ミニチュア試験片によるクリープ破断特性の評価
1992 年 41 巻 460 号 p. 112-118
詳細
1992 年 41 巻 460 号 p. 112-118
Evaluation of service reliability of components, particularly the remaining service lifetime of materials, has become a very important matter for thermal power stations and other plants. The remaining lifetime is usually assessed with a fair precision from aggravation of mechanical properties, especially that of creep characteristics. One difficulty here is that, if the precision of prediction is to be improved over what is available with today's in-situ nondestructive methods, one needs to take samples directly from operating machines, whereby one has to be satisfied with a small quantity of samples. This calls for establishment of a trustworthy method for evaluating creep rupture characteristics with a small number of small-size specimens.
The following observations and conclusions were made in the present study.
(1) The miniature specimen creep tester, developed here with a testing chamber maintained airtight with a pair of O-rings, performed quite well, in which the combined effect of internal Ar pressure and O-rings could be safely ignored.
(2) In Ar atmosphere to forestall oxidation, the rupture time obtained with the 2mm diameter miniature test specimens agreed quite well with that obtained with the 8mm diameter conventional test specimens.
(3) The effect of oxidation to degrade the rupture time became manifest above 600°C.
(4) The major cause of this degradation is an increase in true stress arising from the loss of material due to oxidation.
