Image Correlation Method Research Articles

Integrated adaptive particle filtering-based color digital image correlation for large deformation measurement

In large deformation measurement, digital image correlation (DIC1Digital image correlation (DIC).1) using functional forms can no longer describe the complex changes in grayscale information and morphology of sub-regions. To address this issue, particle filtering (PF) can be combined with color DIC (PFDIC2Color digital image correlation method integrated with particle filtering. (PFDIC).2) to establish a color distribution model to describe sub-regions, but PFDIC has poor performance. Therefore, this paper proposes an integrated adaptive particle filtering-based color digital image correlation (APF-DIC3Integrated adaptive particle filtering-based color digital image correlation (APF-DIC).3). This method first constructs a dynamic color distribution model based on ACFEF4Adaptive color feature extraction function (ACFEF).4 to describe the sub-region. It then introduces the SSKL5Smoothed symmetric Kullback Leibler (SSKL).5 correlation coefficient to measure the similarity between sub-regions, and establishes TAR6Hyperbolic tangent adaptive resampling (tanh-adaptive resampling, TAR).6 to adaptively adjust the number of particles, ultimately achieving adaptive matching of sub-regions under complex deformations. Performance evaluation and simulation results show that APF-DIC significantly improves the accuracy, robustness, and computational efficiency of the algorithm. Real experimental results further verify the effectiveness of APF-DIC, demonstrating its excellent illumination invariance.

Improvement of the method of digital image correlation in the field of analyzing the processes of deformation and fracture of composites

The paper reflects new experimental results describing the processes of deformation and fracture of composites with significant structural heterogeneity with concentrators. A large-scale approach to the development of the method of digital image correlation (DIC) under complex modes of external influences is proposed. A number of methods of fixation of recorded data under cyclic impacts are considered. The peculiarities of each of the presented ways of data fixation depending on the main purpose of the research on the basis of static and cyclic tests of carbon fiber reinforced plastic specimens are outlined. Recommendations on the use of «analog capture» and «flex capture» options of the program «vic snap» are presented. The recommendations are valid for solving problems related to the analysis of regularities of deformation and fracture of objects with structural heterogeneity made of polymer composite materials under different modes of external loading. The study reflects the main methodological peculiarities arising when working with the non-contact optical video system VIC-3D and the method of correlation of digital images on polymer composite materials. Deformations at the structural and macroscopic levels are compared. Recommendations on the selection of post-treatment parameters, namely the step in the calculation by the KCI method, are proposed. A method of reducing the edge effect arising during uniaxial tensile testing of specimens with a concentrator is proposed. As a result of these studies, it becomes possible to obtain new experimental data on the processes of defect development and macroscopic fracture zones in the hole region, avoiding the influence of the edge zone.

The law of axial compressive damage of wood components with T-shaped and L-shaped cracks

ABSTRACT Wood components are easy to crack, which has great influence on their performance. So it is particularly essential to monitor and clarify the crack propagation law. In this paper, T- and L-shaped cracks were prefabricated on wood components, and acoustic emission (AE) and digital imaging correlation (DIC) technology were combined to monitor and analyse the damage of wood components under axial compression. The effects of different crack types on the damage forms, mechanical properties, damage index and propagation characteristics of acoustic emission signals were studied. It shows that the damage to L-cracked wood components was more serious than that of T-cracked wood and the acoustic emission signal strengthened as the load increased and the degree of rupture intensified. By establishing the corresponding relationship between the initiation and propagation behavior of wood microcracks and the acoustic emission parameters and surface strain, a measurement and evaluation system for in-situ monitoring the crack damage evolution of wood components with parallel and transverse cracks based on acoustic emission technology and digital image correlation method was successfully constructed. The test results provide a reference for further study on the damage mechanism and in-situ monitoring method of crack evolution behavior of wood with cracks.

Modeling the Stress Field in MSLA-Fabricated Photosensitive Resin Components: A Combined Experimental and Numerical Approach

This study presents an experimental and numerical investigation into the stress field in cylinders manufactured from photosensitive resin using the Masked Stereolithography (MSLA) technique. For material characterization, tensile and bending test data from resin specimens were utilized. The stress field in resin disks was experimentally analyzed using photoelasticity and Digital Image Correlation (DIC) methods, subjected to compressive loads, according to the cylinder–plane contact model. Images were captured during the experiments using polarizing film and a low-cost CPL lens, coupled to a smartphone. The experimental results were compared with numerical and analytical simulations, where the formation of fringes and regions indicating the direction and magnitude of normal and shear stresses were observed, with variations ranging from 0.6% to 8.2%. The convergence of the results demonstrates the feasibility of using parts produced with commercially available photosensitive resin on non-professional printers for studying contact theory and stress fields. In the future, this methodology is intended to be applied to studies on stress in gears.

Digital Image Correlation and Reliability-Based Methods for the Design of Structural Beams Made from Recycled Concrete Using Aggregates from Precast Rejects

The use of recycled aggregates in the manufacture of concrete is presented as a solution to reduce the consumption of resources and waste in the construction sector and contribute to a lower environmental impact. This work aims to explore the possibility of producing structural beams from recycled concrete using aggregates from precast concrete rejects and to improve their design using advanced characterisation techniques. To this end, the experimental data coming from mechanical test and the use of the digital image correlation approach are combined with a robust reliability-based method. The full-field data provided by the digital image correlation approach allow to determine the probabilistic density functions of the mechanical data. From these data, a predictive analysis of the maximum strength and deflection of flexural beams is carried out based on robust design techniques. This approach uses analytical theoretical models and a Monte Carlo-based simulation strategy that allows the prediction of the behaviour of the beams. This methodology was validated by manufacturing six beams with the previously analysed recycled concrete, HA-30, and testing them in the laboratory. All the beams showed behaviour within the predicted range: around 49.7 kN maximum load and just over 9.3 mm maximum deflection. These results demonstrate the robustness of the approach as well as the feasibility of using precast rejects for the manufacture of structural elements.

Evaluation of 3D-Printed Connectors in Chair Construction: A Comparative Study with Traditional Mortise-and-Tenon Joints.

The present paper investigates the possibility of replacing the traditional L-type corner joint used in chair construction with a 3D printed connector, manufactured using the Fused Filament Fabrication (FFF) method and black PLA as filament. The connector was designed to assemble the legs with seat rails and stretchers, and it was tested under diagonal tensile and compression loads. Its performance was compared to that of the traditional mortise-and-tenon joint. Stresses and displacements of the jointed members with connector were analyzed using non-linear Finite Element Method (FEM) analysis. Both connector and mortise-and-tenon joint were employed to build chair prototypes made from beech wood (Fagus sylvatica L.). Digital Image Correlation (DIC) method was used to analyze the displacements in the vicinity of the jointed members of the chairs. Seat and backrest static load tests were carried out in order to verify if the chairs withstand standard loading requirements. Results indicated that the 3D printed connector exhibited equivalent mechanical performance as the traditional joint. The recorded displacement values of the chair with 3D-printed connectors were higher than those of the traditional chair reaching 0.6 mm on the X-axis and 1.1 mm on the Y-axis, without any failures under a maximum vertical load of approximately 15 kN applied to the seat. However, it successfully withstood the loads for seating and backrest standard tests, in accordance with EN 1728:2012, without any structural failure. This paper presents a new approach for the chair manufacturing sector, with potential applicability to other types of furniture.

Microstructure and mechanical properties of the wire arc additively manufactured 316L/ER70S-6 bimetal structure

ABSTRACT The wire arc additive manufacturing (WAAM) process often begins printing on a substrate. In some cases, the substrate could act as a functional part of the WAAM-fabricated parts. In this work, ER70S-6 is directly deposited onto a 316L substrate using the WAAM process. Microstructural studies reveal good fusion and bonding at the interface. Due to the dilution of ER70S-6 and 316L, a gradient change in composition and microstructure was observed in the first six layers. The first layer (Fe-10Cr-5.5Ni-1Mo-1Mn) and the second layer (Fe-4Cr-2Ni-1Mn-0.5Mo) exhibit a bainite microstructure. Ferritic grains were observed from the third layer onwards. The microhardness is high at 336.9 ± 6.3 HV for the first layer and 302.7 ± 5.7 HV for the second layer. A decrease in microhardness was observed with the increase of the building layer until layer six. The yield strength is 356.6 MPa and the UTS is 502.3 MPa for the 316L/ER70S-6 bimetal joint. The digital image correlation (DIC) method is used to analyse the deformation behaviour. During the tensile test, the 316L substrate side yields first, and then the deformation shifts to the ER70S-6 side. This study also holds the potential for the development of novel alloys.

Strategy To Enhance Interfacial Properties: Preparation of Porous Polytetrafluoroethylene Fibers and the Adsorption of Initiators/Curing Agents.

Polytetrafluoroethylene (PTFE) fibers exhibit high inertness and demonstrate limited interfacial bonding capabilities with other materials. To overcome this limitation, PTFE@ZnO fibers were developed by depositing the porous ZnO layer onto PTFE fibers via a hydrothermal reaction, and porous fibers were adsorbed curing agents or initiators. The interfacial shear strength (ILSS) of the composites demonstrated a significant improvement, particularly in the case of composites containing PTFE/initiator fibers, where the ILSS increased by 104.8% compared to PTFE alone (from 8.3 to 17.0 MPa). The digital image correlation (DIC) method revealed a more uniform stress distribution in the modified fiber composites at the point of fracture. Additionally, nanoscratch tests indicated a significant enhancement in the interfacial bonding between the modified fibers and the resin. The porous structures facilitated mechanical interlocking between the modified fibers and the resin. Furthermore, the presence of an adsorbed initiator/curing agent within the porous structure served as the initiation site for the free radical polymerization of vinyl ester resin 901, thereby enhancing the interfacial bonding between the modified fibers and the resin. The novel strategy presents a general and viable approach for the extensive modification of PTFE fibers, focusing on achieving exceptional interfacial bonding properties.

Parameterized ZNCC image correlation for rotary-angle measurement

Abstract High-accuracy rotary-angle measurement is critical for precise positioning and control of robots, machine arms, and machine tools in industry. Image-based measurement is a very promising technology for angle positioning owing to its simple system, low cost, and good robustness to environments. Image correlation, such as the zero-mean normalized cross correlation (ZNCC) method, can obtain high accuracy image-positioning results, but their efficiency is too low to directly use in industries. This paper proposes to measure the absolute rotary angle using a parameterized ZNCC (PZNCC) image correlation method. The PZNCC expresses the ZNCC coefficient by the image shift parameters explicitly, so that the precise-match point corresponding to the global ZNCC maximum can be efficiently obtained and no image-resampling process is required. As a result, PZNCC is approximately 5 times faster than the classic inverse compositional Gauss–Newton (IC-GN) algorithm. Experiments show that rotary angle measurement based on PZNCC can obtain absolute angle positions with an accuracy of 1.16 arcsec (RMSE).

The Impact of Metrics in Mechanical Imaging

ABSTRACTOptical flow (OF) is an alternative technique to the more classical digital image correlation (DIC) methods, able to measure the motion between two images. It is a pixel‐wise method, in the sense that the displacement is defined at each pixel and its computation does not require overpixel grids. This paper examines the impact on the identified strain field, the main quantity of interest for solid mechanics, of the metrics used to quantify the conservation of the OF and to impose the regularity of the displacement. The Charbonnier and Lorentzian loss functions are inspected in this work. A new regularization approach is used to locally vary the Tikhonov parameter using a mask in order to preserve the discontinuities and encourage the appearance of local phenomena while smoothing the computed fields elsewhere. Finally, an open‐source GPU‐accelerated python code has been implemented.

Macro–Micro Failure Characteristics of Soft–Hard Composite Rock with Unparallel Joints: Analysis Based on DIC and AE Technique

Jointed composite rock masses are ubiquitous, where the interplay between fractures and bedding planes significantly complicates their failure mechanisms. This study conducted uniaxial compression tests on a composite rock material featuring soft and hard components with unparallel double joints. Leveraging the digital image correlation (DIC) method and acoustic emission (AE) technology, the investigation analyzed the influence of joint angles on the mechanical properties, failure modes, and crack propagation behaviors. The results indicate that the peak strength exhibits an ascending–descending–ascending trend with the variation of upper joint angle, peaking at 90°. The failure modes can be systematically categorized into three types. The failure of the specimen is predominantly influenced by the upper joint. However, when the lower joint angle is relatively flat, it becomes more prone to contributing to the failure of the specimen. The lower joint-dominated failure mode only occurs when the upper joint angle is 90°. As the lower joint angle remains at 90°, an augmentation in the upper joint angle initially leads to a decrease and subsequently to an increase in the proportion of shear cracks. In contrast, when the lower joint angle deviates from 90°, the increase of the upper joint angle initially boosts and then diminishes the proportion of shear cracks.

Failure Behavior of Nano-Metakaolin Concrete Under Splitting Tension Based on Digital Image Correlation Method.

Nano metakaolin (NMK) has attracted considerable interest for its potential to improve the durability of cementitious materials. However, the effect of NMK on the splitting tensile performance of concrete has not been systematically investigated. This study investigates the splitting tensile performance of NMK concrete and analyzes its failure behavior under splitting load. Different NMK dosages (0%, 1%, 3%, 5%, and 7%) were considered, and splitting tensile tests were conducted. The crack propagation process, crack width, and crack growth rate on the surface of NMK concrete during the splitting tensile test are analyzed using the Digital Image Correlation (DIC) method. The mechanisms by which NMK affects the splitting tensile performance of concrete were examined using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), and Thermogravimetric Analysis (TG). The results indicate that the incorporation of NMK enhances the splitting tensile performance of concrete. Concrete with 5% NMK addition exhibited the highest splitting tensile strength, with an increase of 17.4% compared to ordinary concrete. NMK improved the cracking resistance and overall integrity under splitting tensile load. With 5% NMK addition, the surface crack length, width, and main crack propagation rate of the concrete decreased by 4.5%, 35.3%, and 29.6%, respectively. NMK contributed to a denser internal structure of the concrete, promoted the formation of C-S-H gel, and increased the degree of cement hydration. Moreover, a lower thickness and Ca/Si ratio of interfacial transition zone (ITZ) were observed in NMK concrete. The ITZ thickness and Ca/Si ratio of concrete with 5% NMK were reduced by 64.4% and 85.4%, respectively, compared to ordinary concrete. In summary, the influence mechanism of NMK addition on the splitting tensile strength and failure behavior of concrete is explored in this study, providing experimental data to support the application of NMK concrete in practical engineering.

Stereo digital image correlation using binocular super-resolution

Abstract The spatial resolution and measurement accuracy of the digital image correlation (DIC) method are constrained by camera resolution. This limitation is primarily determined by hardware costs. However, in current stereo DIC measurements, only the gray level or its gradient from two images is used for integer-pixel matching and sub-pixel optimization. It implicitly treats the two images from different viewpoints as independent entities before correlating them. However, the inherent structural information has not been fully utilized. This previously overlooked structural information provides a novel approach to enhancing the accuracy of DIC by leveraging the inherent correlations between stereo image pairs. The realization of binocular super-resolution typically requires a relatively small parallax. Moreover, the DIC method can achieve image window pairing with small parallax through pre-matching. This implies that binocular super-resolution and Stereo-DIC can complement each other by sharing information. In this paper, the DIC method is employed for whole-pixel image matching, while the binocular super-resolution method, based on deep learning, is applied to process the matched image pairs. Building on previous experiments, extensive datasets containing diverse experimental scenes and various speckle patterns were compiled and utilized. Furthermore, the DIC method can establish training datasets with minimal parallax through integer-pixel matching, thereby achieving highly effective super-resolution results. Experimental results demonstrate that super-resolution images with a higher signal-to-noise ratio can be obtained. Additionally, it effectively provides more image details, which enhance the calculation accuracy and resolution of DIC.

Assessment of the fracture properties of mortars reinforced with synthetic fibers

AbstractThis paper investigates the post‐cracking behavior of mortars reinforced with synthetic polypropylene fibers. To three series of mortars, normal strength (NSM), high strength (HSM), and high strength with fly ash (HSMFA), short and long, was introduced at 0.6% and 1% by volume, respectively. Pre‐notched 4 × 4 × 16 cm were used for 3‐point flexural tests, and the digital image correlation (DIC) method was employed to assess the load‐CMOD curves. Based on the experimental curves, a tri‐linear stress‐crack opening (σ‐w) relationship was used to develop an analytical model for the Mode I crack propagation, and the inverse analysis method was applied to optimize the model's parameters. The obtained parameters were compared to the fib MC2010 characteristic values related to serviceability and ultimate limit states. The results show that short fiber‐reinforced mortars exhibit a softening behavior regardless of the fiber dosage after a rapid drop once the tensile strength has been achieved. The three mortars incorporating long fiber reinforcement exhibit a very high deformation capacity and hardening behavior. For NSM, fibers appear to be more effective than HSM and HSMFA. All materials achieve the ultimate fracture opening of 2.5 mm, as defined by the fib MC2010, except 0.6% long fiber‐reinforced HSMFA. Compared to the reference mixture (mixture without fibers), adding synthetic fibers to the mortar did not exhibit a significant environmental and health impact.

Dynamic tensile properties of thermally treated concrete specimens subjected to varied heating rates: an investigation using the digital image correlation method

Dynamic tensile properties of thermally treated concrete specimens subjected to varied heating rates: an investigation using the digital image correlation method

Experimental study of propellant/liner interface fracture characteristics

Abstract The propellant/liner interface debonding is one of the main failure modes affecting the structural integrity of solid rocket motors. In order to study the mechanical properties of the propellant/liner interface, the Double-Cantilever Beam (DCB) specimen of the propellant/liner interface was improved. Based on the propellant/liner interface DCB specimens, tensile tests at different temperatures and loading rates were carried out. Based on the digital image correlation(DIC) method, the strain field of the whole DCB specimen and the propellant part was analyzed respectively. Meanwhile, the fracture morphology of DCB specimen was analysed. The results show that the improved specimen can effectively characterize the properties of the propellant/liner interface. The propellant/liner interface shows obvious temperature and strain rate dependence, and the effect of temperature on the propellant/liner interface performance is more significant than that of loading rate. The deformation at the propellant/liner interface of the DCB specimen can reach about 50%, and the interface fracture mode of propellant/liner is cohesive fracture.

A robust feature-based full-field initial value estimation in path-independent digital image correlation for large deformation measurement

The feature-based path-independent digital image correlation (DIC) method has been shown to be a formidable tool for non-contact, full-field measurement of large deformation, but its effectiveness hinges crucially on acquiring sufficient matched features to perform a reliable full-field initial value estimation (IVE) for all points of interest (POIs), thus ensuring their successful and rapid convergence in the succeeding path-independent iterative DIC refinement. This prerequisite is a challenging task particularly when confronted with large deformation. Moreover, in many real-world measurement scenarios, the accuracy of IVE is also influenced by image noise, such as Gaussian noise and shot noise, further compounding the challenge. To mitigate these issues, we propose a robust feature-based full-field IVE method. The core of this method consists of two main components: (i) For feature detection, we leverage the strengths of nonlinear multiscale representations on speckle images using an Accelerated-KAZE (A-KAZE) detector, which extracts features in a nonlinear scale space via nonlinear diffusion filtering. Noise is suppressed and edges are preserved. Compared to existing state-of-the-art feature detectors used in DIC, such as Scale Invariant Feature Transform (SIFT) and Speeded-Up Robust Feature (SURF) detectors, which rely on the use of Gaussian linear scale spaces, the A-KAZE-based nonlinear scale space detector identifies more salient features with higher localization accuracy. (ii) For feature description, considering the need for robustness against large deformation and the computational burden of descriptor matching for considerable salient features that may be detected in speckle images, we introduce a robust Gradient Location and Orientation Histogram (GLOH) descriptor and propose an improved version of it. The GLOH's improved version incorporates a restricted adaptive binning (RAB) strategy to optimize the descriptor’s structure parameters, which is able to reduce the computational cost of descriptor matching through restricting its dimensionality while without sacrificing its robustness and discriminability. These two components are designed to provide sufficient matched features for a full-field IVE. The initial deformation for each POI is estimated independently by fitting a local affine transformation model, which is refined to subpixel accuracy through iterative path-independent DIC analysis. To handle complex large deformation, the inverse compositional Gauss-Newton (IC-GN) algorithm with a second-order shape function is employed. Extensive experimental results demonstrate that our method has improved IVE accuracy as well as behaves more robustness against local geometric transformations and image noise including Gaussian noise and shot noise, as compared to existing state-of-the-art feature-based full-field IVE methods.

Influence of flake graphite coated MgO particles on thermal shock resistance and fracture behaviour of MgO-C refractories based on Brazilian splitting test with digital image correlation method and acoustic emission technique

Influence of flake graphite coated MgO particles on thermal shock resistance and fracture behaviour of MgO-C refractories based on Brazilian splitting test with digital image correlation method and acoustic emission technique

Experimental investigation on in-plane shear behavior of E-glass fiber/epoxy laminated composites under different strain rates

Glass fiber reinforced polymer (GFRP) has been widely applied in buildings and bridges owing to its excellent material properties. The GFRP as a bearing load component in structures may be damaged, with an increasing threat from accidental impact. To understand the dynamic in-plane shear properties of GFRP is essential, which is a basis to design and evaluate structures. In this study, the ±45° specimens of GFRP laminated were tested to investigate the in-plane shear properties with the strain rate from quasi-static to 106 s−1. The dynamic test was conducted by INSSTRON VHS and the stretch process was record by high-speed camera. The Digital Image Correlation (DIC) method was used to obtain strains of the specimens. And the field-emission scanning electron microscopy (SEM) technique was used to observe the fracture surface of the specimen. The results indicated that the failure mode, shear strength, failure strain, failure strain, absorbed energy and shear modules possessed strain rate effects. Furthermore, the empirical equations were proposed, which can be used to predict the dynamic increase factor at different loading rate.

Research on Compression Failure Characteristics and Damage Constitutive Model of Steel Fiber-Reinforced Concrete with 2% Copper-Coated Fibers Under Impact Load.

This study systematically investigates the mechanical properties of plain concrete (PC) and 2% steel fiber reinforced concrete (SFRC) under both static and dynamic loading conditions, utilizing advanced mechanical testing equipment and dynamic impact testing methods. The strain rate range studied spans from 10-4 s-1 to 483.12 s-1. Under static loading conditions, the maximum bearing capacity and energy absorption capacity of 2% SFRC are 2.16 times and 3.83 times greater than those of PC, respectively, indicating a significant enhancement in toughness and resistance to failure. Under dynamic loading conditions, the energy absorption capacity of SFRC increases to 6.36 times that of PC. The impact failure behavior of SFRC was analyzed using the split-Hopkinson pressure bar-digital image correlation (SHPB-DIC) method, revealing that the failure was primarily driven by splitting tension. The failure process was subsequently categorized into four distinct stages. At high strain rates, the dynamic enhancement factor, peak stress, and peak strain of SFRC exhibit a linear increase with strain rate, whereas the energy absorption capacity increases in a nonlinear manner. This study presents a simplified viscoelastic constitutive model with four parameters and develops a damage-based viscoelastic constitutive model with seven parameters, demonstrating its broad applicability. The findings offer both theoretical insights and experimental evidence to support the use of SFRC under high strain rate conditions.