SYMPOSIA PAPER Published: 01 January 1995

Three-Dimensional Crack Growth Assessment By Microtopographic Examination


The initial stage of the stable tearing process in two 2.3 mm sheet 2024-T3 aluminum alloy M(T) specimens are analyzed using fracture surface microtopography reconstruction techniques. The local crack tip opening angles (CTOA) in the interior of the specimens are determined relative to both crack extension and through-thickness position. The microtopographic analysis of cracks grown in the L-T and T-L orientations reveal that interior CTOA is comparable to those measured on the surface using standard optical analysis methods. Similar to surface CTOA results, interior (mid-thickness) CTOA exhibit a transient behavior; CTOA transitions from high angles, at near crack initiation, to a lower steady-state value of 5 deg. and 4.2 deg. for L-T and T-L, respectively, at crack lengths greater than 1.5 mm Fracture surface topographic projection maps are used to study the evolution of crack front tunneling during the initial stage of the fracture process. Stable tearing initiates at mid-thickness followed by a crack front tunneling process to a depth of approximately 2 mm. A brief discussion of the basis of the fracture process reconstruction method is provided and comments on the general utility of microtopographic fracture surface examination for general assessment of elastic-plastic and fully-plastic fracture processes are made.

Author Information

Lloyd, WR
Idaho National Engineering Laboratory, Idaho Falls, ID, USA
Piascik, RS
NASA - Langley Research Center, Hampton, VA, USA
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Developed by Committee: E08
Pages: 303–318
DOI: 10.1520/STP16391S
ISBN-EB: 978-0-8031-5311-0
ISBN-13: 978-0-8031-1996-3