Estimation of plastic zone at crack tip under fatigue loading of AA6061-T6 aluminum alloy by finite element analysis using ANSYS

Abstract

The plastic zone shape and size are analytically estimated at crack tip under fatigue loading (at stress ratio (R) = 0.1 and 0.5) of AA6061-T6 aluminum alloy by finite element analysis using ANSYS. The stress intensity factor (SIF) is a measure of the mechanical force required for crack growth and is closely related to the plastic zone formed in the vicinity of the crack tip. The stress intensity factor range (ΔK) was determined by finite element analysis using ANSYS and was compared with the experimental data obtained as per ASTM standard to decide the applicability of the analytical method in the present work. The comparison exhibited that the error to determine SIF using ANSYS is less than 20%, which lie under acceptable range. The finite element analysis was applied to determine the plastic zone shape and size at crack tip using ANSYS. A butterfly type of cyclic plastic zone was observed in the plane strain condition. At lower ∆K, smaller plastic zone was measured for R = 0.5 in comparison to R = 0.1. After ∆K = 12.00 MPa√mm, comparatively larger area of plastic zone was observed for R = 0.5. At constant ΔK = 12.88 MPa√mm, the value of maximum SIF (Kmax) was obtained as 14.29 MPa√mm and 16.11 MPa√mm at stress ration (R) = 0.1 and 0.5, respectively. It was also observed that at same Kmax = 16.55 MPa√mm, the value of ΔK is 14.86 and 18.13 for R = 0.1 and 0.5, respectively. The increased value of ΔK results in larger plastic zone for R = 0.5 at later stage of crack growth.