Issue 42

A. Strafella et alii, Frattura ed Integrità Strutturale, 42 (2017) 352-365; DOI: 10.3221/IGF-ESIS.42.36 355 Figure 2 : overall sketch of testing cell with both the longitudinal and cross sections. Figure 3: Cell assembly, designed and manufactured for tests in lead, on a MAYES machine during the specimen fixing and with its furnace. R ESULTS AND DISCUSSION Creep curves in air he specimens were tested at 550°C under constant loads, corresponding to the initial tensile stresses in the range of 300-560 MPa, and the experimental data allowed to obtain the typical creep curves of 15-15Ti(Si). The most relevant curves were depicted in Fig. 4, where the evolution of the creep strain with time at various stress levels is plotted. If we consider the same time value in the graph, it can be observed that the creep strain increased with the applied stress; moreover it can also noticed that at 560MPa, the rupture was reached at 1165h, while the tests at 300, 400 and 500MPa are still in progress. The shape of creep curve is consistent with the expectations: after long time (more than 1000h), at 300 and 400 MPa, the strain curves didn’t reach the tertiary creep stage, still remaining in the secondary creep phase; at 500 MPa, although is still ongoing, the creep curve clearly shows a defined primary and secondary stages. At stress values near the yield strength of T Specim Lead container