Research on Correlation between Charpy Impact Test and Fracture of Steel Members

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Since the Charpy impact test was invented a hundred years ago, the test method has been utilized in steel industry all over the world. The test results, however, have never been related quantitatively to fracture performance of structural members of actual size. Fracture mechanics has shown a negative opinion to the correlation between Charpy and structures because of the substantial differences in size, loading rate and notch configuration.This research, however, prevailed that there is a remarkable correlation of pattern and process of fracture between Charpy specimens and structural members. They have a common fracture mechanism, i.e., a sequence of ductile crack initiation, its growth, and transition to cleavage fracture. Furthermore, the load-deformation curves obtained from Charpy test under variable loading rates, when compiled together with FEM analysis, demonstrated the development of plastic stress and strain at the origin of fracture, from which the conditions of crack initiation and brittle transition can be expressed by a common formula both for Charpy specimens and structural members with necessary conversions. Thus, the energy absorption capacity gained from Charpy impact test is expected to be directly applied for estimating the plastic strength and deformation capacity of structural members in design of steel structures.