Three-dimensional Digital Image Correlation Research Articles

3D-DIC analysis for BIM-oriented SHM of a lab-scale aluminium frame structure

In recent years, three-dimensional Digital Image Correlation (3D-DIC) has proven to be a reliable technique for Structural Health Monitoring (SHM) by allowing full line-of-sight, high-resolution, and contactless measurements of structures. The large amount of raw output resulting from 3D-DIC requires appropriate methods to visualise and analyse the data systematically. In this context, Building Information Modeling (BIM) emerges as a robust repository and data management tool to store, query, and assess long sequences of SHM data. Different sensors have been used to collect SHM data and digital sensors have been created in the BIM environment to mimic the behaviour of the physical ones on site. This research focuses on the BIM implementation of virtual sensors from information retrieved using 3D-DIC to store frequency and time domain data and monitor structural changes in a targeted system over time. The application of the Phase-based Motion Magnification (PMM) technique is proposed as a preprocessing tool for 3D-DIC analysis videos to obtain displacement information in specific frequency bands and make those values structurally effective. As a case study, a three-story aluminium frame structure with a damaged and undamaged configuration is used to validate the developed methodology.

Energy balance of rapidly deforming foam filled cylindrical shells in a high pressure fluid environment

The pressure differential between an air-filled structure and the surrounding fluid for underwater applications can potentially lead to instabilities and collapse of the structure. When air-filled structures collapse underwater, large pressure pulses are emitted into the surrounding water, which can damage nearby living organisms and structures. The present study aims to mitigate the high-pressure spikes generated in underwater implosions. Experiments were performed underwater in a pressure vessel. Thin-walled aluminum 6061 cylindrical shells were placed in the water filled pressure vessel, and the hydrostatic pressure was increased until the tubes reached instability and subsequently collapsed. To mitigate the pressure pulses radiated into the fluid by the implosion of the tubes, closed cell polyvinyl chloride foam rods of varying densities were placed inside of the aluminum tubes and assembled concentrically. The densities of the solid foam rods were 45 and 100 kg/m3, which were selected to investigate the effect of foam density on the mitigation capabilities of the foam rods. Three-dimensional digital image correlation was coupled with high-speed photography to obtain the full-field displacements and velocities of the aluminum tubes during implosion. Moreover, the pressure fields created during the structural collapse of the tubes were recorded with tourmaline pressure transducers. The 45 kg/m3 foam reduced the peak pressure pulse generated during the implosion event by 30%, whereas the 100 kg/m3 foam rods reduced the peak pressure pulse by 50%. Furthermore, the 45 kg/m3 foam decreased the energy imparted onto the fluid by the implosion of the tubes by 16%, whereas the 100 kg/m3 foam decreased the energy imparted onto the fluid by the implosion by 43%. Full field displacement data showed that both foam densities reduced the radial velocity of the tube during implosion, as well as reducing the peak centerpoint decelerations of the tube prior to wall contact by 45% and 62% for the 45 kg/m3 and the 100 kg/m3 foam, respectively. Fully coupled fluid–structure interaction finite element models were created using the Abaqus software to obtain the structural deformation energy in the aluminum tubes after implosion, as well as the energy absorbed by the foam rods. The models were in good agreement with the experiments in terms of radial displacements during implosion, as well as the final foam rod volume.

Structural Integrity Assessment of Defected Gas Pipelines Using a Simplified Ductile Damage Model

Abstract The finite element method using the damage model has been increasingly used to predict the failure of various structures. Thus, various damage models were presented, and recently, a phenomenological model called the local fracture strain model was presented, making it easy and accurate to predict the damage of the structure. This model has the advantage of defining fracture strain as a function of stress triaxiality with only a few notched tensile tests but has a limitation because it does not consider the damage evolution because of the void growth. This study presents an enhanced damage model that improves the accuracy of the failure simulation of defected structures by adding a parameter that considers stiffness degradation according to void growth to the damage model based on the fracture strain. Therefore, loading–unloading tests were conducted and the damage index of fracture was identified using a three-dimensional digital image correlation system. The failure simulation results using the proposed damage model were compared with experimental, such as notched tensile, single edge notched tension (SENT), and full-scale burst tests.

Quantitative evaluation of the severity of wrinkles in carbon fiber composites

A new method combining three-dimensional digital image correlation (3D-DIC) with a novel numerical framework was proposed to evaluate the severity of wrinkles in composite laminates. In this numerical framework, the micromechanics model of wrinkles based on a two-step homogenization technique was embedded in three-dimensional finite element method (FEM). The influence of waviness ratio (the ratio of wrinkle amplitude to wavelength) and stacking sequence on mechanical behaviors of wrinkled laminates under axial tension load was studied. Numerical results showed that the out-of-plane displacement in the vicinity of wrinkle zones obviously increases by 10%–20%. The simulation was then verified by experimental observations.

Real-time localization of micro-damage in concrete beams using DIC technology and wavelet packet analysis

As the service time of large civil engineering structures increases, structural health monitoring providing early warning information becomes increasingly important. In this study, three reinforced concrete beams were poured as specimens, and four-point bending experiments were conducted to investigate the localization of the micro-damage of the specimens. Three-dimensional digital image correlation (DIC) technique was employed to acquire and handle the images of changes in the surface of the specimens under various loads during the experiment. Then, Daubechies wavelet with 3 layers and order N of 10 was utilized to extract the energy spectrum of the principal strain nephogram obtained by DIC. The energy change rate (ECR) and energy change rate standard deviation (ECRSD) were defined and selected as micro-damage identification indicators. Then the ECR and ECRSD were calculated in full-filed and partial-field respectively with the energy spectrum acquired by Daubechies wavelet. Finally, a calculation process with detailed steps was proposed to realize the real-time location and observe the development of micro-damage on the surface of specimens. The accordance of calculation results and experimental results illustrates that the coupled strategy between DIC and Daubechies wavelet method is powerful in the real-time location of micro-damage on the concrete structure. The findings of this study could provide an effective and feasible method for structural health monitoring.

Effect of thermal treatment on the fracture toughness and subcritical crack growth of granite in double-torsion test

An understanding of the fracture behavior and subcritical crack propagation of hard rock under different temperatures is necessary for the design and stability of nuclear waste disposal projects. The aim of this study was to understand the thermal effect on the fracture behavior of granite, which had been heated at 25 (untreated), 100, 200, 400, and 600 °C, respectively. A series of uniaxial compressive tests and double-torsion tests were performed on granite specimens. The three-dimensional digital image correlation technique was used to investigate the strain evolution and fracture pattern in granite specimens during subcritical crack propagation. According to the results, the uniaxial compression strength, Young’s modulus and fracture toughness of the granite specimens increased and then decreased with an increase in treatment temperature. These parameters dropped sharply as the treatment temperature exceeded 400 °C, mainly because of the thermally-induced destruction of the quartz crystal structure and a generation of wider intergranular fractures. A comparison of the subcritical crack length by theoretical calculations and experimental observations from digital image correlation showed that the two values were consistent. At a treatment temperature of 400 °C and 600 °C, the velocity of the subcritical crack propagation was accelerated, so the length of the subcritical crack during the relaxation test was 4.14 times and 5.25 times that at 25 °C, respectively. The subcritical crack growth and fracture process of the double-torsion tests were visible by the three-dimensional digital image correlation system. A subcritical crack growth index (n) can be used to characterize the susceptibility of the subcritical crack propagation in rock relaxation tests, which helps to evaluate the long-term stability of nuclear waste disposal projects.

Study on mechanical properties and failure mechanism of 18650 Lithium-ion battery using digital image correlation and acoustic emission

The safety of lithium-ion batteries (LIBs) remains the focus of engineering and scientific attention as its bending failure cannot be monitored by conventional means such as voltage and temperature due to its special failure mechanism. Therefore, it is of great significance to study the mechanical properties and failure mechanisms of LIBs during bending failure. In this paper, 18,650 LIBs are taken as the research object, and an in-situ experimental platform based on acoustic emission (AE) and three-dimensional digital image correlation (3D-DIC) methods is built to study the mechanical properties and failure mechanisms of LIBs in different states of charge (SOC) under bending loads. The results show that the bending modulus and stiffness of the battery increase with the increase of SOC. The main types of damage and the expansion process of the battery during the bending failure process are also obtained. The research results provide a theoretical basis for research on the bending failure of LIBs. Meanwhile, the experimental platform built in this article solves the failure of previous monitoring methods, including deformation and temperature during the bending failure of LIBs. In addition, this paper provides a new method for in-situ monitoring of LIBs.

Dynamic mechanical properties and fracturing behaviour of concrete under biaxial compression

Heterogeneity is an important factor affecting the dynamic mechanical properties and failure process of geomaterials especially when considering the coupled effect of strain rates and confinements. In this research, dynamic biaxial compression tests are conducted on concrete by using a triaxial Hopkinson bar system with different biaxial confinements (i.e., pre-stress σ1 and σ2: 5–30 MPa) and impact velocities (i.e., 14–18 m/s corresponding to strain rates of 80-140 s-1). High-speed three-dimensional digital image correlation (3D-DIC), synchrotron-based micro-computed-tomography (micro-CT) and a machine learning-based crack classification technique are adopted to quantify the dynamic deformation and fracturing properties. Experimental results show that both dynamic strength and peak strain decrease with increasing axial pre-stress σ1, but increase with higher lateral pre-stress σ2 and impact velocity. Fractures generally propagate from the surfaces of the specimen towards the centre along the impact direction, and appear at interfaces and in the matrix first and aggregates afterwards. Real-time surface deformation and post-failure fractures are aggravated with pre-stress σ1 and impact velocity, but restrained by pre-stress σ2. Statistical crack analysis indicates that different crack types (e.g., matrix crack, interfacial crack and transgranular crack) own distinct geometrical characteristics (e.g., orientation distribution, fractal dimension and position distribution) and are affected by the orientation and aspect ratio of aggregate. Moreover, transgranular crack ratio decreases with higher pre-stress σ1, but increases with larger pre-stress σ2 and impact velocity, consistent with variation of total stress and fracture energy, implying the significance of transgranular crack on mechanical properties and fracture energy of heterogeneous geomaterials under dynamic loadings.

Strain monitoring of wind turbines using a semi-autonomous drone

In this work, an approach is proposed that can perform a nondestructive evaluation of wind turbine structures using a non-contact, three-dimensional full-field optical digital image correlation (DIC) technique. This approach can quantify the level of strain and loading conditions that rotating structures such as wind turbines experience during operation. The optical technique does not interfere with the structural functionality of the wind turbine. Moreover, the use of Unmanned Aerial Vehicles (UAVs) for remote inspection enables robust measurements for periodic inspection. The strain obtained using the proposed approach is validated using strain gauges mounted on the blades. A control algorithm is designed for the UAV to stabilized and obtain the desired field of interest and working distance based on the turbine size. Blending the benefits of the remote accessibility of UAVs and full-field dynamic evaluation of structures using strain data obtained with DIC is a novel method of monitoring wind turbines.

Residual compression property and response of honeycomb sandwich structures subjected to single and repeated quasi-static indentation

Abstract This paper investigated the response and residual compression properties of honeycomb sandwich structures subjected to single quasi-static indentation (QSI) and repeated QSI (RQSI). The damage depth after repeated low-velocity impact (LVI) was considered as the governing parameter during the QSI experiments. Three-dimensional digital image correlation method was applied to determine deformation of the front panels after LVI and QSI to describe damage to honeycomb structures. For specimens with the same depth, it is found that the residual strength of QSI was less than that of LVI and close to that of RQSI. Results indicated that it is more reasonable to describe the damage by volume than by depth.

Comprehensive characterisation of the compressive behaviour of hydrogels using a new modelling procedure and redefining compression testing

The aim of tissue engineering is the regeneration of damaged tissue or the production of representative tissue organoids in vitro. To achieve this, one approach is to use hydrogels, water-swollen hydrophilic and crosslinked polymer networks, that can accommodate encapsulation of living cells and help the regeneration process. Even though mechanically biomimicking target tissue is important for a favorable cell response, the mechanical characterisation of tissues or hydrogels is not yet a fully defined process with various possible models and methods existing. In this paper, for the first time, a specific procedure and model has been suggested for the discussion of the nonlinear stress-strain relationship in large deformations of hydrogels. Moreover, this approach has comprehensively characterised the compressive material performance of hydrogels in a theoretical framework. To present the performance and utility of the introduced procedure, it is used with two different compositions of bioamine crosslinked gellan gum hydrogel. In addition, a three-dimensional digital image correlation technique has been utilized together with compression testing to measure the actual force and deformation in unconfined compression. The material model parameters were obtained to represent nonlinear stress-strain behaviour and the viscoelastic response (relaxation) of gellan gum hydrogel in compression.

Stereo-DIC Measurements of a Vibrating Bladed Disk: In-Depth Analysis of Full-Field Deformed Shapes

Vibration measurements of turbomachinery components are of utmost importance to characterize the dynamic behavior of rotating machines, thus preventing undesired operating conditions. Local techniques such as strain gauges or laser Doppler vibrometers are usually adopted to collect vibration data. However, these approaches provide single-point and generally 1D measurements. The present work proposes an optical technique, which uses two low-speed cameras, a multimedia projector, and three-dimensional digital image correlation (3D-DIC) to provide full-field measurements of a bladed disk undergoing harmonic response analysis (i.e., pure sinusoidal excitation) in the kHz range. The proposed approach exploits a downsampling strategy to overcome the limitations introduced by low-speed cameras. The developed experimental setup was used to measure the response of a bladed disk subjected to an excitation frequency above 6 kHz, providing a deep insight in the deformed shapes, in terms of amplitude and phase distributions, which could not be feasible with single-point sensors. Results demonstrated the system’s effectiveness in measuring amplitudes of few microns, also evidencing blade mistuning effects. A deeper insight into the deformed shape analysis was provided by considering the phase maps on the entire blisk geometry, and phase variation lines were observed on the blades for high excitation frequency.

Mechanical anisotropy of coal under coupled biaxial static and dynamic loads

Understanding the mechanical properties and fracturing behaviours of coal is significant for the safety of underground mining engineering. Coal failure characteristics are highly influenced by the anisotropy and loading conditions. In this study, the coupled biaxial static and dynamic tests are conducted on coal specimens with five bedding orientations θ (i.e., 0°, 30°, 45°, 60°, and 90°) with respect to the normal direction to loading. A Triaxial Hopkinson bar (Tri-HB) system is adopted to apply the biaxial quasi-static stress first and then dynamic loading at four impact velocities (i.e., 10, 13, 17, and 21 m/s). Real-time processes of coal fracturing are recorded by two high-speed cameras, and accordingly, full-field deformation and ejection velocities are identified by the three-dimensional digital image correlation (3D-DIC) technique. Moreover, the internal fracture morphology of coal specimens is characterised using synchrotron-based X-ray computed tomography (CT). Experimental results show that at similar strain rates, the peak stress against θ shows a “U” shape with the lowest value at θ = 60°. The peak stress increases with increasing impact velocity, while its growth rate exhibits a downward trend revealing a decreasing sensitivity to strain rate. Coal ejection velocities are positively rate-dependent, and the highest ejection velocity is found shifting from θ = 45° to θ = 90° with increasing impact velocity. The average fragment size of coal specimens is negatively related to impact velocities and energy absorption, and the finest fragmentations are observed at around θ = 45°. Dynamic behaviours of coal under biaxial pre-stresses are dependent on bedding structures and strain rates, while the bedding effect becomes weak as strain rate increases.

Quasi-static and low-velocity impact biaxial flexural fracture of aluminosilicate glass — An experimental and numerical study

In this study, the quasi-static biaxial fracture behavior of aluminosilicate glass is investigated via Ball-On-Ring (BOR) and Ring-On-Ring (ROR) tests aided by a three-dimensional Digital Image Correlation (3D-DIC) technique. In-plane strain field and out of plane deformation distribution during the loading process can be obtained by this test system, overcoming the problem of inaccurate displacement data provided by the loading machine. During the loading process, a uniform strain distribution field is formed below the load ring of the ROR specimen while a gradient strain distribution is built for the BOR specimens. For dynamic loading conditions, low-velocity impact BOR tests are conducted at velocities of 2 m/s and 4 m/s showing a dynamic strengthening effect and high-speed cameras provide detailed fracture and failure sequences of the glass plates. Finite Element Method (FEM) simulations with the JH-2 material model are carried out showing good consistency with experimental results for the quasi-static loading conditions. FEM coupled to Smooth Particle Hydrodynamics (FEM-SPH) technique is utilized for dynamic simulations to solve the element distortion and non-physical problems. The influence of the tensile strain rate effect on low-velocity impact behavior of aluminosilicate glass is analyzed in detail. The original JH-2 model does not provide a reasonable prediction of the dynamic tensile response of brittle materials and the model requires further modifications to describe the dynamic tensile fracture behavior. By introducing rate-dependence maximum hydrostatic tensile strength σt,max to the updated model, better predictions for the contact force and projectile residual velocity histories of low-velocity impact tests can be provided.

Experimental evaluation of carbon fibre, fibreglass and aramid tubular braided composites under combined tension–torsion loading

Braided composites are a class of composite materials that feature an inter-woven structure that improves structural stability and damage tolerance. Presently, braided composites under tension and torsion loading have been studied individually. Mechanical behaviour of braided composites under combined tension–torsion loading is common and therefore requires investigation. In this study, mechanical properties of carbon fibre, fibreglass and aramid 2D tubular braided composites (TBCs) were assessed and compared under coupled tension–torsion loading. The plane stress theory investigated the failure mechanism of braids. A contact-free three-dimensional digital image correlation (3D DIC) technique was used to derive detailed and continuous strain maps and understand the buckling behaviour of TBCs.

Effect of different preconditioning protocols on the viscoelastic inflation response of the posterior sclera

Preconditioning by repeated cyclic loads is routinely used in ex vivo mechanical testing of soft biological tissues. The goal of preconditioning is to achieve a steady and repeatable mechanical response and to measure material properties that are representative of the in vivo condition. Preconditioning protocols vary across studies, and their effect on the viscoelastic response of tested soft tissue is typically not reported or analyzed. We propose a methodology to systematically analyze the preconditioning process with application to inflation testing. We investigated the effect of preconditioning on the viscoelastic inflation response of tree shrew posterior sclera using two preconditioning protocols: (i) continuous cyclic loading-unloading without rest and (ii) cyclic loading-unloading with 15-min rest between cycles. Posterior scleral surface strain was measured using three-dimensional Digital Image Correlation (3D-DIC). We used five variables of characterizing features of the stress-strain loop curve to compare the two preconditioning protocols. Our results showed protocol-dependent differences in the tissue response during preconditioning and at the preconditioned state. Incorporating a resting time between preconditioning cycles significantly decreased the number of cycles (10.5 ± 2.9 cycles vs. 3.1 ± 0.5 cycles, p < 0.001) but increased the total time (15.8 ± 4.4 min vs. 51.2 ± 8.3 min, p < 0.001) needed to reach preconditioned state. At the preconditioned state, 2 of 5 characteristic variables differed significantly between protocols: hysteresis loop area (difference=0.023 kJ/m3, p = 0.0020) and elastic modulus at high IOPs (difference=24.0 MPa, p = 0.0238). Our results suggest that the analysis of the preconditioning process is an essential part of inflation experiments and a prerequisite to properly characterize the tissue viscoelastic response. Furthermore, material properties obtained at the preconditioned state can be impacted by the resting time used during preconditioning and may not be directly compared across studies if the resting time varies by 15 min between studies. Statement of significanceAlthough applying a preconditioning protocol by repeated cyclic loads is common practice in ex vivo mechanical characterization of soft tissues, the tissue response is typically not reported or analyzed, and the protocol’s potential effect on the response remains unclear. This is partially caused by lack of a standardized methodology to precondition soft tissues. We present the first systematic analysis of two representative preconditioning protocols used during inflation testing in ocular biomechanics. Our results show protocol-dependent differences in the viscoelastic response during the preconditioning process and at the preconditioned state. Consequently, the analysis of the preconditioning response represents an essential part of mechanical testing and a prerequisite to properly characterize the tissue viscoelastic response. The effect of preconditioning on the preconditioned state response must be considered when comparing results across studies with different preconditioning protocols.

Multiaxial deformation behavior of aluminum alloy 6061 subjected to fire damage

Aluminum alloy AA6061 is of interest to the US Navy for ship structure applications due to its light weight, ease of manufacturing, corrosion resistance and strength. However, response to complex loading subsequent to fire damage presents a concern for practical applications. The purpose of this study is to evaluate the effect of fire damage on the microstructure and material response of AA6061 with applied tensile, torsional, and combined loading. Fire exposure was simulated in a controlled environment and testing under multi-axial loading conditions was carried out on virgin and fire damaged samples to evaluate mechanical response. Because of the non-circular sample cross-section, a three-dimensional digital image correlation technique was used to capture the evolution of local strains over the gage length of a deforming specimen subjected to tensile and/or torsional loading. Additionally, microstructure was investigated by electron backscatter diffraction at target cross-section locations subsequent to fire exposure and/or mechanical testing. Results indicate a 60–70% strength reduction with fire exposure. Fire exposed samples achieved higher maximum tensile load during combined loading compared to pure tensile loading. Microstructure was relieved by fire exposure while mechanical loading reveals strain-induced grain refinement. With sample geometry leading to stress concentrations, a deviation from yield values predicted by conventional yield criteria was observed; multi-axial stress-strain data can be of help in assessing the state of aluminum alloy structures after fire exposure.

Experiments on a Thin Panel Excited by Turbulent Flow and Shock/Boundary-Layer Interactions

An experimental methodology was designed to study the effects of turbulent flow and shock/boundary-layer interaction (SBLI) on the postflutter response of a thin, buckled panel. The approach combines a systematic testing strategy with state-of-the-art full-field, noncontact measurement techniques, including pressure-sensitive paint, three-dimensional digital image correlation (DIC), and schlieren imaging. These measurements, combined with traditional sensors, were used to characterize the loading conditions and the structural response. The thermally buckled panel experienced bistable, cross-well oscillations with cavity pressure modulation for turbulent flow conditions. This response was characterized as chaotic using several conventional criteria. As the temperature differential between the frame and panel decreased, the panel response transitioned to periodic. For the first time, shock-induced limit cycle oscillations (LCOs) were also measured using DIC. In the presence of an attached SBLI, the dynamic response was centered about the three-quarter chord. As the strength of the SBLI increased, the LCO initially subsided and then reappeared near the midchord for the strongest shock considered.

In-plane shear response of a composite hexagonal honeycomb core under large deformation – A numerical and experimental study

In the present work, experimental shear tests using a custom-built picture-frame shear fixture have been conducted to investigate the in-plane pure-shear response of an HRP-C fiberglass/phenolic hexagonal honeycomb core under large deformation. Three-dimensional digital image correlation was used during the quasi-static tests to measure the homogenized surface strain fields in the core specimen. A new hyperelastic orthotropic material model was developed to capture the in-plane finite strain behavior of the honeycomb core. The picture-frame shear test on the core was simulated numerically using the homogenized material model, and predictions were compared with test data. Unlike the Hookean orthotropic material model, which exhibited softer responses in comparison to test data, good agreement was observed between the hyperelastic orthotropic model predictions and test results.

A Full-Field Non-Contact Thermal Modal Testing Technique Under Ambient Excitation

Temperature has significant effects on modal parameters of a structure. However, it is difficult to do a full-field dynamic measurement and identify modal parameters of the structure under high temperature and working conditions. In this work, three-dimensional digital image correlation combined with Bayesian operational modal analysis is used to yield a full-field non-contact thermal modal testing technique under ambient excitation. Thermal modal verification experiments are carried out on a titanium plate with free boundary conditions under ambient excitation by a low-cost high-temperature dynamic measurement system. Natural frequencies and mode shapes of the plate under different average high temperatures are studied in detail. From the experimental process, it is believed that the thermal modal testing technique proposed in this work is an effective alternative testing technique to traditional contact testing techniques, and after some improvements, one can achieve thermal modal analysis of a structure under high temperature and working conditions.