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Fatigue lives obtained from complex testing and monitoring of differentcomponents often involve some degree of discrepancy in results due to geometricalvariation, even when they are tested under controlled conditions, and have similarsurface cyclic strain range at the critical location. Recently, several fatigue modelswere developed to improve correlation of specimen lives using a critical 'process zone'that surrounds the damaged material. A review of such an approach is presented. Theapproach is based on critical subsurface strains and consists of fatigue damagesummation procedure in the affected area. The fatigue life prediction model is appliedto two structural materials using three geometries subjected to biaxial cyclic stresses.These include notched bar, rhombic plate and car component. The subsurface strainsare evaluated by using a detailed elastic-plastic finite element analyses and byconsidering critical subsurface fatigue paths. It is shown that in the several casesinvestigated the subsurface approach appears to have overcome surface lifeconservative predictions.