3D Digital Image Correlation Research Articles

DIC study of strain concentrations and damage within web-flange junctions of pultruded GFRP bridge decking

This paper reports an experimental study into damage progression within the web-flange junctions of locally-loaded pultruded glass-fibre reinforced-polymer bridge decking, owing to amplified normal and shear stresses at misaligned fibre-resin interfaces. To that end 3D digital image correlation (DIC) is used in three roles, namely quantifying high strains along misaligned fibre layers, detecting onset of damage and identifying macroscopic damage via patterns in the unfiltered strain fields. Both DIC and strain gauges alongside analytical strain predictions are used to increase confidence in the test data. The DIC data reveal that the strains along the misaligned fibre-resin interfaces were shear dominated, and that a 0.8 mm increase of wrinkle-amplitude led to a 92 % increase in peak shear strain. Micro-cracking was detected at approximately 50 % of the test load that caused the first delamination. In repeat tests this load dropped by 27 % due to random transverse cracks within the roving core.

Effects of vegetation on the hydro-mechanical properties of the vadose zone

The hydro-mechanical properties of the vadose zone are strongly influenced by seasonal cycles. The hydraulic behavior of this zone is determined by the coupling of biotic and abiotic factors. The biotic factors are controlled by the physiology and anatomy of the vegetation growing in the area, while the abiotic factors depend on the local soil characteristics, such as water content, void ratio, and matrix structure. In this laboratory-scale investigation, we assess the influence of active biomass, water content, and suction on the particle and pore structure rearrangement. We use x-ray computed tomography and 3D digital image correlation to quantify plant roots at different stages of growth, soil deformation, and water content fluctuations. Our results show that the bulk porosity of vegetated soil is strongly affected by the induced water cycles. The global micro-structure rearrangement due to the double effects of plant water uptake and induced drying-wetting cycles translates into a final bulk porosity increase.

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.

Real-time deformation and stress response of the planar SOFC during sintering

The thermal-mechanical response of the anode-supported planar solid oxide fuel cell (SOFC) during sintering is important for its manufacturing and in-service operation. The integrated micro/nano-indentation and finite element (FE) modeling method was used to characterize the Young’s modulus, yield stress and creeping for the NiO-3YSZ anode and 8YSZ electrolyte at room temperature. Based on the real-time full-field deformation of the half-cell SOFC which was measured using the 3D digital image correlation (DIC), the FE simulation was used to estimate the stress response in a manner of sensitivity study. It shows that the half-cell SOFC warps towards the anode substrate during heating and points in the opposite direction during cooling. The warping deformation of FE simulation matches well with the DIC measurement. In addition, the maximum tensile stress in the electrolyte coat of the half-cell SOFC plate is about 207 MPa if assuming temperature-independence of creeping for the SOFC materials.

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.

3D digital image correlation analysis of medium velocity soft impacts on laminated composite

In aerospace acamedic and industrial world, soft impacts are commonly used to replace bird strike tests for the validation of materials and structures as well as the calibration of numerical models. However in general, the analysis reported show only a few part of the experimental information available. In this paper, three laminate composites made of epoxy resin reinforced by glass or carbon fibres are tested under gelatin impact at several velocities up to complete failure. A detailed analysis based on 3D Digital Image Correlation (3D DIC) and visual inspection of the three laminates is provided for a total of 21 tests with impact velocities in the range 60–112 m/s. DIC extraction provides accurate quantitative displacement fields of the rear face in both time and space. Moreover, specific failure scenarios are identified for each laminate. The results obtained provide a suitable database for the development of numerical models. In addition, all experimental data from DIC extractions are opened to the readers on the Recherche Data Gouv website for comparisons with their own tests or numerical models.

Dual-biprism-based single-camera high-speed 3D-digital image correlation for deformation measurement on sandwich structures under low velocity impact

Abstract Herein, a single-camera stereo digital image correlation (DIC) method is developed for dynamic deformation measurement, and a dual-biprism high-speed stereo camera system is proposed to capture surface images. Then, full-field displacement and strain distributions are obtained after correlation and differential calculation using the stereo-DIC algorithm. After a typical experiment is performed to verify the accuracy of the proposed system, full-field displacement and strain distributions of sandwich panels subjected to low-velocity impacts are determined. These results show that the proposed system is an efficient and convenient tool for dynamic deformation measurement.

Study of elastoplastic deformation and crack evolution mechanism of single-crystal ice during uniaxial compression using 3D digital image correlation

Single-crystal freshwater ice was subjected to uniaxial compression tests with different strain rates and crystal orientations, and the real-time full-field deformation and strain were measured by the three-dimensional digital image correlation (3D DIC) method. The mechanism of elastoplastic deformation and crack evolution of single-crystal ice is discussed based on the basal slip. The maximum compressive strength appeared when the crystal orientation (angle between the C-axis and loading direction) θ=0°/90°. When 45°<θ<90°, an inclined bearing layer appeared and caused the specimen to rotate simultaneously. When 0°<θ⩽45°, the vertical compressive stress was sequentially transmitted through the basal plane, two diagonal expansions to the sidewall appeared. The failure mode and compressive strength of ice exhibited a ductile–brittle transition. The strength was positively correlated with the strain rate below the ductile–brittle transition range. The stress concentration at the crack tip was released through basal slip, inhibiting crack propagation, which showed multi-crack ductile failure. When in the ductile–brittle transition range, the cracks could grow stably, leading to axial splitting failure. When the strain rate was higher, the crack tip could not grow stably, producing inclined cracks and resulting in spalling or axial splitting failure, and the ice exhibited a brittle failure mode.

A compact system for accurate measurement of true stress-strain curves in transparent materials subject to extensive deformation

Accurate quantification of the true stress-strain curve over an extensive strain range is pivotal for elucidating material mechanical properties and simulating non-linear plastic deformation. A novel experimental approach was developed to directly measure true stress-strain behavior in transparent materials. Our setup featured a single 3CCD camera and mirrors, capturing images of both specimen surfaces with bicolored fluorescent speckle patterns. Initially, we determined and corrected the specimen’s refractive index using a point-by-point least squares method. Subsequently, we used multispectral dual 3D digital image correlation (DIC) to reconstruct surface profiles and correct refractive distortions. This allowed precise computation of the deformed cross-sectional area over an expansive strain range. True stress was calculated from the measured engineering stress and computed deformed area. Validity was confirmed by deforming a fluorescent elastomer, and results aligned with the theoretical predictions. This compact experimental setup effectively evaluates true stress-strain relationships in transparent materials under extensive deformation.

Evaluation of Crashworthiness Using High-Speed Imaging, 3D Digital Image Correlation, and Finite Element Analysis

To promote the use of newhigh-strengthmaterials in the automotive industry, the evaluation of crashworthiness is essential, both in terms of finite element (FE) analysis aswell as validation experiments. Thiswork proposes an approach to address the crash performance through high-speed imaging combined with 3D digital image correlation (3D-DIC). By tracking the deformation of the component continuously, cracks can be identified and coupled to the load and intrusion history of the experiment. The so-called crash index (CI) and its decreasing rate (CIDR) can then be estimated using only one single (or a few) component, instead of a set of components with different levels of intrusion and crushing. Crash boxes were axially and dynamically compressed to evaluate the crashworthiness of TRIP-aided bainite ferrite steel and press-hardenable steel. Acalibrated rate-dependent constitutivemodel, and a phenomenological damage model were used to simulate the crash box testing. The absorbed energy, the plastic deformation, and the CIDR were evaluated and compared to the experimentally counterparts. When applying the proposed method to evaluate the CIDR, a good agreement was found when using CI:s reported by other authors using large sets of crash boxes. The FE analyses showed a fairly good agreement with some underestimation in terms of energy absorptions. The crack formation was overestimated resulting in too high a predicted CIDR. It is concluded that the proposed method to evaluate the crashworthiness is promising. To improve the modelling accuracy, better prediction of the crack formation is needed and the introduction of the intrinsic material property, fracture toughness, is suggested for future investigations and model improvements.

Inverse identification of in-situ curing shrinkage using a method combining 3D digital image correlation and finite-element simulation

Curing shrinkage of adhesives in the bonding process usually leads to deformation and residual stresses. The measurement of curing shrinkage is valuable in providing fundamental information for better understanding, controlling, and optimizing the curing process. This paper developed an efficient hybrid inverse identification method for in-situ measurement of the volume shrinkage. This method associates the artificial fish swarm algorithm (AFSA) with a finite element method (FEM) and 3D digital image correlation (3D-DIC) technology. A homemade apparatus for experimental characterization of curing shrinkage is prepared and tested. The evolution of the volume shrinkage is inversely identified by matching the 3D-DIC and the FEM results using the AFSA algorithm. The results are further validated by a direct-density measurement and the standard physical property of the adhesive. Those experimental results demonstrated that the proposed method is a viable non-contact, non-destructive, and in-situ technique that can be applied to measure the in-situ curing shrinkage.

Structural response of monolithic and multi-stacked AA2014-T6 sheet specimens subjected to shock loading

Experimental and numerical investigations of the shock response of AA2014-T6 sheets are presented in the current study. A double-stage shock loading apparatus is utilized for loading the simply supported specimens under the shock loading. The experiments are performed on two different sheet thicknesses i.e., 1 mm and 2 mm. The spatial out-of-plane displacement of the specimens is obtained using 3D digital image correlation (DIC) technique. ABAQUS/Explicit is utilized for finite element (FE) modelling and simulating the shock loading event. A modified loading function is incorporated in the FE model to approximate the change in the specimen loading area and shock loading magnitude for the deformable specimens. The experimentally and numerically obtained out-of-plane displacement of the specimens are compared and agreement between both is quantified using Russell error technique. A series of experiments are conducted to investigate the effect of change in shock loading magnitude on the deformation phenomenon and corresponding energy dissipation. Alloy sheet of 2 mm thickness is observed to be better shock resistant than 1 mm sheet as the plastic dissipation energy per unit mass is higher for 2 mm thick sheet. Additionally, the shock behaviour of layered targets is also investigated for effective thicknesses of 2 mm and 3 mm. The performance of monolithic sheet of 2 mm is observed to be better than layered configuration of (1 + 1) mm. For the effective thickness of 3 mm, the order of decreasing shock performance is observed as (2 + 1) mm, (1 + 2) mm, and (1 + 1 + 1) mm.

Full-field dynamic response of low-velocity impact on an elastic plate using 3D digital image correlation

Measurement of the impact process is challenging due to its short duration and high frequency response. Due to the very small strain in low-velocity impacts, the requirements for the temporal and spatial resolution of test methods are extremely high. Traditionally, strain gauges or lasers are commonly used to measure the dynamic response of a single point, or quasi-static loading is used to achieve full-field response. To finely describe the transient full-field deformation process of low-velocity impacts, a high-speed imaging system combined with 3D digital image correlation (DIC) technique is set up to investigate the instantaneous responses of impact on a polyvinyl chloride (PVC) plate at the ms and με level. The full-field deformation of the contact surface and the whole process of elastic wave propagation are measured. The measurement by DIC closely matches the measurement by strain gauges and agrees well with the numerical simulation results. The measurement reveals that the “multi-micro-impacts” phenomenon may happen during a complete impact process due to the complex strain wave propagation. This work provides a benchmark case for low-velocity impact full-field testing, and the results show that 3D DIC can accurately evaluate dynamic behaviors of low-velocity impact between flexible bodies and can accurately describe the spatiotemporal propagation characteristics of strain waves.

Evolution of capillary pressure in 3D-printed concrete elements: numerical modelling and experimental validation

In the initial hours following extrusion, 3D-printed concrete elements undergo intensive water evaporation. This process leads to significant negative capillary pressure within the system. During the period before solidification, this capillary pressure induces volumetric contractions, commonly referred to as plastic shrinkage, in the 3D-printed concrete, and as a result, causes cracking. Therefore, managing and forecasting the negative capillary pressure in freshly deposited concrete filaments is crucial to mitigating the effects of plastic shrinkage. In this study, the progression of capillary pressure in 3D-printed elements, with filament thickness ranging from 37.5 mm to 150.0 mm, was experimentally evaluated and numerically simulated. The numerical simulations utilised the extended Richard's equation. Shrinkage strains were empirically measured using 3D digital image correlation and compared with numerical outcomes. Additionally, we examined various combinations of parameters to analyse their influence on the accuracy of the numerical results.

Experimental and Numerical Study of Healing Effect on Delamination Defect in Infusible Thermoplastic Composite Laminates.

The integrity of delaminated composite structures can be restored by introducing a thermally-based healing effect on continuous fiber-reinforced thermoplastic composites (CFRTPC). The phenomenon of thermoplastics retaining their properties after melting and consolidation has been applied by heating the delaminated composite plates above their glass transition temperature under pressure. In the current investigation, the composite is comprised of Methyl methacrylate (MMA)-based infusible lamination resin combined with benzoyl peroxide initiator, which polymerizes into a Polymethyl methacrylate (PMMA) matrix. For the reinforcement, unidirectional 220 gr/m2 glass filament fabric was used. Delamination damage is artificially induced during the fabrication of laminate plates. The distributed delamination region before and after thermally activated healing was determined by using non-destructive testing with active thermography. An experimental approach is employed to characterize the thermal healing effect on mechanical properties. Experimentally determined technological parameters for thermal healing have been successfully applied to repair delamination defects on composite plates. Based on the compression-after-impact (CAI) test methodology, the intact, damaged, and healed composite laminates were loaded cyclically to evaluate the healing effect on stiffness and strength. During the CAI test, the 3D digital image correlation (DIC) technique was used to measure the displacement and deformation fields. Experimental results reveal the difference between the behavior of healed and damaged specimens. Additionally, the numerical models of intact, damaged, and healed composite laminates were developed using the finite element code LS-Dyna. Numerical models with calibrated material properties and tie-break contact constants provide good correlation with experimental results and allow for the prediction of the mechanical behavior of intact, damaged, and healed laminated plates. The comparison analysis based on CAI test results and modal characteristics obtained by the 3D Laser Doppler Vibrometer (Polytec GmbH, Karlsbad, Germany) proved that thermal healing partially restores the mechanical properties of damaged laminate plates. In contrast, active thermography does not necessarily indicate a healing effect.

Performance of 3D-Printed Beams and Slabs Using Self-Sensing Cementitious Composites and DIC Method.

This paper aims to explore the structural performance of 3D-printed and casted cement-based steel-reinforced concrete beams and one-way slabs incorporating short carbon fibre and activated carbon powder, which have been shown to enhance concrete's flexural strength and reduce its electrical resistivity. The samples are cast and printed in 250 × 325 × 3500 mm beams and 150 × 400 × 3500 mm one-way slabs and mechanical, electrical, and piezoresistivity properties were measured. This length of beams and one-way slabs with rebars have been considered as they can magnify the flexural and cracking behaviour and make them easier to be monitored and analysed. The samples were loaded up to 80% of maximum stress. Crack propagation and strain was assessed using the 2D digital image correlation (DIC) method. The results compared samples under continuously increasing loads between 3D-printed and cast samples. The 3D-printed composites had a better piezoresistive response due to the enhanced anisotropic behaviour. DIC analysis illustrated similar results among different samples, while 3D-printed blocks had lower cracking performance due to the horizontal case fracture in lower stress.

Dynamic instability of reinforced hollow cylinders in a confined underwater environment

An experimental investigation was conducted to understand the collapse mechanisms of internally ring stiffened aluminum cylinders under uniform hydrostatic loading in a confined underwater environment. The implosion of ring stiffened cylinders was studied using a combination of high-speed photography and 3D Digital Image Correlation (DIC). The results show that as stiffener thickness is decreased, the collapse of the structure transitions from two segments collapsing in mode III with the stiffener serving as boundary separating the segments to one uniform mode II collapse where the ring stiffener collapses with the structure. Furthermore, in the cases with two collapses, the behavior of the structure can be described as approaching that of two cylinders divided by a simply-supported boundary condition at the location of the stiffener. The ring thickness also affects the collapse pressure of the cylinder, radial velocity during collapse at the location of the ring stiffener, and dwell time between the collapse of two sections in cases with two collapses.

Experimental and numerical investigation of the intra-ply shear behaviour of unidirectional prepreg forming through picture-frame test

Intra-ply shear behaviour of uncured composite plies strongly influences component quality in advanced manufacturing processes such as prepreg compression moulding (PCM) and double diaphragm forming (DDF). This study investigates a straightforward method to characterise the intra-ply shear behaviour of a carbon fibre/epoxy UD prepreg using a specially designed picture-frame rig, by which specimens can be tested without involving inter-ply shear as would normally be observed in cross-plied UD prepreg stacks. Applying the proposed method, it is seen that specimens tend to suffer transverse buckling/wrinkling and local fibre-splitting at large shear strains. 3D digital image correlation (DIC) and a non-contacting video extensometer were utilised to determine the shear strain distribution throughout the test and particularly to determine the onset of out-of-plane deformations such that the trellis shear deformation portion of the test can be identified. The obtained shear stress-strain results show a temperature- and rate-dependent viscoelastic response, with the greatest influence from the temperature. The obtained in-plane shear properties were applied in the numerical simulation of the picture frame test based on a hypoelastic law. Although the predicted reaction forces are greater than experimental results at high strains due several factors including local fibre-splitting, a good agreement overall between physical test data and simulation results is seen for all test conditions. Finally, it is demonstrated that major advantages of the proposed test with respect to the conventional picture-frame test are that only load-extension data are required from the trellis shear experiment to calculate accurately the intra-ply shear stress-strain relationship and that the deformation rate can be easily controlled.

Coupled strain and temperature gradient analysis in curved surfaces

AbstractA common method in experimental mechanics is 3D digital image correlation (DIC) for determining deformations of curved surfaces, whereby the motion of material points is measured. The temperatures induced by the deformation of surfaces or by other heat sources are of particular interest as well. In this context, surface temperatures can be measured using infrared thermography systems. However, the disadvantage of this approach is that a thermographic camera only provides the two‐dimensional temperature distribution (plane images) of three‐dimensionally curved surfaces. Thus, the temperature and temperature gradients on the curved surface assigned to material points cannot be specified. However, for particular problems the temperature and the motion of material points are of particular interest. In the literature, planar problems are studied and simplifying assumptions are made so that a simple coupling of thermography and DIC is possible. In contrast, this contribution presents a method where 3D DIC is coupled with thermography in such a way that the temperature, temperature gradient, as well as displacement and strain distributions at material points of curved surfaces can be determined over temporal processes. The method also allows a continuous strain and temperature gradient determination over the entire domain, since a special class of functions named radial basis functions is used for interpolating the measured data.

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.