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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The ultrasonic fatigue testing time was very short for this polymeric material: ranging from 12 secs for the low displacement specimens (12  m), to 4.5 secs for the high displacement specimens (18  m). In Figure 5 is plotted the neck section temperature evolution from the test start to fracture, for both last specimens.

Fig. 5. Maximum temperature registered at the neck section of specimen during ultrasonic fatigue testing of PMMA, for two displacements at the specimen ends: 12  m and 18  m. The tendency lines on Figure 5 were obtained by logarithmic regression, the corresponding equations are as follows: T = 15.913ln(t) + 13.966 for 12  m of displacement, and T = 21.145ln(t) + 34.167 for 18  m of displacement. The highest temperature registered during the ultrasonic fatigue tests with immersed specimens was close to 65° C, this represent 59% of the glass transition temperature for this polymeric material. Under the last temperature condition, it is assumed predominant mechanical effect over thermal effect, on the ultrasonic fatigue results of this material (Huang et al., 2014, Liu et al., 2008).

3. Results and discussion 3.1 Ultrasonic fatigue endurance of PMMA

Ultrasonic fatigue results have been obtained on the PMMA specimens, shown in Figure 2c, under zero mean stress rate R= -1 and immersed in a liquid simulating the human saliva. In Figure 6 are plotted the experimental points and the corresponding no-linear regression S-N curve.

5 6 7 8 9 10 50000 100000 150000 200000 250000 300000 Stress (MPa) Number of cycles Ulrasonic fatigue endurance of PMMA

Fig. 6. Experimental points and potencial tendency line for ultrasonic fatigue endurance of PMMA.