Novel framework for predicting constraint effects on fracture toughness using an elastic–plastic phase field model and modified boundary layer formulations

•Constraint effects on fracture toughness are predicted using an elastic–plastic phase field model and modified boundary layer formulations.•The influence of plastic material properties on the constraint effects in fracture toughness is investigated.•The cleavage toughness under different T-stress is predicted using our approach.•The novel framework successfully captures the constraint effects in fracture toughness.