Estimation of the Reference Temperature, T0, by Means of the Small Punch Testing Technique

Abstract

The extension of the operation period of nuclear plants requires an accurate characterisation of the vessel materials, in order to monitor their embrittlement due to neutron irradiation. This need poses a challenge, since the availability of specimens inside the vessels to characterise their evolution is rather scarce. Therefore, innovative techniques have to be applied, in order to reduce the number of tests and the volume of the specimens. In this paper, the Master Curve approach has been employed, combined with the use of small punch notched specimens. The Master Curve methodology allows to evaluate the embrittlement of the material using a single parameter: the reference temperature, T0. This parameter has been estimated for several steels by means of modified small punch specimens, which are characterised by their reduced dimensions: only 10 × 10 × 0.5 mm. The obtained results have been compared with those obtained by means of conventional testing and a methodology to estimate T0 by means of small punch tests together with the Master Curve has been proposed.

Influence of the notch length on the estimation of the reference temperature by means of the small punch test

“…Further research should be performed in order to achieve a better understanding of its influence. The obtained reference temperatures for the different notch lengths have been compared with previous research [13,14], where S275JR and S460M steels had been tested with a notch length of approximately 4.4 mm and a correlation factor between T0 SP and T0 of 0.52 had been established. It can be seen that the relationship provides accurate results for all the materials tested at the same notch length, of approximately 4.4-4.5 mm.…”

“…According to previous works [13,14], to guarantee the applicability of the MC approach, the onset of cleavage cracking is the criterion of validity. After performing analysis of the micromechanisms present at the crack initiation, it has been proven that those tests exhibiting a sudden drop of the force at maximum force or those tests with a discontinuity on its slope on the proximity of maximum force exhibit pure cleavage or mixed fracture mechanisms respectively, being both valid for the determination of T0 SP [13,14].…”

“…Several approaches have been proposed, such as the use of the equivalent fracture strain [9] or finite element modelling [10], among which the use of lateral notches results highly remarkable [11,12]. This geometry has been recently applied to the estimation of the reference temperature on several ferritic and pressure vessel steels with promising results [13,14]. In these previous works, a fixed notch length has been employed, which might have had some influence on the results obtained.…”