Inverse of Wallin's relation for the effect of strain rate on the ASTM E-1921 reference temperature and its application to reference temperature estimation from Charpy tests

Abstract

An inverse relation to that of Wallin's strain rate equation has been obtained for predicting the static reference temperature from dynamic results. Wallin strain rate equation (WSRE) predicts the reference temperature at faster loading rates (expressed as stress intensity factor – SIF-rates) from room temperature yield strength (RT-YS) and quasi-static reference temperature, T 0. The inverse WSRE (IWSRE) predicts T 0 from T 0 dy , that is, T 0 at dynamic loading rates as obtained in impact and other dynamic tests. For this purpose, the same dataset that was used by Wallin for deriving the original WSRE has been used. It has also been found that the dynamic reference temperature obtained by applying the modified Schindler procedure (MSP) to Charpy V-notch (CVN) impact tests, that is, T QSch dy , provides a conservative or close estimate of reference temperature corresponding to a loading rate of ∼10 6 MPa √m s −1. Then using the T QSch dy in the IWSRE along with RT-YS and SIF rate of 10 6 MPa √m s −1, results in an estimate of quasi-static T 0, namely, T QMSP-IW, the subscript indicating use of both the MSP and IWSRE. An equation directly correlating T QSch dy to T 0 has also been obtained. The estimates of T 0 from this direct correlation are referred as T QMSP, the subscript indicating the use of MSP. It has been shown that the larger of the two estimates, T QMSP-IW and T QMSP, provides a reasonably accurate, but conservative estimate of T 0 and is termed – T QSchW, to indicate the use of both the MSP and IWSRE procedures. T QSchW is a promising estimate for steels with T QSch dy less than 60 °C – termed T Q-est, to indicate the estimated reference temperature value; for steels with T QSch dy > 60 ° C , T Q-est is the larger of the two estimates, namely, T QM2 and T QSchW. The equation reported in the literature correlating the brittleness transition temperature, T D (obtained from instrumented Charpy V-notch – CVN – impact tests), though has a tendency to accuracy and ease of estimation, is not suitable for making conservative reference temperature estimates, because of excessive scatter and lack of robustness in T D estimation. The shifts in T Q-est, namely, Δ T Q-est, are acceptably conservative even for the highly irradiated steel. For the high reference temperature steels and low upper shelf inhomogeneous steels, the anomaly of T Q-est being larger than RT NDT indicates that the conservatism of even the RT NDT approach is not much for such steels. A very useful application of the procedures in this paper is that the T Q-est or ( T Q-est – 20 °C) can provide a convenient test temperature for performing the tests as per ASTM E-1921 test standard for determining T 0. The whole procedure or methodology detailed in this paper for obtaining the conservatively estimated reference temperature, T Q-est, is designated as IGCAR-procedure, IGCAR being the acronym for the author's organization.