient support of conservation scientists in the development of storage, mounting, and treatment protocols for historical parchment.

Three-dimensional surface strain analyses of simulated defect and augmented spine segments: A biomechanical cadaveric study

While several studies have investigated fracture outcomes of intact vertebrae, fracture properties in metastatically-involved and augmented vertebrae are still far from understood. Consequently, this study was aimed to use 3D digital image correlation (3D-DIC) method to investigate the failure properties of spine segments with simulated metastatic lesions, segments augmented with poly(propylene fumarate) (PPF), and compare the outcomes with intact spines. To this end, biomechanical experiments accompanied by 3D-DIC were performed on spine segments consisting of three vertebrae and two intervertebral discs (IVDs) at loading rates of 0.083 mm/s, mimicking a physiological loading condition, and 200 mm/s, mimicking an impact-type loading condition such as a fall or an accident. Full-field surface strain analysis indicated PPF augmentation reduces the superior/inferior strain when compared with the defect specimens; Presence of a defect in the middle vertebra resulted in shear band fracture pattern. Failure of the superior endplates was confirmed in several defect specimens as the superior IVDs were protruding out of defects. The augmenting PPF showed lower superior/inferior surface strain values at the fast speed as compared to the slow speed. The results of our study showed a significant increase in the fracture force from slow to fast speeds (p = 0.0246). The significance of the study was to determine the fracture properties of normal, pathological, and augmented spinal segments under physiologically-relevant loading conditions. Understanding failure properties associated with either defect (i.e., metastasis lesion) or augmented (i.e., post-treatment) spine segments could potentially provide new insights on the outcome prediction and treatment planning. Additionally, this study provides new knowledge on the effect of PPF augmentation in improving fracture properties, potentially decreasing the risk of fracture in osteoporotic and metastatic spines.

Real-time 3D Digital Image Correlation for Large Deformation and Rotation Measurements Based on a Deformation Transfer Scheme

With the recent increase in digital image correlation (DIC) applications, it is important to improve the computational efficiency of DIC and realize the closed loop control of systems. A real-time three-dimensional (3D) DIC method for large deformation and rotation measurements is proposed in this paper. To solve the problem of initial guess estimation under large deformation and rotation, the convergence radius of the inverse compositional Gauss-Newton (IC-GN) algorithm considering large rotation and deformation is analyzed. Then, a temporal-spatial deformation transfer scheme is proposed for efficient temporal and stereo matching in 3D-DIC. The highly efficient IC-GN algorithm with an improved interpolation look-up table is proposed to further improve the computational efficiency. The multipoint and full-field real-time 3D deformation measurements are performed by parallel CPU computation. The convergence radius of IC-GN are estimated to be below 3 pixels for rotation and below 5 pixels for tensile deformation. The accuracy of the initial guess estimation by deformation transfer is improved and can meet the requirements of large deformation and rotation measurements. Benefiting from the temporal-spatial deformation transfer scheme, the efficient IC-GN algorithm, the efficient temporal and stereo matching strategy and the parallel computation, real-time multipoint deformation measurements at 60 Hz with 50 points and full-field deformation measurements at 15 Hz with 5000 points are realized. Real-time multipoint and full-field 3D deformation measurements for large deformations and rotations are realized. High-accuracy, real-time and fully automatic 3D deformation measurement sensors are expected.

Noncontact and Full-Field Measurement of Residual and Thermal Stress in Film/Substrate Structures

Residual stress and thermal stress of a film/substrate system are determined based on the curvature measurement with a 3D digital image correlation method (DIC) and calculation of the thin-film stresses by the extension of Stoney’s formula. A Ni film electroplated on a H62Cu plate is used to verify the proposed method. The full fields of nonuniform thin-film stresses are obtained in a room temperature to high-temperature environment of 200 °C, which can be potentially extended to higher temperatures. These results provide a fundamental approach to understanding thin-film stresses and a feasible measurement method for high temperature.

Ductile failure of flat plates containing two through-wall cracks: Experimental investigation and numerical modeling

Multiple cracks are frequently detected in structural components and should be assessed aimed to judge whether they can be treated as individual cracks or be combined to a larger crack. To study the ductile failure and crack interaction behavior, tensile tests using flat plates with two through-wall cracks were conducted, and 3D digital image correlation method (3D-DIC) was applied to acquire the displacement and full-field strain measurement. A damage evolution model integrated with a non-monotonic fracture strain locus was implemented to model the ductile fracture and crack interaction. Simulation results including load-displacement curves and predicted crack coalescence results fit well to the experiment data. Effects of mesh size and cut-off value of stress on the simulation results were investigated to ensure the accuracy of finite element analysis. The findings show that FE predictions using non-monotonic fracture strain locus are not only superior to those using monotonic ones, but also more accurate than alignment and combination rules in fitness-for-service codes.

Measurement of the Elastic Modulus and Residual Stress of Thermal Barrier Coatings Using a Digital Image Correlation Technique

This paper presents an experimental study on simultaneously measuring the elastic modulus and residual stress of a thermal barrier coating (TBC) after different isothermal heat treatments. The elastic modulus and residual stress of TBCs were theoretically analyzed based on composite beam bending theory. Thereafter, an experimental setup was established combining the 3D digital image correlation method with the bending test to obtain the curvature changes in the TBC sample. Finally, the elastic modulus and residual stress of the ceramic layer with different isothermal heat treatments were obtained. The results show that the elastic modulus of the ceramic layer measured under compression is greater than that under tension, and the elastic modulus of the ceramic layer increases first and then tends to be stable as the heat treatment time increases. In addition, the residual stress of the TBCs ceramic layer quickly changes from compressive stress to tensile stress with heat treatment, and the tensile stress increases with the increase in thermal exposure time. Furthermore, the reasons for the change tendency were analyzed according to the variation in porosity and microstructures by processing the scanning electron microscope (SEM) figures. The results demonstrate that simultaneously determining the elastic modulus and residual stress of TBC based on combining the 3D digital image correlation method with the bending test is effective and reliable.

Strain Field Calculation by 3D Digital Image Correlation Method Based on Subset Projection and Savitzky-Golay Filter

Strain Field Calculation by 3D Digital Image Correlation Method Based on Subset Projection and Savitzky-Golay Filter

Fracture toughness determination from load-line displacement of 3-point bend specimen using 3D digital image correlation method for CLF-1 steel

Load-line displacement (LLD) is essential for determining fracture toughness in terms of J-integral for nuclear structure materials. To obtain the accurate LLD, using a three-dimensional (3D) digital image correlation (DIC) method, the different LLD corresponding to different load points were measured on the miniature 3-point bend (3 PB) specimens of Chinese low activation ferritic/martensitic (CLF-1) steel in unloading compliance testing, and the load-displacement curves and J-integral determination were analyzed. The results show a higher LLD value generally derives a higher J-integral value. The J-integral values increase and then decrease with the distance from the top of specimen along crack direction, which is similar to the variation of LLD. It is interesting that the LLD of the load point almost at the neutral axis derive the peak J0.2(B) value (447 and 471 kJ/m2 at 250°C, 270 and 331 kJ/m2 at 450°C), close to the values (441 and 470 at 250°C, 269 and 332 kJ/m2 at 450°C) from the corresponding crack mouth opening displacement (CMOD). And the corresponding J0.2(B) values from LLD of points near the notch tip are much lower. The LLD of the load point at the neutral axis was recommended the accurate LLD to determine J-integral of the 3 PB specimens.