ASTM E2248-12

There are cases where it is impractical or impossible to prepare conventional CVN specimens. MCVN specimens are an alternative approach for characterizing notched specimen impact behavior. Typical applications include MCVN specimens prepared from the broken halves of previously tested specimens, from thin product form material, or from material cut from in-service components.

This standard establishes the requirements for performing impact tests on MCVN specimens fabricated from metallic materials. Minimum requirements are given for measurement and recording equipment such that similar sensitivity and comparable measurements, as compared to conventional CVN tests, are achieved. The user should be aware that the transition region temperature dependence data obtained from MCVN specimens are not directly comparable to those obtained from full-size standard Charpy-V specimens and suitable correlation procedures have to be employed to obtain ductile-to-brittle transition temperature (DBTT) data equivalent to those obtained using CVN specimens. In all instances, correlations will have to be developed to relate upper shelf energy (USE) data from MCVN test to CVN comparable energy levels. Application of MCVN test data to the evaluation of ferritic material behavior is the responsibility of the user of this test method. MCVN test data should not be used directly to determine the lowest allowable operating temperature for an in-service material. The data must be interpreted within the framework of a fracture mechanics assessment.

While this Test Method treats the use of an instrumented striker as an option, the use of instrumentation in the impact test is recommended and is fully described in Test Method E2298. In order to establish the force-displacement diagram, it is necessary to measure the impact force as a function of time during contact of the striker with the specimen. The area under the force-displacement curve is a measure of absorbed energy. As an alternative, absorbed energy may be evaluated directly from machine dial reading. Whenever possible, an optical encoder shall be used in place of the machine dial because an encoder has better resolution than a dial.

1.1 This test method describes notched-bar impact testing of metallic materials using Miniaturized Charpy V-Notch (MCVN) specimens and test apparatus. It provides: (a) a description of the apparatus, (b) requirements for inspection and calibration, (c) safety precautions, (d) sampling, (e) dimensions and preparation of specimens, (f) testing procedures, and (g) precision and bias.

1.2 This standard concerns Miniaturized Charpy V-Notch specimens, for which all linear dimensions, including length and notch depth, are reduced with respect to a type A standard impact test specimen in accordance with Test Methods E23. These are not the same as sub-size specimens, described in Annex A3 of Test Methods E23, for which length, notch angle and notch depth are the same as for the standard type A Charpy specimen. See also 1.5 below.

1.3 Comparison of the MCVN data with conventional Charpy V-Notch (CVN) data or application of the MCVN data, or both, to the evaluation of ferritic material behavior is the responsibility of the user of this test method and is not explicitly covered by this test method.

1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.5 This standard does not address testing of sub-size specimens as discussed in Test Methods E23. The reader should understand the distinction between miniature and subsize. Miniature specimens are shorter that sub-size specimens so that more tests can be conducted per unit volume of material. Moreover, miniature specimens are designed so that the stress fields which control fracture are similar to those of conventional Test Methods E23 specimens.

1.6 The MCVN test may be performed using a typical Test Methods E23 test machine with suitably modified anvils and striker or using a smaller capacity machine.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.