Digital Image Correlation Test Research Articles

3D printed concrete incorporating waste rubber: Anisotropic properties and environmental impact analysis

The recycling and reuse of solid wastes mark the construction industry's development towards sustainable and green technologies. 3D printing technology using recycled solid materials is in great demand for intelligent and low-carbon construction. This paper incorporates crumb rubber (0–1 mm) into the printing ink and analyses the fresh and hardened properties. The results showed that the flowability was positively correlated with rubber ratio but negatively with fiber content. R40F15 (40% rubber and 1.5% fiber) obtained the optimal flowability for 3D printing, which remained above 15 mm for 30min. The compressive strength peaked when incorporating 1.5% fiber, while the flexural strength reached the bottom. X direction generated the highest compressive strength in the whole anisotropic tests, followed by the Y and Z directions. The highest strengths of 1.5% and 2.0% fiber content were 69.45 MPa and 64.5 MPa, incorporating 20% rubber. Thus, surfaces anticipated to bear higher loads in compression should be aligned with the X-axis or, at a minimum, avoid alignment with the Z-axis for optimal structural performance. Y direction obtained the highest flexural strength in all anisotropic tests when incorporating 1.5% fiber. Results from digital image correlation test supported that fiber tended to agglomerate in the Y direction. Besides, the environmental analysis was conducted in this paper to quantitively calculate the impacts of all raw materials to the environment.

Characterization on the mesostructural distribution of asphalt mixtures via digital image processing and relation to macroscopic performances

The distribution characteristics of the mesostructure of asphalt mixtures have an important influence on the macroscopic performance of asphalt mixtures. In this study, by means of industrial computed tomography and voxel analysis, the distribution of voids and skeleton microstructure of asphalt mixture is characterized from multiple perspectives. The relationship between mesostructural characteristic parameters and macroscopic properties of asphalt mixtures was established by the indirect tensile test, uniaxial compression test, and digital image correlation test. The results show that the mesostructural distribution of the voids of different types of asphalt mixtures shows a certain degree of transverse isotropy. Air voids content and fractal dimension of voids are the mesostructural characteristic parameters that affect the cracking resistance of asphalt mixtures at low temperatures. The air voids content has a negative exponential relationship with the strength of asphalt mixture. When the void fractal dimension is 1.3, the splitting tensile strength of asphalt mixture reaches the maximum value. Skeleton structure is a mesostructure characteristic parameter that affects the high temperature stability of asphalt mixture. The lower voids in coarse aggregate skeletons and degree of anisotropy are positively correlated with the uniaxial compressive strength. After voids in coarse aggregate skeletons are lower than 35 %, the uniaxial compressive strength of asphalt mixture is significantly improved. The proposed skeleton evaluation index can effectively characterize the material composition differences of different types of asphalt mixtures. The strain cloud diagram of the digital correlation experiment shows the place where the void distribution first reached the maximum strain of about 0.003 during loading, and the high strain area corresponds to the void centroid distribution. The air voids centroid distribution is the mesostructural characteristic parameter of the indirect tensile strain distribution.

Experimental study on crack propagation process of rock‐concrete interface in hot‐dry curing environment at different temperatures

AbstractThe effect of hot‐dry environment in the high‐temperature geothermal tunnel increases the initial defects on the bonding surface of the shotcrete and surrounding rock, which intensifies the generation and development of interface cracks. In this context, a wedge splitting test is used to study the fracture performance of the rock‐concrete interface in the hot‐dry environment at different temperatures. Based on the digital image correlation test, the development law of interface cracks is observed, the determination method of interface crack size is introduced, and the evolution process of interfacial fracture process zone is analyzed. The results show that the peak loads and the interface fracture energies of the specimens under the hot‐dry environment are significantly smaller than the standard curing environment, and decrease with the increase of temperature. In the standard curing environment, the cracks rapidly spread to the edge of the specimen near the peak load, while the cracks expand more slowly in the hot‐dry environment. The opening displacement of interface crack is linearly distributed along the height of specimen, and its value is much larger than the sliding displacement. The maximum interface fracture process zone length in hot‐dry environment is greater than that in standard curing environment.

Fracture Characterization of Advanced High Strength Steel USS CR980XG3 Using Phase-Field Diffusive Approach in Ductile Solids

In this work, the utilization of a phase-field ductile fracture model in the failure analysis of advanced steels is investigated. The importance of advanced steels is potentially proven, for instance in automotive industry, due to its light weight, which entails the crucial role of fracture analysis in these structures. A third generation advanced high strength USS CR980XG3™️ AHSS material is considered to perform fracture analyses. For this purpose, the necessary data regarding the stress distribution and fracture patterns from digital image correlation tests are utilized for subsequent numerical experimentations.A recent phase-field model of ductile fracture is employed herein for the analysis of crack advance in this class of materials. The significance of the choice of material properties using this model is shown through the analysis of an experimental fracture benchmark called Shear Fracture specimen, through assessment of crack evolution and force diagrams.

In-situ investigation of deformation behavior in additively manufactured FeCoCrNiMn high entropy alloy

Additively manufactured high entropy alloys (AMed HEAs) usually have many distinctive microstructures, which will have a great impact on the mechanical properties. Revealing the role of different microstructures in the deformation process can provide guidance for the microstructure design of AMed HEAs. This paper used in-situ electron backscattered diffraction and digital image correlation tests to investigate the deformation behaviors of FeCoCrNiMn HEAs fabricated by laser directed energy deposition. The as-built FeCoCrNiMn HEAs have two kinds of microstructures: equiaxed and columnar. The equiaxed microstructure has no texture, the grain size is 28 μm, and the grain boundary misorientation conforms to theoretical distribution, whereas the columnar microstructure is composed of <101> oriented and coarse grains, and has a large number of low angle grain boundaries. In the deformation processes, <101> oriented grains are more prone to rotational deformation than <001> and <111>, but the tensile strain produced by < 101> is lower than <001> and higher than <111>. And compared with the coarse grains, the fine grains tend to coordinate the deformation from surrounding grains through grain rotation, and the strain concentrations are more readily to emerge in fine-grain regions. The average grain boundary geometric compatibility factor (m') of equiaxed microstructure is 0.39, and that of columnar microstructure is 0.57, so the grain boundaries of equiaxed microstructure have a more effective role in impeding dislocations. In addition, the statistical result shows that the value of m' is related to the grain boundary misorientation.

Direct strain distribution and finite-element-analysis simulation of the bonding interface of bamboo laminated lumber with ultrasound-treated bamboo strips

An ultrasonic cavitation treatment was used to increase the permeability of phenol formaldehyde resin adhesive on the surface of bamboo strips, and two-ply laminated bamboo lumber was manufactured. The strain distribution along the bamboo interface under stretching conditions was investigated using the digital image correlation technique. The effect of the ultrasonic treatment on the bamboo strips in terms of the shear strain of the laminated bamboo lumber was investigated, and a finite-element analysis for the bonding interface was carried out to evaluate whether the deformation measurement could predict the mechanical behavior differences of the laminated bamboo lumber. The digital image correlation and shear strength results show that the strain was lower in the bamboo bonding interface after ultrasonic treatment and the shear strength was enhanced due to the increased adhesive penetration. The digital image correlation measurement and finite-element analysis simulation both showed that stress was more concentrated, and the strain value and strain zone width was higher in the carbonized bamboo bonding interface than in the bleached bamboo bonding interface. The finite-element analysis results appeared to be in agreement with the digital image correlation test results.

Cross section deformation of heterogeneous rectangular welded tube in rotary draw bending considering different yield criteria

Heterogeneous rectangular welded tube has serious anisotropy of parent metal and weld zone, in order to improve the prediction accuracy of cross-section deformation of tube in rotary draw bending (RDB), it is necessary to select the appropriate yield criterion to describe the anisotropic characteristics of heterogeneous rectangular welded tube. So the anisotropic parameters of Hill’48 and Barlat’89 yield criteria of parent and weld zone were obtained by using the digital image correlation test, then FE models of RDB of rectangular welded tube using different yield criteria were established. Based on these established FE models, the cross section deformation of thin-walled heterogeneous rectangular welded tube in RDB considering different yield criteria was researched. The results showed that, for the height and width deformation ratio of rectangular welded tube, the simulated results obtained by Mises, Barlat’89 and Hill’48 yield criteria in sequence, gradually increased to experimental results, this indicated that Hill’48 can well describe the anisotropic characteristic of rectangular welded tube. Further, under the condition of different bending angles and different core numbers, the maximum height deformation ratio obtained by Mises, Barlat’89 and Hill’48, successively, gradually increased to experimental results, which meant that Hill’48 anisotropic yield criterion was the most suitable one to predict cross section deformation of QSTE700 rectangular welded tube in RDB.

A comparative study between the mechanical and microstructural properties of resistance spot welding joints among ferritic AISI 430 and austenitic AISI 304 stainless steel

In this study, 1.5-mm-thickness ferritic AISI 430 and austenitic AISI 304 stainless steel are resistance spot-welded by combining 304/304, 304/430 and 430/430. The dissimilar 304/430 nugget displays a strong texture and consists of α-ferrite columnar grains, with some γ-austenite and α′-martensite dispersed over the grains’ boundary zone. Lap-shear tests are performed for each welding combination under different parameters. The results show that the interfacial failure to pull-out failure mode transition tendency is in the following order: 304/430>304/304>430/430. This is because: (1) the nugget of 304/430 samples are harder than that of the 304/304 samples, which makes the former less likely to fracture under nugget plastic failure; (2) the 304/430 nugget samples possess higher local toughness than the 430/430 samples, a property that makes 304/430 joints resistant to fracture under nugget brittle rupture. Besides, the 304/304 joints possess high energy absorption in the lap-shear test, even for interfacial failure mode samples. This is confirmed in the digital image correlation tests which show the presence of a massive plastic deformation in the 304/304 joint fracture in interfacial failure mode.

Tensile and fracture characterization using a simplified digital image correlation test set-up

Digital image correlation (DIC) is now a popular and extensively used full-field metrology technique. In general, DIC is performed by using a turnkey solution offered by various manufacturers of DIC. In this paper, a simple and economical set-up for DIC is proposed which uses easily accessible digital single-lens reflex (DSLR) camera rather than industrial couple-charged device (CCD) cameras. The paper gives a description of aspects of carrying a DIC experiment which includes experimental set-up, specimen preparation, image acquisition and analysis. The details provided here will be helpful to carry DIC experiments without specialized DIC testing rig. To validate the responses obtained from proposed DIC set-up, tension and fatigue tests on specimens made of IS 2062 Gr. E300 steel are determined. Tensile parameters for a flat specimen and stress intensity factor for an eccentrically-loaded single edge notch tension specimen are evaluated from results of DIC experiment. Results obtained from proposed DIC experiments are compared with those obtained from conventional methods and are found to be in close agreement. It is also noted that the high resolution of DSLR allows the use of proposed approach for fracture characterization which could not be carried out with a typical turnkey DIC solution employing a camera of 2MP resolution.

Digital image correlation through image registration in the frequency domain

The present work analyses displacement field computations for several digital image correlation test cases obtained through the application of image registration in the Fourier domain. The applied method relies on the properties of the discrete Fourier transform with regard to the cross-correlation function to find the rigid displacement between two subsets. The computed displacement fields were compared to their analogous values obtained through a commercial digital image correlation code. The test cases cover both two-dimensional and three-dimensional digital image correlation and make use of the ability of the developed method to calculate the translation and rotation between subsets from images at different loading states, as well as its capacity to match subsets from two cameras of a stereo rig. The presented analysis aims to contribute to the investigation of the use of correlation in the frequency domain as the basis for an alternative to conventional digital image correlation which could provide advantages in terms of robustness and efficiency, particularly in field measurements, where the lack of control over lighting and other factors impacting image quality requires a system which is optimised towards low dependence on the optimal quality of these conditions.

Numerical Analysis of Macro-Scale Mechanical Behaviors of 3D Orthogonal Woven Composites using a Voxel-Based Finite Element Model

A study is conducted with the aim of developing voxel-based finite element method related to the whole fiber distribution for predicting the macro-mechanical properties of 3D orthogonal woven composites. For the rationality of this model, multi-scale finite element method, which is on the basis of the surface and interior representative volume cells, and digital image correlation tests are carried out. The results show that the proposed voxel-based finite element method is capable of precisely calculating the macro-level properties of 3D orthogonal woven composites, validated by the comparison the mechanical behaviors as well as the full-field strain fields.

Functionally graded Inconel 718 processed by additive manufacturing: Crystallographic texture, anisotropy of microstructure and mechanical properties

Additive manufacturing offers a unique way of anisotropic microstructure control with a high degree of design freedom. This study demonstrates that application of suitable process parameters and laser sources in selective laser melting may favour either one sharp single component texture, more uniformly distributed crystal orientation, or a combination of the above in a preferred gradient, which influence the mechanical properties. It is shown that transitions in microstructure, texture, and properties in fabricated Inconel 718 functionally graded components can be obtained at relatively small or large length scales, depending upon the functional gradient desired in a particular application. Results obtained by electron backscatter diffraction showed distinct regions of coarse elongated grains with a strong (001) orientation uniformly embedded in randomly distributed fine grained matrix. Mechanical tests in the form of hardness, tensile and in-situ digital image correlation tests showed steep transitions in the developed Inconel gradients. The observed mechanical properties were found to be primarily dependent on the grain size and texture and are superior to the cast samples for both laser sources. The developed process strategy can be further applied to design functional gradients with selected tailored properties and to account for directional anisotropy of solidified components.

Theoretical Analysis on the Measurement Errors of Local 2D DIC: Part I Temporal and Spatial Uncertainty Quantification of Displacement Measurements

AbstractThis paper presents a theoretical uncertainty quantification of displacement measurements by subset‐based 2D‐digital image correlation. A generalised solution to estimate the random error of displacement measurement is presented. The obtained solution suggests that the random error of displacement measurements is determined by the image noise, the summation of the intensity gradient in a subset, the subpixel part of displacement, and the interpolation scheme. The proposed method is validated with virtual digital image correlation tests.

Digital Image Correlation Test System with Automatic Transmission for Quasi-Brittle Material

To realize the automatic transmission for present digital image capture test system, a new system which consists of laptop computer, camera, fixing device and mechanical testing machine was presented and designed. The Monitor software, which was developed using MATLAB to realize automatic transmission function for the system, includes slow and high speed. The general stage and key stage for quasi-brittle materials can be effectively captured by the software. With MATLAB, the digital image correlation software (DIC) was developed. In DIC the first image is used as the base image. The images are sorted by photographing time (or file name), and the listing file is generated. The grid is drawn on the base image to divide the area into ‘facets’, the size of which can be adjusted between 1pixel and 100 pixels. Based on fast Fourier transform and convolution algorithm, the image comparison is realized and the deformation of the material is calculated. The designed system is applied to the compression test of a concrete specimen, and the results show that the system realizes automatic transmission image capture, and calculates accurate displacement. The displacement distribution is uniform in linear elastic stage, and varies in yielding stage. This is mostly due to localized failure and displacement discontinuity.