PSI - Issue 30

Kirill Kurgan et al. / Procedia Structural Integrity 30 (2020) 53–58 Kirill Kurgan et al. / Structural Integrity Procedia 00 (2020) 000–000

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enable to predicting their reliability. The process of deformation of metal in welds is rather complicated due to the presence of residual stresses as stated by Macherauch and Wohlfahrt (1977). Therefore, experimental methods for studying the material behavior in the welded joints under loads play an important role. The advanced method -for measuring strain fields based on a optical system ‘Vic-3D’ enables to obtain data on the displacement of points on a sample surface under the action of tensile loads as stated by Sutton et al. (2009). Austenitic stainless steels are widely used in various industries as a structural material. In addition to high corrosion resistance in aggressive environments, they possess high strength properties, such as high impact toughness and ductility, as well as good weldability. For this reason, they are used in the manufacture of welded structures for various applications including cryogenic equipment, steam heaters, high pressure pipelines, etc. The 0.12%C-18%Cr-10%Ni-1%Ti steel is one of the most sought-after austenitic grades. Today a lot of investigations of its welded joints have been carried out, for example by Fu et al. (2015). In situ studies of the dynamics of the strain fields in the welded joints based on the implementation of non-contact three-dimensional digital optical systems are one of the most advanced methods according to Tretyakova and Wildemann (2019). This paper is next step in expanding knowledge using the mentioned capabilities of the up-to-date research equipment. Its goal was to study the dynamics of deformation fields both in a plate made of austenitic stainless steel 0.12%C-18%Cr-10%Ni-1%Ti and in its butt-welded joint under tensile loads.

Nomenclature Р

applied load digital cameras

K1, K2  X, Y, Z U, V, W

strain-induced phase transformations

Cartesian coordinates movements at each point

ε xx , ε yy , ε xy

components of relative deformation

 (  )

stress-strain curve

2. Materials and methods The investigations were carried out on two samples. The first was a plate with dimensions of 70  15  1.5 mm from the austenitic stainless steel 0.12%C-18%Cr-10%Ni-1%Ti (Table 1, hereinafter referred to as steel). A second welded sample was obtained by butt-joining two steel plates using gas tungsten arc welding.

Table 1. The chemical composition of the studied austenitic stainless steel Element Cr Ni Ti

Si

Mn

Cu 0.3

S

P

Fe

Composition, % wt.  68 The samples were stretched using an ‘INSTRON 3386’ electromechanical testing machine with a constant rate of 0.3 mm per minute. The strains were measured using a ‘Vic-3D’ optical system, which made it possible to obtain data on the displacements of points on the sample surfac during its extension according to Tretyakova and Zubova (2018). They were recorded on the basis of an extensometer installed at the studied samples from the upper clamp of the testing machine to the lower one, as well as at the weld surface (Fig. 1). The image analysis of the investigated surfaces was carried out after the formation of a speckle structure on it, i.e. irregular drawing of many points on a contrasting background. During the test, the ‘VicSnap’ software recorded images from two cameras simultaneously. The stereo images were processed by the ‘Vic-3D’ software, that calculated the displacements of the surface points in three mutually perpendicular axes by applying the digital image correlation method. The output data were the X, Y, and Z coordinates for each analyzed point; the movements U, V, and W at each point along the X, Y, and Z axes, respectively; as well as strains (transverse strains ε xx along the X axis, longitudinal strains ε yy along the Y axis, and tangential strains ε xy ). As a result, an array was obtained on the displacement of the surface metal microvolumes in 18 10 0.8 0.8 2 0.02 0.035