An elastic-plastic finite element analysis by using ANSYS is performed to simulate closure behaviour of fatigue cracks in center cracked tension(CCT) and single edged notch(SEN) specimens. Employment of constant element size hardly explains the experimental closure behaviour for the whole range of crack growth. Therefore, attention is given to the optimum element size, Δa according to crack length in relation to the plastic zone size, $ω_p$ of fatigue crack tip. A general crack length moving method in unwelded specimen is improper way to get $ω_p$/Δa because it is affected simultaneously by stress intensity factor and stress ratio. Another new method, crack length fixed method can predict successfully the effect of ratio because $ω_p$/Δa can be expressed only the function of stress ratio. Therefore, this method is proposed to determine the mesh configuration relevant to precise simulation of the observed crack closure behaviour. Moreover, finite element analysis by using optimum element size can predict successfully the parts of partial crack opening behaviour through transition region from residual compression to residual tension of SEN specimen as well as the normal fatigue crack opening behaviour through residual stress fields of CCT and SEN specimens. Specially, Δa-a relation can predict qualitatively the specification of experimental Δa/dN-a relation, because element size is crack growth rate per one cycle.
