PSI - Issue 42

T. Koščo et al. / Procedia Structural Integrity 42 (2022) 1600 – 1606

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Koščo, T., Chmelko, V. / Structural Integrity Procedia 00 (2019) 000 – 000

neighbourhood. After deeper research, authors consider it natural, that the filter doesn’t play the most significant role due to the nature of the displacement field. In case of larger region of interest, filtering parameters would probably play the most significant role and the effect of large variance would decrease. The result is influenced by the superposition of all these effects. Therefore, the authors have been looking for a range of sizes with minimum influence of mentioned effects. On Fig. 7 can be seen, that notch sizes above 100 pixels per notch radius result relatively good results, for both horizontal and vertical configuration as well. Satisfactory results have been obtained above 150 pixels per radius with standard deviation of the result less than 4*10 -5 . These results have been obtained with a speckle pattern with MIG parameter of the speckle pattern larger than 20. Authors consider the results as usable for generally shaped notch with rapid strain gradient in one direction.

Fig. 6. Deterioration of hysteresis loops for multiple measurement for different notch sizes

5. Measurement on welded specimen Knowledge gained from previous measurements have been utilized by a measurement on generally notched, welded specimen (see Fig. 7a). 4mm thick specimen was cut out of a gas pipeline from X52 steel. Welded pipes do not have same thickness. Therefore, the thicker one is determined as a reference. After tensile loading, reference stress in the thicker part of the specimen has been 110 MPa. One of the most stressed points (shown by the arrow on Fig. 7b) is caused by a relatively shallow notch with relatively large radius. Results in this point report minimal filter dependence. Resulting strain field in the critical point changes rapidly only in one direction, what indicates a possibility of use of previously mentioned data. At this point it must be mentioned that the pixel per radius value of a random notch geometry on welded joint cannot be estimated accurately. One of possible

Fig. 7. (a) welded specimen (b) measured strain field