PSI - Issue 54

Ana Dantas et al. / Procedia Structural Integrity 54 (2024) 593–600 AnaDantas / Structural Integrity Procedia 00 (2023) 000–000

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In order to determine the current to apply to the system in each accelerated corrosion procedure and the duration, the same equation was manipulated as to isolate these parameters (see Eq 3). Lastly, the condition ∆ m 2 = ∆ m 1 was imposed:

∆ m 2 nF ( AM )

(3)

It =

As a result, it was defined that each specimen would be pre-corroded through the application of a current, higher than I corr , 0.25 A for a period of 8745 s ( ≈ 2h26min). This imposed surface corrosion would translate into a theoretical mass loss of 0.633 g, which is equivalent to half an year of not artificially induced corrosion. The material degradation took the form of uniform corrosion and pitting distributed over the entire exposed surface. There was, however, some level of variation in the number of pits and pit sizes within the range of specimens. Based on the registered mass before and after corrosion, the average mass loss for the tensile and the fatigue specimens was calculated. An average value of 0.674 g was obtained, which represents a variation of 6% in relation to the theoretical value (0.633 g). The standard deviation and coe ffi cient of variance were calculated and are respectively 0.04 and 6.41 %. These low values point to a low dispersion, i.e., a consistency in mass loss throughout all specimen With the purpose of determining some of the main mechanical properties of the steel corresponding to a state of surface corrosion, quasi-static tensile tests were conducted according to the standard ASTM-E8 / E8M-22: ”Standard Test Methods for Tension Testing of Metallic Materials” (ASTM International, 2022). Five round-type specimens of the geometry presented in Figure 4 (a) were tested using the setup of Figure 4 (d). In Figure 4 is depicted a tensile specimen prior to corrosion (Figure 4(b)) and the five specimens already corroded (Figure 4(d)), illustrating the induced surface corrosion condition. The tests were performed with displacement control and at the velocity of 1 mm / min. 3. Quasi-static Tensile Tests

Fig. 4: Quasi-static tensile specimens:(a) 2D drawing (dimensions in mm); (b)initial state and (c) with half an year surface corrosion; and test setup

4. Results and Discussion

Bellow, in Figure 5 (a) are present the engineering stress and strain curves plotted using the values recorded during the tensile tests of the five pre-corroded specimens. Each specimen was labelled by the letter CR (referencing their surface state and geometry) followed by the specimen ID number. The specimens demonstrated some ductility, as necking was present during the tensile tests and visible in Figures 6 (a) and (b). Additionally, large elongations at ultimate strength and after fracture were registered, averaging 6.63 % and 19.39% respectively. Furthermore, the young’s modulus was around 200 MPa, the yield strength was above 690 MPa and the ultimate strength was around 805 MPa (all values are listed in Table 1). The standard deviation and coe ffi cient of variance were calculated for each mechanical property and point to a low dispersion of the experimental data.