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

摘要

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_o. 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 Vms~(-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℃ - termed T_(Q-est) to indicate the estimated reference temperature value; for steels with T_(QSch) ~(dy) > 60 ℃, 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, ΔT_(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 RTndt 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 ℃) 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.