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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the three-dimensional space (Fig. 1). The strain fields were projections of these local surface areas.

Fig. 1. The image registration scheme from a speckle pattern of the butt-welded joint under the tensile load: K1 and K2 are digital cameras; P is the applied load 3. Results and Discussion Stress-strain curves  (  ) were drawn for both samples under applied loads (Fig. 2). Micro-plasticity (and deviation from Hooke's law) began at a stress of 0.35% according to the steel sample stress-strain curve (Fig. 2, c). It was expressed both in the bending curve  (  ) and in a qualitative change in the distribution patterns of the strain fields on the sample surface (Fig. 3, patterns 1 and 2) that reflected the effects of the macroscopic localization of inelastic strains at the elastoplastic stage. At the next stage, the macro-uniform distribution of the strain fields transformed into an inhomogeneous one as a result of the combining randomly located individual spots of inelastic strains into large areas.

Fig. 2. The stress-strain curves of the steel (a) and welded (b) samples: points 1, 2, 3, …, 8 indicate states on the stress–strain curves correlated with the distribution patterns of stain fields shown in Figures 3 and 4; c and d are magnified parts of the stress-strain curves at the initial loading stage; Т , II, III, IV are the stages on the stress-strain curves