PSI - Issue 3

G.M. Domínguez Almaraz et al. / Procedia Structural Integrity 3 (2017) 562–570 Author name / Structural Integrity Procedia 00 (2017) 000–000

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removed from testing specimen to fix the bolt and the total masse of testing specimen increases with the steel screw bolt, decreasing the natural frequency of vibration to a value closer to 20 KHz. The relationship between the displacements at the ends of testing specimen and the induced maximum stress at the neck section was obtained by numerical simulation, as shown in Figure 3a and 3b. The maximum Von Mises stress induced at the neck section with the tension displacement of 12  m was 5.96 MPa, Figure 3a; whereas this value increases to 8.94 MPa, when the displacement rises to 18  m, Figure 3b. A linear relationship is obtained between the displacement at the extremes of specimen and the maximum Von Mises stress induced at the neck section: 1  m of displacement at the ends induces 0,5 MPa approximately of tensile stress at the neck section.

(a) (b) Fig. 3. (a) Von Mises stress distribution along the specimen with 12  m of displacement, and (b) Von Mises stress distribution along the specimen with 18  m of displacement. 2.3 Thermographic analysis during ultrasonic fatigue testing Thermographic images were taken during the ultrasonic fatigue testing to investigate the temperature behavior of immersed specimens. Ultrasonic fatigue tests without immersion in the liquid simulating the human saliva were not possible, since temperature at the neck section has attained 139° C and the resonance condition was interrupted, Figure 4a. In Figures 4b and 4c are shown the maximum temperatures attained during ultrasonic testing of immersed specimens with 12 and 18  m of displacement at the ends, respectively.

(a) (c) Fig. 4. (a) Temperatures obtained by thermographic technique of specimen without immersion, (b) Thermographic temperatures of specimen with immersion and 12  m of displacement, c) Thermographic temperatures of specimen with immersion and 18  m of displacement. (b)