Issue 42

A. Strafella et alii, Frattura ed Integrità Strutturale, 42 (2017) 352-365; DOI: 10.3221/IGF-ESIS.42.36 359 To date, the test at 500MPa is still in progress: the strain is 0.46% and the test duration is 885h. The comparison among all lead curves up to 600h is depicted in Fig. 10, where primary and secondary phases of creep are shown: it can be clearly recognized them and the calculation of sscr was possible. Figure 8 : Characteristic creep curve sscr-stress. Figure 9 : Creep curve in lead. To highlight the lead effect, creep curve obtained from the test on specimen in air was compared with that obtained in lead. The comparison between creep curve in air and in lead at 560MPa is depicted in Fig. 11. As expected, an increase in creep strain was observed, but it isn’t really relevant, until the value of 800h: creep curves in lead and in air showed the same shape with a difference of creep strain percentage around 0.04% and it concerned only the primary creep; moreover, the strain rate is the same. 250 300 350 400 450 500 550 600 1E-5 1E-4 1E-3 n= 4.13 A= 5.90*10 -16 sscr-curve sscr-experimental points air sscr [%/h stress 0 200 400 600 800 1000 1200 0,0 0,2 0,4 0,6 0,8 1,0 1,2 creep strain % Creep Strain % - [575MPa]- Pb Time [h] T= 550°C in Pb