Digital Speckle Correlation Method Research Articles

Experimental analysis of crack tip fields in rubber materials under large deformation

A three-nested-deformation model is proposed to describe crack-tip fields in rubber-like materials with large deformation. The model is inspired by the distribution of the measured in-plane and out-of-plane deformation. The inplane displacement of crack-tip fields under both Mode I and mixed-mode (Mode I–II) fracture conditions is measured by using the digital Moire method. The deformation characteristics and experimental sector division mode are investigated by comparing the measured displacement fields under different fracture modes. The out-of-plane displacement field near the crack tip is measured using the three-dimensional digital speckle correlation method.

Experimental investigation on deformation and strength of carbon/epoxy laminated curved beams

Both the deformation and strength of carbon/epoxy laminated curved beams with variable curvature and thickness are studied experimentally using the Digital Speckle Correlation Method (DSCM) and a Four-Point-Bending test configuration. First, the relationships between the strain and the applied load on the curved beams with different thicknesses and different radius-thickness ratios are studied. Second, both the failure strength and the maximum interlaminar radial stresses of the curved beams are determined, and the distribution and evolution of full field strain in the laminated curved beams are obtained using DSCM. Finally, the interlaminar deformation and delamination mechanisms of carbon/epoxy laminated curved beams are analyzed. These results play an important role for predicting strength and evaluating lifetime of laminated curved beams.

The Experimental about the Weak Surface Slop Deformation and Failure under Earthquake Effect

In order to study the law of containing the weak surface slope deformation and failure under earthquake action simulate under earthquake action deformation and failure of the model which is a single weak surface slope. Use the digital speckle correlation method to deal with the experimental results, and obtain displacement and strain of the slope model. From the experimental results: it can be found the displacement and strain are concentrated in the weak surface , with the continuous vibration, eventually leading to the slope failure. The model crack firstly appears in the top of the experiment picture, and extends downward along the weak surface, thus lead to the model slip.By the experiment picture analyze the causes of the cracks.

用数字散斑法测量铜/铝复层板拉伸变形

To measure the deformation of copper/aluminum clad metals made by explosive welding technique,a new full-field three-dimensional deformation measurement method based on the digital speckle correlation method and binocular stereovision was proposed and implemented.The related key technologies including image correlation matching,three-dimensional coordinates,displacement and strain reconstruction were investigated.Then a deformation measurement system and corresponding software were developed based on the VC++6.0 platform.To validate the feasibility of the proposed method,a precision test and a copper/aluminum clad tensile test were conducted,and the experimental data of the test and the numerical simulation using Abaqus software were compared.Experimental results show that the accuracy of strain measurement is not lower than 0.5%,very close to that of the extensometer.The extreme strain distribution based on digital speckle correlation method is coincident with that the finite element simulation well.Furthermore,the simulated curves of plastic stress-strain are in agreement with the experimental data before necking the sheet metal,and the tendency of simulated curves of displacement-load is consistent with the experimental data in the whole tensile processes.Moreover,the relative errors of simulated ultimate load are from 0.06% to 2.25%.It demonstrates that the digital speckle correlation method is an effective tool to obtain the full-field strain of sheets accurately.

基于数字相关法的应力应变检测技术及应用

The stress states are measured for hot wind furnace of balst in working and reliable data are supplied for safety operation.Dispalcements and strains of shell of hot wind furnace are measured by digital speckle correlation method(DSCM) in real time.Simultaneously,mark point method is also adopted for measuring the displacements and strains of hot wind furnace shell in order to compare the results obtained by DSCM.In the experiment,displacements and strains of circular and axial direction for furnace shell are obtained successfully.And the results obtained by DSCM and mark point method agree well.Through on-the-spot test,it can be concluded that the working stresses are lower than permissible stresses under different working states for hot wind furnace.So the operation of the hot wind furnace is safety.

Experimental Study on the Influences of Deffctive Concrete on Chloridion Penetration Resistance

Micro-crack defects in concrete can affect the Chloride ion permeability of concrete in a certain extent. In the paper, the splitting experiments of concrete specimens from the four different dimensions are carried out in order to build the even damage fields. The displacements of the concrete specimens’ surface are analyzed through DSCM (Digital Speckle Correlation Method). Therefore damage parameters are determined that are damage area based on the MCOD (Micro-Crack Opening Displacement) and damage variable DE based on the weighting-damping elastic modulus. At the same time, Clˉ permeation of concrete specimens before and after the splitting test are studied by NEL method, and Clˉ diffusion coefficients D are recorded in detail. Further relationships between damage parameters and diffusion coefficients of Clˉ are discussed.

Application of Digital Speckle Correction Method to Inverted Camber Detection of Prestressed Foundation Beam

Based on the principle of digital speckle correlation method (DSCM), a distance measuring DSCM system has been developed and realized. With the application of the system, the inverted camber of a pre-stressed beam of beam-slab transfer cadre was traced and analyzed in this paper. Compared with other experimental technique such as dial indicator test method, it shows that DSCM is a powerful optical deformation measurement tool with the required precision and on-site inspection ability.

A Novel 3-D Testing System for the Mechanical Properties of Fiber Fabrics and Textile Composites

To evaluate the mechanical properties of natural fiber fabrics with the characteristic of interweaving between warp and weft direction as well as textile structural composites under complex stress state, it is essential to develop experimental techniques to realize multi-axial testing for large deformation. This work proposes a novel testing device for investigating fiber fabrics and textile composites under multidimensional loads. Accuracy of the system is comparable to the testing diagnostics of the Instron 5808 previously. The homogeneity for different types of cruciforms and different biaxial tensile speeds were investigated. The effects of different loading methods, biaxial (X and Y), and 3-D loading (X, Y, and Z) on the breaking strength of the woven ramie fabric were presented. The displacement-field and shear field for composites with hole were characterized by the digital speckle correlation method.

Application of model photomechanics technique in biomedicine and engineering

The theories of digital speckle correlation method, shadow moire method, photoelestic method,moire interferometry method and electronic speckle interferometry method were introduced. The applications of these modern photomechanics methods in biomedical engineering from both domestic and abroad were introduced, respectively. This review will provide inspiring methods and experimental technique for biomedical engineering research and promote profound exploration.in the field. Key words: Optical measuring technology; Biomedicine engineering; Displcement fields; Stress fields

Study on mixed‐mode fracture characterization in functionally graded materials

AbstractThe fracture characterizations on mixed‐mode crack of functionally graded materials (FGMs) are investigated using digital speckle correlation method (DSCM). The stress intensity factors at mixed‐mode crack tip are obtained from digital speckle displacements fields. In combination with finite elements simulation results, the influences of gradient coefficients on fracture behavior of mixed‐mode cracks are analyzed. All the results show that the influence of gradient coefficients on fracture modes is not noticeable, and the stress intensity factor at the crack tip in graded materials are clearly influenced by the gradient coefficients, i.e., the stress intensity factors decrease with the increasing of gradient coefficients. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Deformation-pattern-based digital speckle correlation for coefficient of thermal expansion evaluation of film

In this paper, a digital speckle correlation method for coefficient of thermal expansion (CTE) measurement of film is developed, in which CTE is the intrinsic parameter and direct variable. Deformation pattern governed by the CTE and temperature is used to affine transform the image captured after the film is heated. If the values of CTE are properly chosen, the image after affine transformation will have a highest similarity to the original image. This turns CTE measurement into a purely numerical search of an optimal trial CTE. Results of CTEs from this method and conventional DIC methods are compared with the actual CTE, showing an improved accuracy.

Automatic Measurement of Concrete Deformation Field under Uniaxial Compression Based on DSCM

As a kind of optical approach to measure full field deformation with the properties of non-contact, Digital Speckle Correlation Method (DSCM) has been adopted widely with the development of computer technology. The deformation of concrete under external loads is usually uneven and thus it should be characterized by full filed measurement so as to obtain accurate results. It should be effective for engineering to monitor the deformation of concrete by using digital speckle correlation method, and such monitoring is helpful to study the law of uneven deformation of concrete and discover its damage characteristics. The images of the surface of concrete specimens at the different stress were captured and recorded with a high-resolution CCD camera during uniaxial compression process. An own software was developed to analyze these images by DSCM. The nature texture of the specimen surface were searched and matched in different images, therefore the displacement field and the strain field of the surface of concrete specimens were calculated out. Experimental studies have shown that digital speckle correlation method can be well used to calculate the accurate deformation of concrete just through a direct photograph of concrete surface under different loads.

Measuring Stress Distributions of Orthotropic Composite Material in Plane Stress State by the Lock-in Infrared Thermography Technique

Feasibility of measuring stress distributions of orthotropic composite materials and structures in plane stress state by the lock-in infrared thermography technique is analyzed and stress distributions of a lap joint structure made of a kind of glass reinforced plastic composite lamination plates under tensile loadings are obtained by the lock-in infrared thermography technique. Feasibility and credibility of using this technique to measure stress distributions of orthotropic composite materials and structures in plane stress state are proved by comparing the results with the data given by the digital speckle correlation method.

Interactive effect between warp and weft of a woven ramie fabric under biaxial loadings

The occurrence of an interactive effect between warp and weft of woven fabrics under practical working conditions is an important concern for researchers. A novel 3D loading device has therefore been developed to elucidate information on materials subjected to loadings in multiple dimensions. This paper investigated the interactive effects between warp and weft in biaxial tension. Strain fields were characterized by digital speckle correlation method and Poisson’s ratio was calculated at 0° in the warp direction. The effects of different cutting angles and loading threshold values at 0° on the interactive effect were also evaluated. An interactive effect between warp and weft existed, and the influence of load at weft to warp was larger than warp to weft. Weft produced larger strain fields in both directions. As the load in the warp direction linearly increased, force values nonlinearly increased while load ratio decreased. Poisson’s ratio, however, was practically unchanged. Loading mean value curves at x and y axes had sine curve characteristics. The greatest interactive effect occurred when the warp load was 65.3% of the biaxial breaking strength.

A modified layer-removal method for residual stress measurement in electrodeposited nickel films

Combining the traditional layer-removal method with a cantilever beam model, a modified layer-removal method is developed and used to measure residual stress in single and multi-layer electrodeposited nickel films with thickness of 2.5 μm. The out-of-plane displacement of the free tip of a cantilever beam is measured by the digital speckle correlation method. The results show that residual stress in a single semimat nickel film is compressive, while in a multi-layer system composed of dark, semimat and holophote nickel, residual stress in the surface layer is tensile. Residual stress decreases gradually with the increase of etching depths of single and multi-layer films. These findings are in qualitative agreement with nanoindentation tests, which confirms the reliability of the modified layer-removal method.

基于数字散斑的弯管残余应力测量系统的误差分析

基于数字散斑的弯管残余应力测量系统的误差分析

The Experimental Study on Fracture Process of Similar Rock Material with Different Ductility

The surface strain fields evolutions of three specimens similar to the rock material subjected to uniaxial compression, which are observed by digital speckle correlation method, are analyzed. The five typical moments of the sample destruction are selected for analysis. The shear strain fields at typical loading levels corresponding to the five typical moments are presented. The characteristics of the deformation fields are concluded. It is found that strain localization occurs earlier and becomes complicated, and the angle between the rupture surface and loading direction are bigger. The failure mode of specimen changes from macro- crack to the multiple crack, when ductility of specimens increases. Experimental results show that failure process and failure law of the similar material of rocks are quite different because of different toughness. So, different models need to be selected to obtain more realistic in numerical analysis.

Experimental investigation of interface curing stresses between PMMA and composite using digital speckle correlation method

This paper studies the interface curing stresses between polymethyl methacrylate (PMMA) and composite by means of digital speckle correlation method (DSCM). A new method by combining DSCM with the marker points is developed to measure the interface curing stresses, and the measurement principle is introduced. The interface curing stresses between PMMA and composite with different curing bonding conditions are measured and analyzed, this indicates that the residual stress for furnace heating and furnace cooling is the smallest. Finally, the measurement error is discussed by means of finite element method, the influences of glass microsphere between adhesive and PMMA can be ignored.

Experimental analysis of crack tip fields in rubber materials by 3D Digital Image Method

This paper presents the application of 3d digital image method to determine the crack tip fields in rubber materials. The in-plane displacement of crack-tip fields under Mode I loading is measured by using the digital moiré method and the out-of-plane displacement field near the crack tip is measured using the three-dimensional digital speckle correlation method. Basis on the in-plane and out-of-plane deformation distributions, a three-nested-deformation model is proposed to describe crack-tip fields in rubber-like materials with large deformation.

数字散斑相关法在变形测量中的应用

数字散斑相关法在变形测量中的应用