3D Digital Image Correlation Research Articles

A Method for Dynamic Kolsky Bar Compression at High Temperatures: Application to Ti-6Al-4V

Abstract An experimental apparatus for measuring the dynamic behavior of materials subjected to strain rates on the order of 10 $$^3$$ 3 s $$^{-1}$$ - 1 and temperatures up to 800°C with a unique triple actuation system is developed in this work. This system is based on the traditional Kolsky (or split-Hopkinson pressure) bar design, with the addition of an external furnace used to heat the specimen to the desired temperature. A synchronized triple pneumatic actuation system is used to control the motion and timing of the the sample, incident, and transmitted bars. The cold contact time (CCT), or the time during which the heated sample is in contact with the room temperature bars before compression, is measured experimentally and carefully controlled to minimize the development of a temperature gradient across the sample and avoid heating of the bars. Experiments are performed in conjunction with ultra high speed imaging and 2D digital image correlation (DIC), as well as high speed thermal imaging. To verify the viability of the proposed system, experiments were conducted on Ti-6Al-4V (wt.%) at temperatures from 25°C up to and 800°C at an average strain rate of approximately 1200 s $$^{-1}$$ - 1 .

Combination of in-/and ex-situ damage detection methods to investigate the forming behavior of fiber-metal-laminates

In this study, the forming behavior of fiber-metal laminates (FML) is investigated by a combination of different (in- and ex-situ) measurement techniques. Using FML-samples consisting of aluminum and carbon fiber reinforced polyamide-6, deep-drawing tests were employed at high temperatures. It can be concluded a conventional approach based on the forming limit curve (FLC) is not suitable to predict the failure initiated in the multi-material setup as principal strains cannot differentiate the strain in aluminum and CFRP and lack sensitivity to detect other relevant failure modes, such as debonding as well as debonding in between layers. To better understand the failure behavior due to forming of FML, an experimental setup, that based on the Nakajima-test, was developed, using in-situ acoustic emission testing, 3D digital image correlation as well as ex-situ X-ray computed tomography. The combined results from all methods helped to gain a deeper insight into how thermoplastic FML behave during deep drawing at elevated temperatures especially focusing on evolving damage inside the hybrid material

Puck 3D-based modeling and validation of progressive failure in instrumented glass fiber-reinforced polypropylene via the split-disk test

This study analyzes the mechanical behavior and damage progression of filament-wound thermoplastic composite rings, focusing on the effects of embedded fiber optic (FO) sensors. Utilizing a split-disk test, the study evaluates both experimental and numerical approaches to examine the impact of FO sensors in glass fiber-reinforced polypropylene composite rings. The split-disk test is employed to measure key mechanical properties such as hoop tensile strength, stiffness and failure strain using strain gauges and 3D Digital Image Correlation (DIC). The research specifically examines two extreme configurations of FO sensor placement: parallel and perpendicular to the reinforced fibers. The objective is to propose sensor integration that minimizes potential negative effects on the material's properties. Both instrumented and non-instrumented samples are analyzed numerically and experimentally. The experimental phase involves detailed mechanical characterization using the split-disk test, while the numerical approach uses a developed UMAT finite element model based on the 3D Puck failure criterion and an element weakening method for progressive failure analysis. The numerical models adopt real microstructural details according to optical microscopic analysis. The study concludes that parallel embedded FO sensors are preferable as they enhance the ultimate strength to failure and avoid creating resin-rich zones near the sensor, thereby improving the overall mechanical performance of the composite rings. The 3D Puck failure criterion combined with the element weakening method provides accurate predictions of fiber failure initiation and growth in the composite rings.

EXPERIMENTAL ANALYSIS OF POISSON RATIO ON METAMATERIALS MANUFACTURED FROM CRUMPLED ALUMINUM FOIL SUBJECTED TO UNIAXIAL COMPRESSION

In this work experimental results are presented concerning the auxetic behavior of a crumpled metamaterial manufactured with aluminum foil, so far such experimental evidence has not been reported by other authors. Thus, 2D digital image correlation (DIC) was used to make full field measurements of longitudinal and transverse strains on the surface of crumpled aluminum specimens under axial compression; it was no possible to use conventional methods on the measurements of strains, such as strain gages or extensometers, due to the irregular topography on the surface of the specimens. The obtained results exhibit the auxetic nature of the aluminum crumpled material, with Poisson´s ratio values that vary from ?=-0.17 to ?=-0.02 for relative densities in the range ?_r=0.07 to ?_r=0.21. Keywords: Auxetic, Digital Image Correlation, Crumpled material, Poisson, Computer vision system.

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

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

Temperature and rate dependent shear characterization and modeling of spread-tow woven Flax/PP composite laminates

This paper investigates the in-plane shear behavior of spread-tow woven structured flax fiber-reinforced polypropylene composites, focusing on temperature and displacement rate effects. For this aim, the study includes bias-extension experiments to characterize the shear behavior of the material. Several experiments were conducted at different displacement rates and temperature levels. The temperature levels were chosen to encompass the material's behavior during solid and molten-state thermoforming, given the melting and decomposition temperatures acquired from differential scanning calorimetry and thermogravimetric analysis tests, respectively. A new fixture was designed and manufactured to allow pre-heating of the oven and rapid placement of the samples, which in turn, prevents their degradation for the time duration required to reach a uniform temperature distribution in the oven. During the experiments, the 3D digital image correlation technique accurately measured local deformations and strains on the specimen's surface under varying conditions. Further, a finite element model is developed, incorporating a fiber reorientation algorithm with a hypo-elastic shear model to simulate the material's temperature and rate-dependent behavior. The finite element shear angle distributions, as well as the shear angle-force and shear angle-displacement curves, are compared with the Digital Image Correlation (DIC) data and load measurements for different test conditions, showing good agreement between the numerical and experimental approaches.

High-Speed Three-Dimensional-Digital Image Correlation and Schlieren Imaging Integrated With Shock Tube Loading for Investigating Dynamic Response of Human Tympanic Membrane Exposed to Blasts.

Investigating the dynamic response of human tympanic membranes (TMs) exposed to blasts requires full-field-of-view and three-dimensional (3D) methodologies. Our paper introduces a system that combines high-speed 3D digital image correlation (HS 3D-DIC) and Schlieren imaging (HS-SI) with a custom-designed shock tube for generating blast waves. This integrated system allows us to measure TM surface motions under intense transient loading, capturing full-field-of-view shape deformations exceeding 100 μm with a temporal resolution of 10 μs. System characterization encompasses (i) measuring the shock tube's output levels and repeatability, (ii) assessment of the spatial and temporal resolutions of the imaging techniques, and (iii) identification of overall system limitations. Optimizing these factors is crucial for improving the reliability of our system to ensure the accurate measurement of deformations. To assess our shock tube's reliability in generating repeated blast waves, we instrumented it with high-pressure (HP) and high-frequency (HF) pressure sensors along the blast wave pathway to record overpressure waveforms and compared them with Schlieren imaging visualized blast waves. We validate our HS 3D-DIC measured deformations by comparing them with deformations measured using single-point laser Doppler vibrometry (LDV), establishing a comprehensive assessment of the TM's dynamic response and potential fracture mechanics under blast. Finally, we test our approach with 3D-printed TM-like samples and a real cadaveric human TM. This methodology lays the groundwork for further investigations of blast-related auditory damage and the invention of more effective protective and medical solutions.

Impact of Surface Finishing on Ti6Al4V Voronoi Additively Manufactured Structures: Morphology, Dimensional Deviation, and Mechanical Behavior

Additively manufactured medical devices require proper surface finishing before their use to remove partially adhered particles and provide adequate surface roughness. The literature widely investigates regular lattice structures—mainly scaffolds with small pores to enhance osseointegration; however, only a few studies have addressed the impact of surface finishing on the dimensional deviation and the global and local mechanical responses of lattice samples. Therefore, the current research investigates the impact of biomedical surface finishing (i.e., corundum sandblasting and zirconia sandblasting) on Voronoi lattice structures produced by laser powder bed fusion (LPBF) with large pores and different thicknesses on the surface morphology and global and local mechanical behaviors. MicroCT and SEM are performed for the assessment of dimensional mismatch and surface evaluation. The mechanical properties are investigated with 2D digital image correlation (DIC) in quasi-static compression tests to estimate the impact of surface finishes on local maps of strain. In the quasi-static tests, both the global mechanical performances, as expected, and local 2D DIC strain maps were mainly affected by the strut thickness, and the impact of different surface finishings was irrelevant; on the contrary, different surface finishing processes led to differences in the dimensional deviation depending on the strut thickness. These results are relevant for designing lattice structures with thin struts that are integrated into medical prostheses that undergo AM.

Damage monitoring on inter-lamination of GFRP via the resistance change of the MWCNT@GF sensor

The paper aimed to investigate the performance of multi-walled carbon nanotube-coated GF (MWCNT@GF) sensors on interlayer shear damage monitoring and sensing capability of glass fiber-reinforced polymers (GFRPs) based on the resistance change under short beam shear (SBS) load. The MWCNT@GF sensor, manufactured by physical vapor deposition (PVD), was embedded into the neutral layer of laminates to form an in-situ sensing network in different directions and positions. “The MWCNT@GF sensor, manufactured by physical vapor deposition (PVD), was embedded into the neutral layer of laminates to form an in-situ sensing network.” “With the help of Keithley 2700 programmable electrometer and the 3D-digital image correlation(3D-DIC), monotonic and cyclic tests were carried out.” The monotonic test found that the off-axis sensor is more sensitive to shear failure than the on-axis sensor because of its lower shear strength. In addition, the qualitative relationship between shear damage and relative resistance was established by selecting crucial moments. In the cyclical test, the relative resistance of off-axis sensors presented a cyclic mode under cyclic load. Furthermore, the relative resistance under the first 20 cyclic loads was similar to that under monotonic loads. “Furthermore, the relative resistance under the first 20 cyclic loads was similar to that under monotonic loads, which shows that the sensor has superior sensing ability. Finally, the quantitative relation between shear damage and relative resistance was established.” “That means MWCNT@GF sensors can be used to reasonably evaluate the damage state and further evaluate the service performance, reliability and remaining life of the structure.”

Short humeral stem in total shoulder arthroplasty does not jeopardize primary implant stability

BackgroundThe trend of the modern humeral components in total shoulder arthroplasty (TSA) is towards shorter and shorter humeral stems. However, the question remains whether short uncemented stems can provide the same implant stability as long stems. This study aimed to evaluate and compare the torsional primary stability, and the pull-out extraction force of both a long and a short version of the same stem. Materials and MethodsTen humeral components (five long-stem and five short-stem) were press-fitted into ten synthetic composite humeri. A torsional load was applied to generate the most critical loading condition. The specimens were loaded with 100 cycles between 2 Nm and 10 Nm, at 1 Hz. A 3D Digital Image Correlation system was used to measure the relative displacement between the prosthesis and the host bone during the test. After completing the torsional test, the pull-out force was measured. Differences between the long and short-stem on the biomechanical parameters (permanent migrations, inducible micromotion, and extraction force) were tested with the non-parametric Mann-Whitney test (p<0.05). ResultsThe main rotational inducible micromotion was around the craniocaudal axis. No significant differences were found between the rotational permanent migrations of the long- and short-stem around the craniocaudal (p=0.421), anteroposterior (p=0.841), and mediolateral axes (p=0.452). No significant differences were found between the rotational inducible micromotions of the long- and short-stem around the craniocaudal (p=0.222), anteroposterior (p=0.420), and mediolateral axes (p=0.655). No significant differences were found between the permanent translations of the long- and short-stem the along craniocaudal (p=0.341), anteroposterior (p=0.420), and mediolateral (p=0.429) directions. No significant differences were found between the translations of the long- and short-stem in terms of inducible translation in the craniocaudal (p=0.547), anteroposterior (p=0.999), and mediolateral axis (p=0.285). Similar extraction force (p=0.35) was found. Discussion and ConclusionNo statistically significant difference was found between the long-stem and short-stem implants. These results show that short uncemented stems can provide adequate primary mechanical stability. As the long-stem version of this stem is already clinically used, the present findings suggest that the short-version can be reasonably expected to deliver similar outcomes in terms of implant stability.

Damage identification in composite structures using high-speed 3D digital image correlation and wavelet analysis of mode shapes

ABSTRACT In this study, the damage identification procedure combining the advantages of high-speed 3D digital image correlation (DIC) that is used for modal analysis and wavelet-based processing algorithm is presented. The proposed procedure has been successfully validated on sandwich composite structures with internal damage of a core and impact damage, and its performance was demonstrated by detection, localisation, and identification of shapes of damage in tested structures, comparable to the results from scanning laser Doppler vibrometry (SLDV). The effectiveness in damage identification was achieved by the development of processing algorithm of acquired mode shapes, which uses a 2D double-density directional wavelet transform with increased sensitivity with entropic weights allowing to automatically select those wavelet coefficients and mode shapes, which are most sensitive to damage. The procedure presented in this paper demonstrates the performance of 3D DIC for damage identification as a cost-effective alternative to the procedures based on SLDV measurements.

Mechanical properties and damage constitutive relationship of microwave irradiation of granite under uniaxial compression

Microwaves have great potential to increase the efficiency of hard rock breakage during mechanical excavation in engineering. This study conducted uniaxial compression tests on granite specimens after microwave irradiation at 4.85 kW. The results demonstrated a linear decrease in uniaxial compressive strength and elastic modulus correlating with increasing irradiation durations. Acoustic emission data indicated increased normalized crack closure stress and decreased normalized crack initiation and damage stress, suggesting complex crack propagation and evolution patterns under microwave influence. 3D Digital Image Correlation revealed that as heating time increased, the macrocrack leading to specimen failure shifted from being load-dominated to involving both load and microwave-induced thermal cracks. A simple four-parameter damage constitutive model for granite (a 1, r 1 , a 2, and r 2) effectively described the damage evolution under the coupling effect of microwave and uniaxial load. The model accurately characterized the complete stress–strain curves, including both microcrack compaction and post-peak stages, revealing that initial damage escalates with longer heating, though the progression rate decreases.

Elastic properties identification of a bio-based material in tertiary packaging: Tools and methods development

This study focuses on the use of bio-based materials for structural purposes in the packaging field, which requires the identification of their mechanical properties at a representative scale. The mechanical properties of bio-based materials are more variable than those of traditional composite materials. In a standard characterization approach using elemental coupons under uniaxial loading, the variability depends on the chosen representative elementary volume (REV), free edges, boundary conditions, etc. for elastic properties that are not identified for representative working conditions; this could lead to the ineligibility of these bio-based materials as structural materials. This paper contributes to the debate on how to study the response of bio-based materials within a structure, here a packaging structure as a logistic unit (LU) subjected to a compressive load simulating storage and stacking conditions. In the set of tools and methods for the design of packaging materials made of bio-based materials, an elastic nonlinear geometric finite element model (FEM) and an experimental approach are presented. The FEM allows the numerical identification of zones of interest within the LU. Inevitably, the FEM classically requires input data which are elastic properties of the equivalent homogeneous material. The design of the FEM is based on a calculation-test approach using an existing reference LU and it can be summarized in two main steps. The first step concerns the development of a FEM able to restore the experimental conditions of vertical compression imposed by transport standards for packaging. The second step is based on updating the input properties of the FEM by reverse identification, to achieve the representative working condition properties, using experimental results obtained on the existing reference LU. For the reverse identification a multi-scale investigation is mandatory. For this purpose, the linear elastic part of the load/vertical displacement curves (at the LU stiffness scale) and the displacement and strain fields measured (at the local LU scale) by 3D digital image correlation (3D DIC) are evaluated. Then, FEM property updating is carried out by reducing the deviation of displacement/strain fields between FEM and experimentally measured results (3D DIC). Finally, we explain how FEM and 3D DIC help in decision-making by allowing the recognition of zones of interest in a phase of design of new LUs with the concept of Multi-Instrumented Technological Evaluator (MITE).

From quasi-static to dynamic: Experimental study of mechanical and fracture behaviour of epoxy resin

Epoxy polymers are extensively used in various engineering applications such as aerospace, defence, sports, automotive etc. This article focuses on the in-depth mechanical characterisation of EPOFINE®-1564, a Bisphenol-A-based liquid epoxy resin under various loading conditions. To predict the tensile and compressive behaviour of the representative epoxy resin, quasi-static experiments were performed in the range of 10−4 to 10−2s−1 on Universal testing machine (UTM) while the dynamic experiments were conducted using Split Hopkinson Pressure Bar (SHPB) for high strain rates (1136–2833 s−1). In this study, 3D Digital Image Correlation (DIC) was also used to evaluate the specimen's full-field displacement profile over a wide range of strain rates. Analysis of various mechanical properties such as elastic modulus, yield strength, and ultimate strength, revealed that the epoxy polymer is strain rate dependent within the considered strain rate range. For understanding the fracture behaviour, three-point bend (TPB) experiments were also carried out for both quasi-static (1–10 mm/min) as well as dynamic (10–15 m s-1) regimes. Dynamic fracture experiments were performed using the modified Hopkinson Pressure Bar (MHPB). The fracture toughness was determined through load vs crack mouth opening displacement (CMOD). Fracture toughness was found to increase with the displacement rate due to the significant plastic deformation under quasi-static range. Conversely, it was found to decrease under dynamic loading because of absence of plastic deformation resulting in brittle fracture. The fracture surface of the specimen was examined through a high magnification digital microscope.

RealPi2dDIC: A low-cost and open-source approach to In-situ 2D Digital Image Correlation (DIC) applications

In this current work an open-source 2D Digital Image Correlation (DIC) tool, RealPi2dDIC, is presented to monitor in-situ full field deformation and strain responses of structures during loading. This software is coded in Python3 and uses Raspberry Pi as the computation and Pi camera as the imaging device. This low-cost approach to in-situ DIC analysis enables its application in a broad field of research and industry problems where 2D strain field tensor is one of the principal interests of study. This code is provided with an interactive user interface (UI) making it user friendly and easy-to-use. Furthermore, RealPi2dDIC offers a simple software architecture which can be adopted, modified and extended to suit users’ purpose.

Adaptive matching strategies for 3D digital image correlation in strain measurement of an aerostat envelope

To address the limitations of two-dimensional digital image correlation (2D-DIC) in measuring strain on the aerostat envelope, the more precise 3D-DIC has been introduced to handle curved surfaces. However, the increased computational load of 3D-DIC requires more efficient correlation strategies. This paper evaluates three basic matching strategies and introduces two adaptive strategies to enhance the efficiency of 3D-DIC. The experimental results show that the adaptive composite matching (ACM) strategy automatically switches strategies based on deformation, improving the matching correlation. Meanwhile, the adaptive grouping matching (AGM) strategy dynamically adjusts image groups based on real-time data, optimizing the computational speed and enhancing measurement flexibility. These strategies provide crucial support for the application of 3D-DIC in the monitoring aerostat envelope strain, especially in managing significant or uneven deformations.

3D mode shapes characterization under hammer impact using 3D-DIC and phase-based motion magnification

Modal analysis constitutes a fundamental aspect of structural investigation within diverse engineering domains, encompassing sectors such as automotive, wind energy, and aerospace. The prominence of high-frequency excitation loads, exemplified by the combustion phenomena in liquid rocket engines, necessitates an in-depth examination of the high-frequency vibrational response within structural components. However, the complexity of evaluating high-frequency vibrations arises from the negligible displacement associated with these responses. When using an optical full-field measurement system based on a high-speed camera for vibration measurement, it is usually severely affected by noise. Direct analysis of raw data using an optical measurement system (3D-DIC) is not feasible. In this paper, we combine phase-based motion magnification and digital image correlation methods to obtain the high-frequency vibration modes of the structure. 3D-DIC(3D Digital Image Correlation)analysis is performed on the magnified images to quantify the out-of-plane vibration modes of the structure. Using the cantilever beam as an example, the first five out-of-plane vibration mode shapes were separated from the response video under a single hammer excitation. Especially the 5th order natural frequency is as high as 3503 Hz, and the corresponding structural response was below the noise floor of the camera system. The vibration mode results obtained by this method are highly consistent with the vibration modes obtained by the 3D-SLDV(3D Scanning Laser Doppler Vibrometer) method. Finally, this method was applied to identify the out-of-plane vibration modes of real engine pipe. The combination of motion magnification techniques and DIC can enhance the capability of traditional 3D-DIC, which is beneficial for high-frequency structural identification. Future research could concentrate on optimizing motion amplification factors for different structures and loads, and creating automated algorithms for analyzing and visualizing amplified motion data in real time.

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

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

On the anisotropic fracture behaviour of AA2050-T84 thick plate

Anisotropy in the fracture behaviour of AA2050-T84 was investigated using 2D digital image correlation (DIC)-assisted 3-point bending fracture toughness test on specimens with crack propagation direction oriented along the normal direction (ND) and rolling direction (RD). The tensile properties along the RD indicated slightly higher yield strength (482 ± 8 MPa) than ND sample (469 ± 9 MPa), while the fracture toughness in terms of energy release rate was higher when the notch was oriented along the ND (35.3 ± 1 kJ/m2) compared to the RD (18.5 ± 0.9 kJ/m2). Fractography of the fractured surfaces and detailed electron backscatter diffraction (EBSD) analysis of the microstructure along crack paths unveiled higher crack tortuosity with extensive secondary cracking in the TD-ND specimen than in the TD-RD. DIC measurements clearly showed a larger deformation zone for the TD-ND specimen also as which corroborated the plastic zone size determined using linear elastic fracture mechanics (LEFM). Additionally, the crystallographic model of tilt and twist angle differences between the neighbouring grains was employed to explain the increase in crack path tortuosity and higher dissipation of plastic work contributing to superior fracture toughness for the TD-ND sample.

Strain Field Development, Fracturing, and Gas Ejection in Decoupled Charge Blasting Using Granite Cylinders

This study explored the fracture process of granite cylinders with a centric charge, varying decoupling ratios by conducting laboratory-scale experiments and numerical simulations. In experiments, the three-dimensional (3D) digital image correlation (DIC) technique was employed, using frames captured by two synchronized high-speed cameras. This instrumentation permitted the observation of full-field strain variation, the development of fractures, and gaseous products escaping from the cylinders’ surfaces. Granite cylinders measuring 240 mm in diameter and 300 mm in length served as specimens in blasting experiments, and each specimen had a charge of approximately 3 g. Specimens had a centric blasthole with a diameter of either 10 mm, 14 mm, or 20 mm. The corresponding decoupling ratio varied from 1.8 to 3.6, and the gap between the charge and the blasthole wall was filled with water or air. The experimental results showed that: (1) specimens with decoupling ratios of 1.9 and 2.6 exhibited initial strains on the cylindrical surface between 20 μs and 40 μs. (2) Specimens with water-filled blastholes developed fractures faster and in a denser manner compared to those with air-filled blastholes. In addition, fractures resulting from air-filled blastholes appeared smoother than those from water-filled blastholes. (3) The gas ejection time for the air-filled blasthole remained basically consistent across decoupling ratios ranging from 1.5 to 3.61, varying between 400 μs and 520 μs. The utilization of water-filled blastholes effectively minimized the escape of gaseous products from the cylindrical surface. Numerical simulation conducted with LS-DYNA exhibited results that aligned well with the observed fracture patterns in the experiments. This study aims to provide a better understanding of the fundamental mechanisms of rock behaviors in decoupled charge blasting.