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

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, T0. The inverse WSRE (IWSRE) predicts T0 from T0dy, that is, T0 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, TQSchdy, provides a conservative or close estimate of reference temperature corresponding to a loading rate of ∼106 MPa √m s−1. Then using the TQSchdy in the IWSRE along with RT-YS and SIF rate of 106 MPa √m s−1, results in an estimate of quasi-static T0, namely, TQMSP-IW, the subscript indicating use of both the MSP and IWSRE. An equation directly correlating TQSchdy to T0 has also been obtained. The estimates of T0 from this direct correlation are referred as TQMSP, the subscript indicating the use of MSP. It has been shown that the larger of the two estimates, TQMSP-IW and TQMSP, provides a reasonably accurate, but conservative estimate of T0 and is termed – TQSchW, to indicate the use of both the MSP and IWSRE procedures. TQSchW is a promising estimate for steels with TQSchdy less than 60 °C – termed TQ-est, to indicate the estimated reference temperature value; for steels with TQSchdy>60 °C, TQ-est is the larger of the two estimates, namely, TQM2 and TQSchW. The equation reported in the literature correlating the brittleness transition temperature, TD (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 TD estimation. The shifts in TQ-est, namely, ΔTQ-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 TQ-est being larger than RTNDT indicates that the conservatism of even the RTNDT approach is not much for such steels. A very useful application of the procedures in this paper is that the TQ-est or (TQ-est – 20 °C) can provide a convenient test temperature for performing the tests as per ASTM E-1921 test standard for determining T0. The whole procedure or methodology detailed in this paper for obtaining the conservatively estimated reference temperature, TQ-est, is designated as IGCAR-procedure, IGCAR being the acronym for the author's organization.

Research highlights▶ An inverse relation for the Wallin strain rate equation (WSRE), that is, IWSRE, has been derived for predicting the static reference temperature from dynamic results. ▶ Using the IWSRE and some other correlations, a procedure, called IGCAR-procedure, has been developed for conservative estimation of the ASTM E-1921 reference temperature, T0-est, from Charpy V-notch ductile-brittle transition tests alone. The T0-est by the IGCAR-procedure is termed Tq-IGC to distinguish it from other estimates. ▶ Tq-IGC is neither too conservative nor unacceptably non-conservative. ▶ The Tq-IGC along with the conservative Master Curve procedure helps provide assuredly conservative lower-bound fracture toughness curve.