The elastic and plastic constraint parameters for three-dimensional problems

•Fracture toughness was studied through experiments and computations.•Distinctions in the behavior of constraint parameters for SENB and CS were observed.•The plastic SIF is sensitive to the in-plane and out-of-plane constraint effects.•The plastic SIF is attractive as unified fracture resistance characteristic. Fracture toughness and the in-plane and out-of-plane constraint effects are studied through experiments and computations for high-strength carbon steel 34ХН3МА. The subjects for the studies are single-edge-notched bend specimens under three-point bending and compact specimens under tension. Both types of specimens are of non-standard configuration because the specimen thickness-to-width ratio was varied in the range of 0.1–1.0, and the relative crack length was changed in the range of 0.24–0.64. Characterization of the constraint effects was performed using the non-singular T-stresses, the local triaxiality parameter h, and the TZ and TZZ, factors of the stress-state in a 3D cracked body. For the particular geometries of the specimens considered, the numerical constant of the plastic stress field In and the plastic stress intensity factor distributions along the crack front are obtained as a function of the dimensionless crack length and the specimen thickness. It is further demonstrated that the plastic stress intensity factor accounting for the in-plane and out-of-plane constraint effects can be used to characterize the fracture resistance characteristics as a unified single parameter for a variety of specimen geometries.