Three-dimensional constraint theory: Bridge the gap from laboratory material tests to fatigue fracture of engineering structures

The methods to assess structural strength and fracture theories have been developed for several decades, and have been successful for many specific engineering applications. Here we report the recent progresses from two-dimensional (2D) to three-dimensional (3D) fracture theories based on two-and three-parameter descriptions, such as K-T_z, J-T_z and K-T-T_z, J-Q_T-T_z, and their applications in bridging the gap from academic researches and material tests in laboratories to practical engineering structures. Here, T and Q are parameters for in-plane constraints, while T_z is the out-of-plane constraint factor as a ratio of the out-of-plane stress to the sum of in-plane stresses. The following critical issues will be addressed: 1) From 2D fracture mechanics to 3D fracture mechanics; 2) From tensile to mixed mode loadings; 3) From static/toughness to fatigue/durability; 4) From ambient to complex environments; 5) From empirical design to predictive design; 6) From design to fatigue life assessment.