Combination Of Digital Image Correlation Research Articles

Interferometric-scale full-field vibration measurement by a combination of digital image correlation and laser vibrometer

Digital Image Correlation (DIC) is a crucial noncontact full-field optical measurement method used in various fields. However, in practical applications, DIC is affected by systematic and random noises, leading to experimental resolutions lower than theoretical ones. In this study, we proposed a laser Doppler vibrometer guided DIC to perform vibration measurements. 3D-DIC obtains a sequence of out of displacement field initially. A three-dimensional frequency domain collaborative filtering (3D-FDCF) method that utilizes Laser Doppler vibrometer (LDV) single-point data to assist in processing of the displacement field sequence pixel-wise is adopted. The 3D-FDCF method combines lowpass filtering in the spatial frequency domain with LDV-guided bandpass filtering in the temporal frequency domain. The effectiveness of the 3D-FDCF method is demonstrated through a comparison among DIC data, the filtered DIC data, and continuously scanning LDV data. The experiment results demonstrate the 3D-FDCF method's capability in measuring vibration amplitudes of several hundred nanometers with the size of a test sample of about 100 mm × 100 mm, supporting the statement of interferometric scale full-field vibration measurement by DIC with the guidance of the LDV data.

Tension and Shear Behaviour of Basalt Fiber Bio-Composites with Digital Image Correlation and Acoustic Emission Monitoring.

This research investigates the mechanical behavior and damage evolution in cross-ply basalt fiber composites subjected to different loading modes. A modified Arcan rig for simultaneous acoustic emission (AE) monitoring was designed and manufactured to apply quasi-isotropic shear, combined tensile and shear loading, and pure tensile loading on specimens with a central notch. Digital image correlation (DIC) was applied for high-resolution strain measurements. The measured failure strengths of the bio-composite specimens under different loading angles are presented. The different competing failure mechanisms that contribute to the local reduction in stress concentration are described. Different damage mechanisms trigger elastic waves in the composite, with distinct AE signatures that closely follow the sequence of fracture mechanisms. AE monitoring is employed to capture signals associated with structural damage initiation and progression. The characteristic parameters of AE signals are correlated with crack modes and damage mechanisms. The evolution of AE parameters during the peak load transition is presented, which enables the timely AE detection of the maximum load transition. The combination of DIC and AE monitoring improves understanding of the mechanical response and failure mechanisms in cross-ply basalt fiber composites, offering valuable insights for possible performance monitoring and structural reliability in diverse engineering applications.

Evaluation of Damage Stress Thresholds and Mechanical Properties of Granite: New Insights from Digital Image Correlation and GB-FDEM

We employed a novel combination of digital image correlation (DIC) and grain-based hybrid finite–discrete element method (GB-FDEM) to improve the comprehension of the relationships between microstructural features and the mechanical properties of granitic rocks. DIC and numerical results showed that macrocracks initiated and propagated along grain boundaries among different minerals driven by the high stiffness contrast between the compliant biotite and the stiffer feldspar/quartz grains. Surface deformation analyses revealed that tensile-dominated macrocracks open at monotonically increased rates before the crack damage threshold, and the opening accelerated afterwards with the increased shear component. The onset of the acceleration of the opening rate of macrocracks can be used to infer the crack damage threshold. Both strain and acoustic emission were used to infer damage stress thresholds in the synthetic numerical samples. Numerical results showed that the damage stress thresholds and uniaxial compressive strength decrease with increasing grain size following log-linear relations. Coarse-grained samples tend to fail by axial splitting, while fine-grained samples fail by shear zone formation. Biotite and quartz contents significantly affect mechanical properties, while quartz to feldspar ratio is positively related to the mechanical properties. Our study demonstrates the capacities of DIC and GB-FDEM in inferring damage conditions in granitic rocks and clarifies the microstructural control of the macroscopic mechanical behaviors. Our results also provide a comprehensive understanding of the systematics of strain localization, crack development, and acoustic emission during the rock progressive failure process.

Unveiling fracture mechanics of a curved coating/substrate system by combined digital image correlation and numerical finite element analyses

A mechanism of coated, curved substrate failure is characterized via a C-ring compression test and multiscale modeling analysis. Coating crack formation is driven by sudden through-thickness cleavage in accordance with Mode I fracture type. The fracture is arrested at the coating/substrate interface. The cracks continue to widen as the underlying substrate experiences periodic regions of high stress under the crack and regions of relaxed stresses under the remaining intact coating. An analytical, closed form solution model developed via curved beam theory captures the hoop stress in the axis transverse to external loading and predicts the external load at crack initiation. After the onset of cracking, the system transitions to cleavage driven failure, which is simulated via element deletion failure in a small-scale explicit dynamics finite element model. The macroscale explicit dynamics finite element model, analytical solution, and bulk experimental results agree. The correlation between coating microstructure and deposition method is also investigated and reveals that high interfacial roughness and equiaxed grain morphology correspond to higher loader carrying capability and lower crack density while low interfacial roughness and smooth columnar grains correspond to higher strain to coating failure.

A complete characterization of THE fracture forming limits in bulk forming by means of an upset geometry sequence

This paper presents an upset geometry sequence to determine the fracture forming limits in a wide variety of strain loading paths ranging from uniaxial compression to equibiaxial tension. The strains at fracture in principal strain space are obtained by combination of digital image correlation and experimental evolutions of the compression force versus time, and their representation in the effective strain versus stress triaxiality space is accomplished by means of a new analytical framework that uses the instantaneous slope of the strain loading paths. Modeling of the experimental strains at fracture by means of an uncoupled ductile fracture criterion built upon combination of the Cockcroft-Latham and McClintock criteria and fractography analysis using a scanning electron microscope allow understanding and characterizing the crack opening modes by shear and tension as well as the uncertainty region inside which mixed crack opening modes are observed. Results confirm that the overall philosophy and objectives underlying the new upset geometry sequence for determining the fracture forming limits in bulk forming resemble those of the Nakajima test that is commonly used in sheet forming.

Combining Digital Image Correlation and Acoustic Emission to Characterize the Flexural Behavior of Flax Biocomposites

Understanding the effect of staking sequences and identifying the damage occurring within a structure using a structural health monitoring system are the keys to an efficient design of composite-based parts. In this research, a combination of digital image correlation (DIC) and acoustic emission (AE) is used to locate and classify the type of damage depending on the stacking sequence of the laminate during flexural loading. As a first step, the results of the strain fields for unidirectional, cross-ply, and quasi-isotropic laminates were compared to discuss their global behavior and to correlate the different damage patterns with the possible failure mechanisms. The damage was then addressed using a comprehensive interpretation of the acoustic emission signatures and the K-means classification of the acoustic events. The development of each damage mechanism was correlated to the applied load and expressed as a function of the loading rate to highlight the effect of the stacking sequence. Finally, the results of DIC and AE were combined to improve the reliability of the damage investigation without limiting the failure mechanism to matrix cracking, interfacial failure, and fiber breakage, as expected by the unsupervised event clustering.

Combination of Digital Image Correlation (DIC) and in situ 3D-μ-CT in the analysis of the relationship between strains and porosity under creep loading

Abstract In situ 3D μ-XCT allows the time and space resolved measurement and analysis of material damage in the component volume, whereas the Digital Image Correlation (DIC) is a 2D method for the analysis of deformation measured on the surfaces of components. In situ 3D μ-XCT measurements were performed on cylindrical specimen made of SiC particle reinforced titanium MMC (MMC: Metal Matrix Composite) (15 % SiC particles) during creep load. The formation and evolution of voids were subsequently analyzed. Due to the rotationally symmetric sample geometry, the analysis of the deformation in the interior of the material by DIC using 2D slices is possible and evident. The dot pattern required to calculate the strain using DIC (speckle pattern) is provided by the intrinsic particle reinforcement of the MMCs. Temporally and locally changing and time-variant strain fields in both the tensile as well as the compressive range could be detected correlating with void formation and development area.

High-Accuracy Three-Dimensional Deformation Measurement System Based on Fringe Projection and Speckle Correlation.

Fringe projection profilometry (FPP) and digital image correlation (DIC) are widely applied in three-dimensional (3D) measurements. The combination of DIC and FPP can effectively overcome their respective shortcomings. However, the speckle on the surface of an object seriously affects the quality and modulation of fringe images captured by cameras, which will lead to non-negligible errors in the measurement results. In this paper, we propose a fringe image extraction method based on deep learning technology, which transforms speckle-embedded fringe images into speckle-free fringe images. The principle of the proposed method, 3D coordinate calculation, and deformation measurements are introduced. Compared with the traditional 3D-DIC method, the experimental results show that this method is effective and precise.

An upset geometry sequence for determining the formability limits in bulk forming

This paper presents an upset geometry sequence capable of providing strain loading paths from uniaxial compression to biaxial stretching. Combination of digital image correlation and experimental force vs. time evolutions allows determining the fracture strains and the instantaneous slope of the strain loading paths at the instant of cracking in principal strain space. Fractography using scanning electron microscopy helps identifying the crack opening modes corresponding to the different fracture strains. Results show that the proposed upset geometry sequence allows creating a new testing methodology for bulk forming similar to that of sheet forming with the widely used Nakajima test.

Microstructural origin of anisotropic tensile ductility of Al-Si alloy manufactured by laser powder bed fusion

Aluminum alloys fabricated by laser powder bed fusion (L-PBF) exhibit anisotropic tensile ductility. To identify microstructural origins in melt-pool (MP) structures (formed by the l-PBF process) contributing to the anisotropic ductility, the local strain distribution inside the MP structure in deformation was quantified by a combination of digital image correlation (DIC) strain analysis and in-situ SEM observations of tensile tests. It was found that higher strain was localized in locally coarsened microstructures (softer regions) along melt-pool boundaries (MPBs). The strain localization played a significant role in crack initiation (and propagation) around MPBs, contributing to fracture. The strain localization at MPBs changed depending on the geometrical relation of the MPBs with the loading direction (LD), which was controlled by the LD with respect to the building direction of l-PBF samples. The three-dimensional MPB distribution related to the LD would be responsible for the anisotropic ductility.

Large‐scale experiments on concrete hinges under general loading

AbstractThe structural behavior of concrete hinges under general loading is far from being properly understood, which is to a large extent due to the lack of pertinent experimental data. This paper contributes to filling this knowledge gap by presenting and discussing the results of an experimental campaign on one‐way Freyssinet concrete hinges. Seven large‐scale concrete hinges were tested in the Large Universal Shell Element Tester, which allowed the investigation of their behavior under general loading by all six stress resultants. A combination of digital image correlation and distributed fiber optic measurements allowed a deeper insight into the structural behavior of the specimens. The tested hinges could sustain very high axial stresses exceeding 4.5 times the uniaxial concrete compressive strength, large rotations of over 60 mrad, and shear stresses in transverse and longitudinal directions up to 2.24 times the axial compressive stress. The resistance to bending moments about the strong axis and torques also proved to be significant. A moderate amount of reinforcement crossing the hinge throat considerably increased the shear resistance at low axial stresses and produced a ductile shear behavior.

Damage source and its evolution of ultra-high performance concrete monitoring by digital image correlation and acoustic emission technologies

Ultra-high performance concrete (UHPC) is a kind of fiber-reinforced cement-based materials with outstanding mechanical properties and much enhanced toughness. In this paper, digital image correlation (DIC) and acoustic emission (AE) techniques are used to study the damage mode of UHPC during loading process. The results demonstrate that the combination of DIC and AE can identify the internal damage sources and also detect the surface cracks in UHPC. With the addition of steel fibers, the strain of cracking point of UHPC exposed to steam curing is 1.61 times greater than that exposed to standard curing. Furthermore, the b-value analysis provides the critical value for UHPC damage, and the reference values for the warning threshold and warning time are proposed. Using RA-AF correlation analysis, UHPC displays a mixed damage with tensile damage predominating. By analyzing the intensity of the AE signal, the safety of UHPC (20% silica fume and 1% steel fibers) exposed to steam curing is 17 times higher than ordinary reinforced concrete beams. Moreover, the damage mode of UHPC is multi-point damage, which significantly increases the ultimate bending load and bending toughness of the UHPC, and improves bending resistance.

Combining digital image correlation and phased-array ultrasonics for non-destructive testing of translaminar fracture in composite laminates

A simple and efficient non-destructive testing method is presented to quantify translaminar fracture properties in quasi-isotropic [90/45/0/-45]3s T800SC/3900-2B carbon fibre-reinforced polymer laminates subjected to Over-height Compact Tension (OCT) and Compact Compression (CC) fracture tests. The combination of Digital Image Correlation (DIC) with phased-array ultrasonics enables the consistent measurement of the fibre-dominant translaminar crack length, damage height and hence damage resistance curves as well as the continuous monitoring of the Fracture Process Zone (FPZ). The length of the FPZ is determined by overlaying regions of saturated (fully developed) fibre damage obtained from DIC and ultrasonic C-scans. The analysis of the progressive fracture tests reveals average laminate fracture energies of 161 kJ/m2 and 68 kJ/m2 and FPZ lengths of up to 8–12 mm and 10 mm in tension and compression, respectively. It is shown that the proposed method works best when fibre-dominated damage is confined to a narrow band normal to the loading direction as observed in CC tests. In contrast, OCT test results show that delamination and the corresponding isolated ply behaviour can alter the DIC analyses and hence complicate the measurement of translaminar fracture properties.

In-situ study of microstructural evolution and strain distribution during single axis tension of 316L stainless steel prepared by selective laser melting

A combined digital image correlation (DIC) and electron backscatter diffraction (EBSD) study of the multi-scale strain distribution and microstructure evolution during tensile loading has been carried on 316L stainless steel samples prepared by selective laser melting (SLM). The initial material shows a range of microstructural heterogeneity. Macro- and micro-DIC results reveal a non-uniform distribution of plastic strain over several length scales, including the formation of localized slip-bands at the intra-grain level. No obvious correlation is found between the heterogeneity in plastic strain and either grain size, grain morphology or the orientation of the cellular structures formed during SLM. Intragranular orientation subdivision and the evolution of local misorientation have also been investigated by EBSD during tension, where a complex pattern of heterogeneity in both microstructure and plastic strain is found.

3D printed hierarchical re-entrant honeycombs: Enhanced mechanical properties and the underlying deformation mechanisms

Re-entrant honeycombs are one type of lightweight cellular materials with superior energy absorption and impact resistance. Yet, the mechanical properties of re-entrant honeycombs need to be further improved due to its bending-dominated deformation mechanism. In this study, we designed a novel stretching-dominated re-entrant honeycomb by combining the structural hierarchy and auxetic cellular configurations. Such hierarchical re-entrant honeycomb (H-ReH) is manufactured through fine-resolution 3D printing technique. The mechanical behavior and deformation mechanism of the designed H-ReH has been investigated through combined digital image correlation and finite element simulation. The 3D-printed H-ReHs exhibit enhanced specific stiffness, specific initial-buckling strength, structural stability and specific energy absorption capacity due to the uniquely combined deformation mechanisms. A competition between the 1st order and the 2nd order hierarchy has been revealed, which governs the mechanical properties of the H-ReHs. These findings provide thorough understandings and facilitate future design of lightweight but robust cellular materials.

The localization of plastic deformation in the precipitate free zone of an Al-Mg-Si-Mn alloy

Precipitate free zones (PFZ) near grain boundaries of aluminum alloys are known to have important effects on the localization of plastic deformation in these regions. The objective of the current study was to quantify strain localization in the PFZ using a combination of digital image correlation (DIC) and crystal plasticity simulations for an Al-Mg-Si-Mn alloy. Two different cooling paths after solution treatment were considered: (i) water quenched and (ii) air cooled followed in both cases by artificially aged to the peak strength. The samples were deformed in tension with strain increments of ∼ 0.01 to strains of 0.01-0.05 with the local strain calculated from the displacement field measured by DIC. It was found that the level of strain localization depends on (i) the PFZ thickness and (ii) the orientation of the trace of the grain boundary to the loading axis. Further, the state of strain was characterized in terms of the level of shear parallel to and stretch perpendicular to the grain boundary. Experiments and simulations demonstrated that localization of plastic strain in the PFZ was favoured for (i) thicker PFZ's and (ii) grain boundaries inclined at angles of 15–75o with respect to the loading axis. The state of strain in the PFZ was dominated by shear parallel to the grain boundary for grain boundaries inclined to the loading axis.

Characterization and Finite Element Modeling for Thermoset Resin of Carbon Fiber Prepregs During Curing

Abstract In this study, an epoxy resin, YZ-05, designed specifically for carbon fiber reinforced polymer prepregs, was characterized and modeled. A degassing method for the highly viscous YZ-05 was established for specimen preparation. To numerically model the behavior of YZ-05 in curing, several components, including the heat transfer, curing kinetics, and viscoelastic constitutive law ones, were developed, and the corresponding material properties to be input were tested. As YZ-05 shows severe creep at high temperature under mechanical loading, the combination of digital image correlation (DIC) and thermography technique was utilized to obtain its thermal expansion and chemical shrinkage. In the aspects of viscoelastic behavior, stress relaxation tests were performed based on time–temperature superposition principle with a numerical method to calculate shift factors. After development and input identification, these modeling components for YZ-05 resin were integrated and the modeling results were validated using experiments, where bending of resin beams was induced during curing.

Effect of Layer Thickness on the Physical and Mechanical Properties of Sand Powder 3D Printing Specimens

The application of sand powder three-dimensional (3D) printing technology in the field of rock mechanics and mining engineering has tremendous potential, but it is still in the preliminary exploration stage. This study investigated the effect of printing layer thickness on the physical and mechanical properties of rock-like specimens with sand powder 3D printing. Quartz sand powder was used as the printing material, and the specimens were prepared with three different layer thicknesses of 0.2, 0.3, and 0.4 mm. Uniaxial compression tests with a combination of digital image correlation (DIC), acoustic emission (AE) and 3D microscope observations were performed to analyze the mechanical properties and failure patterns of the specimens during loading. Experimental findings showed that increasing the layer thickness from 0.2 to 0.4 mm would result in a decrease in the weight, density, uniaxial compression strength, and elastic modulus of the specimens. The stress-strain curve, deformation and failure patterns, crack growth process, and AE characteristics of the specimens with a layer thickness of 0.2 mm are similar to the AE characteristics of rock-like material, whereas the specimens with layer thicknesses of 0.3 and 0.4 mm deform like a ductile material, which is not appropriate for simulation of coal or rock mass. In future studies, rock-like specimens should be prepared with a small layer thickness.

Crystallography and deformation behavior of α phase precipitate at twin/matrix interface in a cold rolled metastable Ti-12Mo alloy

A layered α/β Ti alloy was developed by cold rolling and subsequent aging heat treatment of a metastable β Ti-12Mo alloy. The microstructure consisted of coarse equiaxed β grains containing a large number of deformation twins. After aging, α phase was found to preferentially precipitate at twin boundaries following a fixed crystallographic orientation relationship with respect to both the twin and the matrix. Finely dispersed α precipitate were also observed in the matrix and inside some thick twins and were inferred to be due to the presence of parallel nano-sized α” martensite inside thick twins and ω phase formed during cold rolling. The deformation behavior of aged sample was finally characterized by a combination of digital image correlation (DIC) and electron backscatter diffraction (EBSD) analyses. An increase in yield strength was noted when compared with the solution treated sample. It was found that plastic deformation was highly heterogeneous and mostly located in the α layer at the interface between the matrix and thick twins. This heterogeneity was finally discussed based on an elastic stiffness analysis and the specific crystallographic configuration at this interface.

The Localization of Plastic Deformation in the Precipitate Free Zone of an Al-Mg-Si-Mn Alloy

Precipitate free zones (PFZ) near grain boundaries are known to have important effects on the fracture of aluminum alloys. It has been shown qualitatively that deformation localized in the PFZ leads to the acceleration of damage initiation, growth and coalescence in this region, i.e. intergranular fracture. The objective of the current study was to quantify strain localization in the PFZ using a combination of digital image correlation (DIC) and crystal plasticity simulations for an Al-Mg-Si-Mn alloy. Two different cooling paths after solution treatment were considered: i) water quenched and ii) air cooled followed in both cases by artificially aged to the peak strength. The samples were deformed in tension with strain increments of ≈ 0.01 to strains of 0.01-0.05 with the local strain calculated from the displacement field measured by DIC. It was found that the level of strain localization depends on i) the PFZ thickness and ii) the orientation of the trace of the grain boundary to the loading axis. Further, the state of strain was characterized in terms of the level of shear parallel to and stretch perpendicular to the grain boundary. Experiments and simulations demonstrated that localization of plastic strain in the PFZ was favoured for i) thicker PFZ’s and ii) grain boundaries inclined at angles of 15-75 o with respect to the loading axis. The state of strain in the PFZ was dominated by shear parallel to the grain boundary for grain boundaries inclined to the loading axis.