The fatigue life estimation method from the stress concentration region with zero defect - An application to the fatigue crack growth simulation code "FLARP" for the in-plane gusset welded joint

In-plane gusset welded joints are very popular and used in many steel constructed structures. Fatigue life estimations for this type of joint have been performed by applying the fatigue crack growth simulation code "FLARP" developed by the authors. The fatigue crack shows the typical opening / closing behavior during fatigue crack growth. The plastic deformed layer in the crack wake, which represents the loading history indirectly, contributes to the behavior. The consideration of crack closure is essential in the estimation of the fatigue life. FLARP enables the quantitative simulation of the fatigue crack opening / closing. By considering the cyclic plastic behavior ahead of a fatigue crack tip, the improved effective stress intensity factor range (ΔK_RPG) to denote the fatigue crack propagation law, which is formulated by replacing the crack opening load with the Retensile Plastic zone Generating load (RPG load), was defined. ΔK_RPG is adopted as the parameter for the fatigue life estimation by FLARP. The validity of the fatigue life estimation by FLARP is confirmed by comparing the estimated S-N curves with the experi mental results for the in-plane gusset welded joints.