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Review and Consideration of Apparent Negative Crack Growth in Fracture Toughness Tests



Enrico Lucon


Apparent negative crack growth is often encountered when performing elastic-plastic fracture toughness tests with the Elastic Compliance single-specimen technique. It consists of a decrease of specimen compliance (reduction of crack size) during the early portion of the test, before the attainment of maximum force and the onset of ductile crack extension. This phenomenon was recognized and discussed inside the fracture mechanics community since the mid-1980s, but widespread consensus was never achieved on its root causes and on the best approach to account for it in the analysis of an elastic-plastic fracture toughness test. It has been shown that both experimental (test setup) and material behavior aspects can be invoked to explain the decrease of elastic compliance that translates into decreasing crack size in the early loading stage. The current edition of ASTM E1820 does not offer provisions to handle this phenomenon, and users are left free to treat the issue as they see fit. In this study, several papers published in the last 40 years were reviewed, and different proposed methods were applied on 15 selected J-R curve tests performed on specimens of different geometries and thicknesses. Comparisons between original crack sizes, ductile crack extensions, and critical toughness values are presented, and recommendations are provided for revising E1820 with due consideration of the occurrence of apparent negative crack growth.
Materials Performance and Characterization


Apparent negative crack growth, ASTM E1820, crack tip blunting, elastic compliance tests, elastic-plastic fracture toughness, J-R curve


Lucon, E. (2024), Review and Consideration of Apparent Negative Crack Growth in Fracture Toughness Tests, Materials Performance and Characterization, [online],, (Accessed April 19, 2024)
Created February 15, 2024, Updated March 2, 2024