PSI - Issue 42

Halyna Krechkovska et al. / Procedia Structural Integrity 42 (2022) 1406–1413 Halyna Krechkovska / Structural Integrity Procedia 00 (2022) 000 – 000

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probability of their non-destruction was reached. At stresses close to the conditional fatigue limit, composition rods did not break down even with test base of 5∙10 7 cycles. Only sometimes longitudinal cracks were observed on their surface, which were interpreted as a consequence of the formation of delaminations in the surface layer of the composite reinforced with glass fibers, due to the action of cyclic loads. It can be even expect an higher efficiency of using hybrid rods made of fiberglass composites in the oil production process. After all, the fatigue life of sucker rods in an oil emulsion is 15…25% higher than when they are operated in formation salt water (Fig. 7), Kopey 4 et al. (2020).

160

2

120

1

80

s , MPa

3

40

0

10 4

10 5

10 6

10 7

N , cycles

Fig. 7. Fatigue life curves σ – N of fiberglass (1), hybrid (2) and steel sucker rods (3).

The fatigue curves σ – N obtained during the test for cantilever bending of samples from composite (reinforced with glass fibers), hybrid and steel sucker rods were compared with each other (Fig. 7). With a test base of 2˕10 7 cycles, hybrid sucker rods with a carbon fiber reinforced core and a glass fiber reinforced shell have the highest level of conditional fatigue limit (Kopei (2019 2 , 2021 3 ). Conclusions Analysis of the fatigue life of sucker rods with a diameter of 19 and 22 mm made of 20N2M steel showed that the rods with operational defects had a significantly lower resistance to fatigue failure compared to the rods with technological defects. The critical size of the crack depending on the critical depth of corrosion-fatigue cracks ac in the rods and the corresponding areas of the fracture zones S sfz from the applied cyclic stresses σ is substantiated. It was established that the critical size of corrosion-fatigue cracks formed in production conditions under the action of low stresses of 60 MPa increased from 40 to 62% for changes in the diameter of the rod from 19 to 25 mm, respectively, and under the action of stresses twice as high (about 120 – 140 MPa) the range of change a c / d 0 decreased to 24 – 36%. Comparative experimental studies of steel and fiberglass sucker rods on fatigue endurance as close as possible to full-scale ones were conducted. According to the results of the experiments, we obtained dependence between the used resources of the rods (by the incubation period until cracks up to 2 mm deep were detected in them). In steel rods, the fatigue life exhaustion factor before the appearance of such cracks ranges from 0.18...0.4 with increasing load from 100 to 150 MPa. The rate of crack growth in both steel and composite rods at the stage of their pre-critical growth varies in the range of 10 -9 ...10 -8 m/cycle. References 1 Kopei, B. V., Zvirko, O. I., Venhrynyuk, T. P., Slobodyan, Z. V., Shtoiko, I. P. 2020. Elevation of the fatigue strength of sucker rods as a result of treatment with a special medium, Materials Science. 56 (1), 125 – 131. 2 Kopei. B. V., Stefanyshyn. A. B., Venhrynyuk. T. P. 2019. Fatigue strength of hybrid sucker rods. Materials Science. 54 (5), 739 – 742. 3 Kopei. B. V., Krechkovska. H. V., Nisonskyi. V. P. Bakun, B. M. 2021. Regularities of growth of fatigue cracks in hybrid suckering rods. Materials Science, 57 (4), 549 – 556. 4 Kopei, В.V, Kopei, V.B., Kopei, І.B. 2009. Sucker rods for sucker ing units. Моnograph. Ivano-Frankivsk, IFNTUOG, pp. 406 (in Ukrainian). Kret, N. V., Svirska, L. M., Venhrynyuk, T. P. 2020. Corrosion-fatigue crack propagation in exploited sucker rods made of 20N2M steel. Materials Science. 56 (2), 279 – 283. Sutherland, H. J. Mandell, J. F. 2004. The effect of mean stress on damage predictions for spectral loading of fiberglass composite coupons.specialty conference on making torque from the wind, EWEC, 93 – 108.