Abstract
In situ observation of crack growth was carried out during the creep crack growth test using a test specimen with two cracks. When crack propagation was confirmed by in situ observation, the creep load was reduced by 16% to prevent fracture due to plastic collapse. A marking line was drawn on the surface of the test piece as a method of confirming the propagation of the crack. The crack propagation could not be visually observed before the start of the creep test, but as soon as the loading started, the crack opened, and the tip of the crack could be visually observed. Immediately after the start of the creep test, it was possible to confirm that the plastic region expanded in the primary creep region, that cracks were slightly propagating in the secondary creep region, and that cracks opened and propagated rapidly in the tertiary creep region. In-situ observation of surface crack growth during the creep crack growth test revealed that the creep crack growth region could be extended by reducing the applied load before plastic collapse occurred.
