Comparison between Digital Image Correlation and Thermoelasticity for Strain Field Analysis (original) (raw)
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Surface Deformation or displacement of any material and structure at a macro, micro or nano level because of the external effect (both mechanical and thermal) is the point where failure of the material is initiated. To know why and how materials are failed many researchers and engineers have been conducted different investigation on the field of mechanics of materials. Specially, knowing the value and behaviour of displacement, strain, and stresses induced in any loaded members and structure is the crucial way to reduce the failure of material. For this reason, many researchers have been conducted numerous investigation which modifies, and improves an accuracy and computational time of the DIC. Nowadays, digital image correlation (DIC) is a technique which gained immense attention on the field of experimental mechanics due to its versatility measurement accuracy including strain measurement. DIC is a full field, non-contact, optical, strain and displacement measurement technique; it is simple, cost effective and high accuracy as compared with the other strain measurement technique.
2017
Determining the strain flow and stress distribution in metallic materials during their deformation represents a significant challenge for researchers. The foil strain gage gave the possibility to test the actual stress in the deformation zone. Their application at higher deformations has proven to be limited, and does not give information on the entire deformation zone. With the development of digital technology, methods of digital image correlation (DIC) and thermography were developed. Their applications in researches today are more frequent, and are commonly being used for studying deformation of metals. The aim of this study was to determine the possibility of applying DIC method parallel with thermography to monitor the stresses distribution in deformation zone during the static tensile testing. The possibility of measuring with both methods on the same side of the sample, and the impact of markers required for DIC on the thermographic measurements, were tested. It has been pro...
Strain analysis at flat surfaces of loaded members using digital image correlation technique
Periodicals of Engineering and Natural Sciences (PEN), 2020
This research examines the applicability of the planned Digital Image Correlation (DIC) system to measure the strains in tensile experiments. DIC is a low-cost optical technique, and is an appropriate measurement used to measure surface displacement, strain and stress map distribution without any contact with the tested surfaces. In the present research, the tensile test is conducted on two different flat samples, which are painted in a speckle pattern on the tested surface to use DIC features in stain measurements. To guarantee the efficiency of the planned DIC system, the DIC code has been built using MATLAB programming language. The obtained results from DIC technique is compared with the results from open-source software (Ncorr), the finite element analysis (ANSYS) as well as the exact and analytical solutions. The comparison results showed that there was A quite acceptable and agreement achieved between them. According to the exact solution, the percentage of accuracy of the obtained results for the Aluminum without hole plate was around (89-93) % whereas the accuracy with the NCORR was about 96 %. For the second copper plate with a central hole, the accuracy has been obtained to be (80.7-99) % with the analytical solution wherein its value has reached (81-97) % with Ncorr software.
Polymer Testing, 2009
This paper presents an experimental investigation of the mechanical behaviour of a talc and elastomer modified polypropylene compound subjected to large strains. 3D digital image correlation with two cameras and stereo-vision was used to determine full-field displacements during uniaxial tensile tests on specimens with rectangular cross-section. Local strains were derived from the displacement field and used to calculate the current cross-sectional area of the specimen during the whole loading process. Points on the true stress-strain curve (Cauchy stress versus logarithmic strain) were then calculated from the data. Volume dilatation was separated into elastic and plastic parts through tests where the specimens were unloaded after varying degree of stretching. The unloading events were also used to investigate damage evolution as function of plastic straining.
Mechanics & Industry, 2017
The deformation and strain measurements have always been one of the main issues in structural engineering. Measuring displacements accurately without damaging structures are an important aim in experimental analysis. For an example, the existing structures need to be evaluated whether they are still fit for purposes or not. To assess complex structures, we need an acceptable and enough amount of data Current strain measurement technologies are not capable of evaluating compounded structures. This paper investigates on an alternative method that uses digital images to provide a full displacement and strain field called Digital Image Correlation (DIC); This technique compares the digital images taken from digital cameras, before and after deformation. We also calculated the coefficient of plastic anisotropy. An aluminium 1050 specimen was loaded in tension according to ASTM E8 testing method while the Sony camcorder captured the video of the specimen being loaded. Once the video was captured, the images were snapshot from video strip using a built-in function of the camera. After that, the images were processed using the Matlab software. The results determined by the extensometer and the optical strain measurement method were compared to each other. This comparison shows that if the test's setup could be configured in a good way, the error will be less than 2%.
The power of Digital Image Correlation for detailed elastic-plastic strain measurements
Digital image correlation is more and more applied in test environments where material behavior is investigated. The advantages of using images for analyzing the deformations in a specimen are enumerable. Besides making it easier to perform some tests, digital image correlation enables it to make detailed material behavior visible which previously could only be shown by modeling. At Delft University of Technology, a tool was developed to use digital image correlation for tensile tests on weld. However, within a short period of time different test applications were found for which the digital image correlation tool could be used. This paper describes the details of the digital image correlation tool and some examples in which the tool was applied in different test.
Digital Image Correlation Technique in Selected Mechanical Tests
2017
The paper shows how modern contactless Digital Image Correlation (DIC) method can be implemented for examination of material behaviour under various types of loading. DIC method was used to evaluate material straining under monotonic tension conducted by the use of flat specimens having artificial defects in the form of U and V notches. This technique was also examined during capturing of strain distribution in dynamic tests on Split Hopkinson Pressure Bar. On the basis of DIC results the strain maps at various stages of material deformation were elaborated in order to indicate characteristic features of a material behaviour. It enabled an analysis of damage zone evolution up to specimen fracture.
The Journal of Strain Analysis for Engineering Design
This article discusses the dual use of digital image correlation and thermoelastic stress analyses for the study of propagating cracks. It is shown that a few critical parameters such as emissivity and the thermoelastic constant required for the latter can be calibrated with the former. A unified framework is introduced, which treats both experimental techniques equally to locate crack tips, and then evaluate stress intensity factors. This framework allows for a detailed and quantitative comparison between both methods. It is found that, for the case at hand, the thermoelastic stress analyses outputs were less noise sensitive while the digital image correlation method was less dependent on calibration. The proposed procedure was very robust for finding the crack tip location for both experimental methods.
Digital Image Correlation in Experimental Mechanical Analysis
2012
Digital image correlation (DIC) is a powerful noncontact technique for measuring surface displacement/ strain fields. Some of the methods, focused on 2D analysis, are used for determining mechanical properties of specimens of simple geometric shape. More advanced 3D analysis can be used not only for specimens, but also for real objects of complex geometric shapes. Application of DIC technique in experimental mechanical analysis using software Aramis for 3D displacement/strain measurement is presented in this paper. Ključne reči • korelacija digitalne slike • mehanička analiza • Aramis softver
Application of Digital Image Correlation in Uniaxial Tensile Test
2016
Application fields of non-contact measurement techniques have been recently increasing by means of optics and technological development in measurement applications. Digital image correlation (DIC) is the one and powerful non-contact measurement method that can be used to obtain elongation and strain as well. It is versatile and flexible measurement method can be adopted to many traditional test experiments such as tensile, compression, and bending in order to calculate mechanical properties of materials. In this study, DP600, DP800 and DP980 steel materials were performed to uniaxial tensile test and DIC technique was used to determine local strains in terms of comparison in different regions at the fracture area. While performing experiments, commercial DSLR camera was installed to capture videos under the white led lighting which is needed to decrease visual blurring and keep contrast as constant. Recorded videos were analyzed with VIC-2D software in an effort to calculate strain ...