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    Measurement of Fracture Toughness by Instrumented Impact Test

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    Previous studies of the Charpy impact test using instrumented pendulum or anvil with V-noteh steel specimens are reviewed. It is concluded that such results add little to the usefulness of the test since even cleavage fractures are normally well beyond yield. No fracture toughness index emerges other than the simple measure of energy from the pendulum. In a second generation of work, fatigue cracked and side grooved (fcsg) specimens promoted below yield fractures up to about the 50 percent fracture appearance transition temperature (fatt). These results have been analysed by linear fracture mechanics to give the dynamic fracture toughness KID. In this interpretation understanding of the oscillations in load records due to specimen vibration is important. Results are discussed in the light of recent studies including an analog model with which near quantitative agreement is found. An improved simple correction factor for inertia loading effects is presented. It is concluded from both this work and supporting measurements of KID by other techniques that dynamic fracture toughness KID can be measured for low-strength steels using the instrumented fcsg impact test subject to the precautions and corrections discussed. Typical values of KID for mild steel are 60 ksi √in. at 0 C falling to 30 ksi √in. at -60 C. The significance of these low values in relation to the much higher static toughness is discussed briefly.


    impact tests, fracture toughness, steels, dynamic tests, notch tests, brittle fracture, strain rate, evaluation, tests

    Author Information:

    Turner, CE
    Reader in mechanical engineering, Imperial College, London,

    Committee/Subcommittee: E28.07

    DOI: 10.1520/STP32058S