Predicting reference temperature from instrumented Charpy V-notch impact tests using modified Schindler procedure for computing dynamic fracture toughness

摘要

Reactor pressure vessel (RPV) steels are increasingly being characterised in terms of the reference temperature T_0 and the associated Master Curve (MC) Procedure, following the ASTM E-1921 standard. Though correlations have been proposed to predict the T_0 from Charpy transition temperature T_(28J) or instrumented impact test parameters like T_(4kN), none can be taken as a universal correlation. Here we are proposing a new correlation of T_0 with T_(0Sch)~(dy), where T_(0Sch)~(dy) is the reference temperature corresponding to a median K_(Id)=100 MPa√m evaluated by the ASTM E1921 procedure applied to K_(Id) vs T data, and K_(Id) has been calculated from instrumented CVN impact test data using modified Schindler relations. This will provide a reliable method for determining T_0 from instrumented CVN tests alone. T_(0Sch)~(dy) provides a conservative alternative to T_0~(dy) for application of the ASTM E 1921 MC procedure in dynamic situations. Since the above procedure depends only on instrumented CVN data, it will be less costly to apply (no precracking is necessary) and will also obviate the difficulties associated with determining T_0~(dy) from precracked CVN testing (because of severe size limitations, associated scatter and signal oscillations from the mechanics of the test, there needs to be precise control over test temperatures and test velocity for obtaining valid data from limited number of specimens). The RT_(NDT)(est) from the suggested procedure (or its modifications based on future work) will provide an acceptable alternative to RT_(NDT) for application of the ASME K_(IR) curve based on instrumented CVN tests alone. For low-uppershelf steels, the new reference temperature estimate T_(0.075) and its correlation to T_(0Sch)~(dy) will provide a methodology for application of MCs to such steels. Further comprehensive work is needed to validate the procedures and correlations suggested in this paper.