SEDL / STP / STP1461-EB / STP11514S

Characterization of Crack Length Measurement Methods for Flat Fracture with Tunneling

James, MA
Staff Scientist, National Institute of Aerospace, Hampton, VA

Newman, JC
Professor, Mississippi State University, Mississippi State

Pages: 26    Published: Jan 2005

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Abstract

This paper compares area-average and unloading compliance crack-growth values with experimental crack-front shapes recorded at various stages of crack growth during fracture tests conducted on 2024-T351 aluminum alloy plate. Crack-front shapes were determined by fracturing the specimen up to a predetermined amount of crack growth and fatigue cycling the specimen for about 4000 cycles at a high stress ratio to mark the crack-front location. For each shape, the area-average and unloading compliance crack lengths were determined. Boundary collocation results provide an approximation to the δ⁵ unloading compliance crack length. The crack tunneling results show that the area-average technique produces crack-length measurements more representative of the straight-front finite element analyses than optical based surface measurements. The δ⁵ technique is significantly more sensitive to tunneling than the CMOD technique and is easier to apply than the area-average technique.