Mode I elastic-plastic fracture theory from the perspective of fracture process zone

The problem of elastoplastic crack propagation in isothermal or room temperature environments, typified by the failure of thin-walled aircraft metallic structures, poses a severe challenge to the applicability of Linear Elastic Fracture Mechanics (LEFM) and J-integral theory due to characteristics such as large-scale yielding and stable crack growth. Despite the successive proposal of various parameters—including fracture strain, Crack Tip Opening Angle/Displacement (CTOA/D), Essential Work of Fracture (EWF), and incremental crack-tip integrals—the distinct physical interpretations, ambiguous interrelationships, and questionable “transferability” of these parameters have severely hindered the development of a unified theory and its engineering applications. To address this dilemma, this paper constructs a unified theoretical framework for elastoplastic fracture, adopting the Fracture Process Zone (FPZ) as the core perspective under the simplifying assumptions of neglecting thermal source effects and body forces. This framework not only offers a unified and self-consistent explanation for historical conundrums such as the Rice paradox but also systematically demonstrates that mainstream parameters, including incremental integrals, CTOA/D, fracture strain, and EWF, are intrinsically equivalent to the driving force on “steady FPZ”, thereby revealing the inherent unity among existing elastoplastic fracture parameters. Furthermore, by elucidating the thermodynamic significance of the power balance laws for a body with an extending crack, the framework establishes the FPZ as an independent thermodynamic system possessing “autonomy”, providing a solid theoretical foundation for the “transferability” of fracture parameters. This paper aims to systematically elaborate on the construction process, core arguments, and academic significance of this theoretical framework.