Estimation Scheme of Residual Lives for elevated Temperature Components Using Total Information of Nano and Macro Sizes

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A new testing apparatus where constant load is directly applied to a very small disc-type specimen is developed to evaluate creep lives of components at elevated temperatures : Small Punch Creep (SPC) testing apparatus. Since failure of structural components mainly breaks out around maximum damaged portion, and heavily damaged components dominate the residual life of structural systems, a methodology to assess the local damage and residual life in components under creep temperature have been required. However, conventional uni-axial creep specimens need a certain amount of volume, and this often causes a difficulty to repair specific devices after sampling uni-axial creep specimens. Dimensions of the disc-type specimen here employed are very small : 10 mm in diameter and 0.5 mm in thickness. After designing and installing the new SPC testing apparatus, as series of SPC tests are conducted using super duralumin. It is clarified that the primary and the secondary creep regimes occupy most of the creep deformation, and that the tertiary creep appears just before fracture. Furthermore it is shown that creep rupture lives obtained in the SPC test have a good correlation with those from uni-axial creep tests.Since the initial SPC apparatus has not had a specific vessel to prevent oxidation for ferritic steels over the creep temperature regimes, in the second fiscal year a new SPC testing apparatus was developed where a thin walled pipe and a small vessel were attached to perform little oxidation atmosphere. Unfortunately oxide scale about 20μm in thickness was formed on the surface of disc specimens due to either a lack of the flow of Argon gas or inadequate. However a relation between the load in the SPC test and the stress in the creep test is described as a power low function.