Evaluation of local constitutive properties of Al2024 friction stir-welded joints using digital image correlation method

2020 ◽  
pp. 030932472098120
Author(s):  
A. Shahmirzaloo ◽  
M. Farahani ◽  
M. Farhang
Keyword(s):  
Mechanical Properties ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Welded Joints ◽  
Local Stress ◽  
Image Correlation ◽  
Welding Parameters ◽  
Stress Strain ◽  
Friction Stir ◽  
Dic Technique

The intense applied thermal gradients during the welding process leads to the variation in the properties of the weld zone and its surrounding areas. In this regard, determining the local mechanical properties and evolved microstructures of the weld and its surrounding zones are essential in the evaluation of welded structures. In this study, the local mechanical properties of Al2024 friction-stir-welded joints were precisely examined. Digital image correlation (DIC) technique using uniform stress (USM) and virtual field methods (VFM) were utilized to evaluate the local mechanical properties. The local stress-strain curves were plotted for different weld regions using local strain from the DIC technique. It was observed that the advancing side of the thermo-mechanically affected zone (TMAZ) had the lowest values of Young’s modulus and yield strength (YS), approximately 9% and 31% of the base metal, respectively. Effects of welding parameters, such as tool rotational and traverse speeds, were also taken into account. The plotted local stress-strain curve for the fractured region of welded specimens at lower rotational speed illustrated a higher strength and elongation. Furthermore, lower rotational and also higher traverse speeds resulted in the reduction of the grain size.

Local Elasto-Plastic Identification of the Behaviour of Friction Stir Welds with the Virtual Fields Method

2011 ◽  
Vol 70 ◽  
pp. 135-140 ◽  
Author(s):  
G. Le Louëdec ◽  
M.A. Sutton ◽  
Fabrice Pierron
Keyword(s):  
Mechanical Properties ◽  
Digital Image Correlation ◽  
Digital Image ◽  
High Speed ◽  
Weld Zone ◽  
Spatial Variations ◽  
Image Correlation ◽  
Virtual Fields Method ◽  
Full Field ◽  
Friction Stir

Welding is one of the most popular joining technologies in industry. Depending on the materials to be joined, the geometry of the parts and the number of parts to be joined, there is a wide variety of methods that can be used. These joining techniques share a common feature: the material in the weld zone experiences different thermo-mechanical history, resulting in significant variations in material microstructure and spatial heterogeneity in mechanical properties. To optimize the joining process, or to refine the design of welded structures, it is necessary to identify the local mechanical properties within the different regions of the weld. The development of full-field kinematic measurements (digital image correlation, speckle interferometry, etc.) helps to shed a new light on this problem. The large amount of experimental information attained with these methods makes it possible to visualize the spatial distribution of strain on the specimen surface. Full-field kinematic measurements provide more information regarding the spatial variations in material behaviour. As a consequence, it is now possible to quantify the spatial variations in mechanical properties within the weld region through a properly constructed inverse analysis procedure. High speed tensile tests have been performed on FSW aluminium welds. The test was performed on an MTS machine at a cross-head speed of up to 76 mm/s. Displacement fields were measured across the specimen by coupling digital image correlation with a high-speed camera (Phantom V7.1) taking 1000 frames per second. Then, through the use of the virtual fields method it is possible to retrieve the mechanical parameters of the different areas of the weld from the strain field and the loading. The elastic parameters (Young’s modulus and Poisson’s ratio) are supposed to be constant through the weld. Their identification was carried out using the virtual fields method in elasticity using the data of the early stage of the experiment. Assuming that the mechanical properties (elastic and plastic) of the weld are constant through the thickness, the plastic parameters were identified on small sections through the specimen, using a simple linear hardening model. This method leads to a discrete identification of the evolution of the mechanical properties through the weld. It allows the understanding of the slight variations of yield stress and hardening due to the complexity of the welding process.

Local Stress-Strain Response of an Axial X100 Girth Weld Under Tensile Loading Using Digital Image Correlation

2006 ◽  
Author(s):  
Samer Adeeb ◽  
Dave Horsley ◽  
Junhui Yan ◽  
Michael A. Sutton ◽  
Anthony P. Reynolds
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Thermal Cycle ◽  
Strain Aging ◽  
Welding Process ◽  
Tensile Tests ◽  
Image Correlation ◽  
Strain Response ◽  
Stress Strain ◽  
Dic Technique

An important design, construction and maintenance concern for pipelines is the integrity of flaws in the girth welds. Numerous fitness for purpose codes are available to assess weld flaws, many of which were calibrated with reference to wide plate test data. Often, wide plate tests are conducted on girth welded pipe in the as-received condition, i.e. without application of a pipeline coating. The area adjacent to the weld is thus subjected to a thermal cycle due to the heat generated from the welding process. In some pipe materials this thermal cycle might be sufficient to induce strain aging. It is not clear how the welding process changes the behaviour of the area next to the weld. The results of such wide plate experiments are very important in assessing the acceptable flaws in a girth weld under a strain-based design. Therefore, it was important to understand the extent of the aging, specifically the stress-strain behaviour on either side of the girth weld. This paper presents results of cross-weld tensile tests, which utilized a two-dimensional digital image correlation (DIC) technique to determine displacement, and thus infer strain. The local strains were mapped to global stress to obtain local constitutive properties every 12.5mm along the length of the specimen. The DIC test results were very consistent and were also similar to results obtained from standard circumferential tensile tests at corresponding locations. The strength of the specimens, as defined by the relative strength of their stress-strain curves, was found to be highest in the girth weld region, to drop in the HAZ, and then to reach a plateau in the base metal. It was also shown that strain localization in one of the HAZ regions was clearly visible during the loading process and the near-HAZ regions had a stress-strain response with a yield stress value higher than the base metal. This behaviour was observed at 12.5mm away from the girth-weld centerline in both the transverse and longitudinal directions. The reason for this slight change of behaviour can be attributed to the effect of heating supplied to this part during welding (strain aging). The described DIC technique is very promising in obtaining local strain fields within very small areas of the tested specimens.

scholarly journals Exploring digital image correlation technique for the analysis of the tensile properties of all-cellulose composites

Cellulose ◽  
2021 ◽  
Vol 28 (7) ◽  
pp. 4165-4178
Author(s):  
Feng Chen ◽  
Jean-Luc Bouvard ◽  
Daisuke Sawada ◽  
Christophe Pradille ◽  
Michael Hummel ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Tensile Properties ◽  
Young’S Modulus ◽  
Digital Image ◽  
Young's Modulus ◽  
Image Correlation ◽  
Correlation Technique ◽  
Stress Strain ◽  
Cellulose Composites ◽  
Dic Technique

Abstract All-cellulose composites (ACCs) were prepared from filter paper via partial dissolution in the ionic liquid 1-ethyl-3-methylimidazolium acetate, and material tensile properties were investigated using various approaches. One is based on data directly taken from a tensile testing machine, and the other uses two-cameras stereovision with digital image correlation (DIC) technique. In the latter case, virtual extensometer with different locations on the sample and averaging over sample surface were tested. Nominal and true stress–strain dependences were built and Young's modulus, tensile strength, elongation at maximal stress and toughness were evaluated as a function of ACC density. A minor difference was observed for the stress–strain dependences derived from different approaches which use the DIC technique, most probably because of low ACC deformation. However, the results reveal that the nominal stress–strain curve from DIC is significantly different from that which is directly derived from the data provided by machine sensors thus strongly impacting Young’s modulus and elongation at break values. This study provides an insight into the evaluation of the mechanical properties of ACCs. Graphic abstract

Full-Field Strain Behavior of Friction Stir-Welded Titanium Alloy by Digital Image Correlation

2014 ◽  
Vol 692 ◽  
pp. 490-496 ◽  
Author(s):  
Mamidala Ramulu ◽  
Trent Greenwell ◽  
Paul Labossiere
Keyword(s):  
Titanium Alloy ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Thin Sheet ◽  
Measurement Techniques ◽  
Image Correlation ◽  
Stress Strain ◽  
Full Field ◽  
Friction Stir ◽  
Strain Behavior

Experimental investigation is conducted to examine, evaluate, and characterize the fundamental elastic-plastic stress/strain response of friction stir-welded butt joints in thin-sheet, fine grain Ti-6Al-4V titanium alloy under normal tensile loading using traditional global stress-strain tensile testing and the full-field displacement measurement techniques of Digital Image Correlation (DIC). It was found that overall strength of friction stir-welded Ti-6Al-4V is comparable to the accepted values for mill-annealed Ti-6Al-4Valloy. Overall strain performance of friction stir-welded Ti-6Al-4V is roughly half that of the accepted values for pure mill-annealed Ti-6Al-4V. In addition, friction stir-welded Ti-6Al-4V demonstrates a consistent pattern of strain localization between the onset of yielding and ultimate failure.

Measurement of tensile mechanical properties of fiber reinforced plastic rebars by 3D digital image correlation

2020 ◽  
Vol 62 (4) ◽  
pp. 422-428
Author(s):  
Feipeng Zhu ◽  
Pengxiang Bai ◽  
Dong Lei
Keyword(s):  
Mechanical Properties ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Curved Surfaces ◽  
Fiber Reinforced ◽  
Stress Strain ◽  
Fiber Reinforced Plastic ◽  
Reinforced Plastic

Abstract Fiber reinforced plastic (FRP) plays an increasingly important role in many engineering fields due to its advantages of light weight, low cost, simple maintenance, and excellent corrosion resistance. The conventional contact methods for deformation measurement, such as strain gauge and mechanical extensometer, have some shortcomings in measuring the strain of FRP rebar specimens with spiral curved surfaces. Therefore, the non-contact three-dimensional digital image correlation (3D-DIC) technique was employed to determine the tensile mechanical properties of two types of FRP rebar specimens, i. e. glass FRP (GFRP) and carbon FRP (CFRP) specimens. Uniaxial tensile tests with three different loading rates were conducted to obtain the stress-strain curves, elastic modulus, tensile strength and percentage total extension at maximum force of these two FRP specimens. Experimental results indicate that the axial-strain field of all FRP rebar specimens present nonuniform distribution and that the stress of GFRP and CFRP rebars varies linearly with the strain. Moreover, no yielding phenomenon was observed from the stress-strain curves, which indicates that both GFRP and CFRP rebars belong to the group of typical brittle materials. The dispersion of elastic moduli obtained using 3D-DIC is better than that using a clip-on extensometer, which demonstrates the validity of 3D-DIC for the determination of tensile mechanical properties of FRP rebars with spiral curved surfaces.

Determination of Weld Metal Mechanical Properties Utilising Novel Tensile Testing Methods

2007 ◽  
Vol 7-8 ◽  
pp. 127-132 ◽  
Author(s):  
M. Kartal ◽  
Rafal M. Molak ◽  
Mark Turski ◽  
S. Gungor ◽  
Michael E. Fitzpatrick ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Weld Metal ◽  
Tensile Test ◽  
Weld Zone ◽  
Local Stress ◽  
Gauge Length ◽  
Image Correlation ◽  
Stress Strain ◽  
Strain Behaviour ◽  
Dic Technique

The aim of this study was to develop a method of extracting local mechanical properties from weld metal by strain mapping using the digital image correlation (DIC) technique. The feasibility of determining local stress-strain behaviour in the weld zone of a 316H stainless steel pipe with a girth weld was investigated by tensile tests of specimens machined from the pipe so that it contained the weld at its centre. The tensile test was recorded using a high resolution digital camera and the DIC technique was used to obtain the complete set of full field displacement maps during the tensile test. The local strain was calculated at every sub-region of 32×32 pixels, which enabled the local stress-strain behaviour for this region to be determined. Results from these tests show the variability of the elastic modulus, yield stress and UTS across the weld. To check the reliability of the technique, a set of micro tensile samples, with gauge length of 3.7mm and crosssectional area of 0.7×0.7 mm2, were machined from the various locations in and around the weld zone. The comparison of stress-strain curves determined from micro-samples to stress-strain curves from the corresponding locations within a larger more conventional tensile specimen shows reasonably good agreement.

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