Non-contact Digital Image Correlation Technique Research Articles

The yielding behavior and plastic deformation of oxygen-free copper under biaxial quasi-static and dynamic loadings

This study investigated the yield behavior of oxygen-free copper under complex stress states and different loading rates. An optimized cruciform specimen and a novel electromagnetic biaxial split Hopkinson bar (EBSHB) were used to perform the dynamic biaxial tension tests at three different load ratios. The non-contact digital image correlation technique was adopted for strain measurement. Quasi-static and dynamic yield surfaces were obtained. Classical yield criteria, including the Tresca and von Mises yield criteria, were evaluated based on the experimental results. The von Mises criterion is found to provide better prediction of the yield surface under both quasi-static and dynamic loadings. The Johnson-Cook model from uniaxial test results provides a moderate prediction for experimental curves, while that from biaxial test results shows better prediction. Dynamic biaxial tests are proven necessary to acquire the constitutive models that can accurately describe the mechanical properties of copper under complex stress states.

Experimental analysis of control technology and deformation failure mechanism of inclined coal seam roadway using non-contact DIC technique

The deformation and failure forms of inclined coal seam roadway under the joint action of dip angle and various geological conditions are complex, and there is a lack of targeted support measures, which brings great problems to the stability control of roadway surrounding rock. In order to safely and economically mine inclined coal seams, taking the engineering geology of Shitanjing No. 2 mining area as the background, and the physical similarity model of right-angle trapezoidal roadway in inclined coal seam, in which the non-contact digital image correlation (DIC) technology and the stress sensor is employed to provide full-field displacement and stress measurements. The deformation control technology of the roadway surrounding rock was proposed, verified by numerical simulation and applied to engineering practice. The research results show that the stress and deformation failure of surrounding rock in low sidewall of roadway are greater than those in high sidewall, showing asymmetric characteristics, and the maximum stress concentration coefficients of roadway sidewall, roof and floor are 4.1, 3.4 and 2.8, respectively. A concept of roadway "cyclic failure" mechanism is proposed that is, the cyclic interaction of the two sidewalls, the sharp angles and roof aggravated the failure of roadway, resulting in the overall instability of roadway. The roadway sidewall is serious rib spalling, the roof is asymmetric "Beret" type caving arch failure, and the floor is slightly bulging. On this basis, the principle of roadway deformation control is revealed and asymmetric support design is adopted, and the deformation of roadway is controlled, which support scheme is effective.

Assessment of load distribution mechanism in geocell reinforced foundation beds using Digital Imaging Correlation Techniques

The pressure distribution below geocell reinforced foundation beds depends on several factors like height of geocell, weld distance (pocket size), infill material, etc. This paper describes a method to determine the load dispersion mechanism through a geocell layer using a non-contact Digital Image Correlation technique. Series of plate load tests were performed in a test tank having plan dimensions of 0.6 m × 0.6 m and height of 0.65 m. The loading was applied through a strip footing of width 120 mm. Two miniature geocells having heights of 60 mm and 75 mm were used for reinforcing the base layer of the foundation section. The studies were performed with two types of geocells having smooth and rough surfaces. The relative density (RD) of the base and subgrade layers were maintained as 80% and 40%, respectively during the tests. The movement of soil particles was recorded by capturing images at different stages of the test. The images were processed using a Digital Image Correlation (DIC) software to obtain displacement contours and vectors. The results show that the geocells distribute the load over a wide area of the foundation soil. The dispersion angle was found to depend on the height of geocell and the roughness of the geocell surface. The load dispersion angles obtained from Digital Image Correlation analyses of unreinforced and reinforced sections have been compared with similar published results.

The role of brass texture on the deformation response of 7075-T651 aluminum alloy under equi-biaxial tension

Cruciform specimen is utilized to study the influence of equi-biaxial stress state on the plastic strain response of AA7075-T651 alloy until fracture. The failure ductility as a function of stress state is evaluated using non-contact digital image correlation technique. The distinct biaxial deformation behavior in contrast to uniaxial response is attributed to strong crystallographic texture developed during prior hot-rolling reduction. The weakening of initial brass texture upon equi-biaxial deformation is also evident from the orientation distribution analysis. Increased activity of grain boundary assisted cracking due to increased stress triaxiality due to biaxial loading is evident, when compared to uniaxial stress state. • Cruciform specimen is used to capture the plastic strain response of 7075-T651 aluminum alloy until fracture. • Severe reduction in ductility with concomitant improvement in yield strength observed under biaxial condition. • Increased occurrence of grain-boundary assisted cracking corroborates decreased ductility under equi-biaxial stress state. • Brass texture component {0 1 1} < 5 3 ‾ 3> contributed to the observed biaxial strengthening effect.

Experimental analysis of progressive failure behavior of rock tunnel with a fault zone using non-contact DIC technique

Geological discontinuities govern the strength and deformation of rock mass and play an important role in the stability of geotechnical excavations, such as tunnels, caverns, slopes, and mines. In this paper, the failure mechanism of a tunnel in the vicinity of a fault zone is investigated by physical model tests with dimensions of 3 m × 2.4 m × 0.4 m, in which the non-contact Digital Image Correlation (DIC) technique is employed to provide full-field displacement measurements. Results show that the fault zone near the tunnel shoulder has a significant influence on the stability of the surrounding rock, in terms of strain localization and failure initiation. With the increase of surcharge loading, cracks initiate at the two sidewalls, following by the initiation of cracks at the left shoulder and the crown. Cracks propagate to the fault zone eventually, leading to asymmetrical collapse. The stress loosening zone (SLZ) in the surrounding rock after tunnel excavation is significantly influenced by the fault zone near the left shoulder of the tunnel, showing the occurrence of stress redistribution. It is recommended to implement reinforcement in the rock mass between the tunnel and the fault to improve the stability.

In situ estimation of fatigue crack parameters by digital image correlation under cyclic loading with single overload

The paper represents the investigation of crack propagation in aluminium alloy AA2024 in a case of constant cyclic loading with single overload. The parameters of the process were evaluated by means of optical and noncontact digital image correlation technique which allows precise in situ measurements and provides local strain data. There have been analysed strain fields, local strains at the crack tip and crack closure level in order to reveal the effect of overload on crack growth parameters. Results are consistent with published data and developed mathematical models - the highest impact is emerged when crack extended into overload plastic zone by 30%.

Effects of cycle times and C-rate on mechanical properties of copper foil and adhesive strength of electrodes in commercial LiCoO2 LIBs

It is important to appraise the evolution of mechanical properties of current collectors and the adhesive strength of electrodes to reveal the chemical-mechanical coupling failure mechanism of lithium-ion batteries (LIBs), and to improve their cycling performance and cycling life. In this work, the mechanical properties of copper foil, anode, and cathode of commercial LIBs were studied under different cycling conditions by means of tensions with the aid of non-contact digital image correlation technique. It is found that different electrochemical cycle times and C-rates have great influence on the degradation of the mechanical properties of copper foil and the interfaces of graphite/copper foil and LiCoO2/alumina foil. The changes in elastic modulus, fracture strength and elongation of the copper foil were analyzed at 0.5C, 0.8C and 1.0C within 200 cycles, respectively. The adhesive strength of graphite/copper foil changes from its initial value 285.6 kPa to 55.5 kPa after 200 cycles at 1.0C, and the adhesive strength of LiCoO2/alumina foil decreases from its initial value 841.2 kPa to 132.8 kPa after 200 cycles at 1.0C.

Experimental Study on the Mechanical Properties of Porcine Cartilage with Microdefect under Rolling Load

Objectives To investigate the mechanical responses of microdefect articular cartilage under rolling load and find out the failure rule. Methods Rolling load was applied to the porcine articular cartilage samples with rectangular notches of different depths. The displacement and strain near the notches were obtained by the noncontact digital image correlation technique. Results The strain value and peak frequency around the notch increased; the maximum equivalent strain value could be observed at both bottom corners of the notch; the equivalent strain value first increased and then decreased at the points in the superficial and middle layers with the increase of rolling velocity; the points in the deep layer were less affected by rolling velocity; the equivalent strain value of the points in the superficial layer declined after rising with the increase of defect depth, while a decreased trend could be found for the points in the middle and deep layers. Conclusions The shear strain, which rose with the increase in defect depth, was the main factor in cartilage destruction. The cartilage tended to be destructed firstly at the bottom corner of the defect. Rolling velocity showed significant effects on superficial and middle layers. Cartilage had the ability to resist destruction.

Deformation behavior of commercially pure (CP) titanium under equi-biaxial tension

Biaxial tensile tests on commercially pure titanium were carried out using cruciform specimen geometry and the effect of biaxial tensile stress state on the mechanical properties was discussed. An optimum cruciform specimen geometry obtained using a commercial FE code was subjected to equi-biaxial tensile loading and the load-strain response was captured using data acquisition system. In addition, non-contact digital image correlation technique was employed for the measurement of failure strain. It is observed that the ultimate tensile strength approximately doubled and the failure strain decreased in contrast to uniaxial mechanical properties of commercially pure titanium. Increased effective modulus under biaxial condition is justified based on the generalized Hooke’s relation. Strong basal and split-basal texture components of as-received sample resulted in biaxial strengthening effect. Significant textural evolution observed upon biaxial deformation can be attributed to constrained deformation under such stress state.

The fracture response of blended formulations containing limestone powder: Evaluations using two-parameter fracture model and digital image correlation

The fracture response of mortars in which OPC is partially replaced by limestone or a combination of limestone and fly ash/metakaolin (i.e., for total OPC replacement levels of 20% and 35% by volume) is reported. The blended mortars demonstrate fracture parameters (fracture toughness, KICS and critical crack tip opening displacement, CTODc, determined using the two-parameter fracture model, TPFM) that are comparable to or better than those of pure OPC formulations in spite of having slightly lower compressive strengths than the OPC systems. The ternary blends containing limestone and metakaolin at 20% OPC replacement show the best performance: a consequence of the beneficial limestone–alumina synergy that has been previously established. The strain energy release rates also show trends that are in line with the other fracture parameters. The fracture parameters for selected mixtures evaluated through a non-contact digital image correlation technique are found to correspond well to those determined from TPFM. The outcomes highlight that improved ductility can be attained through the judicious use of limestone and synergistic OPC replacement materials.

Effects of Joint Thickness, Adhesion and Web Shells to the Face Shell Bedded Concrete Masonry Loaded in Compression

The Australian masonry standard allows either prism tests or correction factors based on the block height and mortar thickness to evaluate masonry compressive strength. The correction factor helps the taller units with conventional 10 mm mortar being not disadvantaged due to size effect. In recent times, 2–4 mm thick, high-adhesive mortars and H blocks with only the mid-web shell are used in masonry construction. H blocks and thinner and higher adhesive mortars have renewed interest of the compression behaviour of hollow concrete masonry and hence is revisited in this paper. This paper presents an experimental study carried out to examine the effects of the thickness of mortar joints, the type of mortar adhesives and the presence of web shells in the hollow concrete masonry prisms under axial compression. A non-contact digital image correlation technique was used to measure the deformation of the prisms and was found adequate for the determination of strain field of the loaded face shells subjected to axial compression. It is found that the absence of end web shells lowers the compressive strength and stiffness of the prisms and the thinner and higher adhesive mortars increase the compressive strength and stiffness, while lowering the Poissons ratio

Effects of joint thickness, adhesion and web shells to the face shell bedded concrete masonry loaded in compression

The Australian masonry standard allows either prism tests or correction factors based on the block height and mortar thickness to evaluate masonry compressive strength. The correction factor helps the taller units with conventional 10 mm mortar being not disadvantaged due to size effect. In recent times, 2-4 mm thick, high-adhesive mortars and H blocks with only the mid-web shell are used in masonry construction. H blocks and thinner and higher adhesive mortars have renewed interest of the compression behaviour of hollow concrete masonry and hence is revisited in this paper. This paper presents an experimental study carried out to examine the effects of the thickness of mortar joints, the type of mortar adhesives and the presence of web shells in the hollow concrete masonry prisms under axial compression. A non-contact digital image correlation technique was used to measure the deformation of the prisms and was found adequate for the determination of strain field of the loaded face shells subjected to axial compression. It is found that the absence of end web shells lowers the compressive strength and stiffness of the prisms and the thinner and higher adhesive mortars increase the compressive strength and stiffness, while lowering the Poisson's ratio.