Proposing a New Crack Driving Force Parameter for Fatigue Crack Growth Rate of C–Mn Steel

The present study is aimed at analyzing the fatigue crack growth rate data on compact tension (CT) and three-point-bend (TPB) specimens of C–Mn steel under different positive load ratios. Detailed elastic–plastic finite element analyses have been performed using nonlinear kinematic hardening rule of Chaboche material model. The numerically calculated plastic zone ahead of crack tip has been compared with measured plastic zone using digital image correlation technique. The fatigue crack growth rate curves have been analyzed with respect to different crack driving forces such as (i) single-parameter stress intensity factor (SIF) range, (ii) two-parameter-based SIF ( $K^{*}$), and (iii) cyclic plasticity zone–based models. A new crack driving force has been proposed considering cyclic plastic zone and representative plastic strain accumulation within this zone. The $K^{*}$ parameter and proposed model resulted in improved assessments for different load ratios and constraint geometries (CT and TPB).